[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 Jidong Xiao changed: What|Removed |Added CC||jidong.x...@gmail.com --- Comment #1 from Jidong Xiao --- Hi, I think this has been fixed since kernel 3.11, can you try any newer version, from 3.11 to 3.14, and see if you can still reproduce the problem? If not, then we can close this ticket. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #2 from Jatin Kumar --- Hello Jidong, thanks for the info. I will try and let you know. While you are at this, can you please help me another single stepping issue and the issue is: 1. While single stepping, the instruction immediately next to `out` (EE) instruction is skipped. I am not getting debug trap after the execution of `out` instruction completes. 2. Also is there anything special about `out` instruction that causes interrupts to come at instruction immediately next to it, when not running in single stepping mode. That would be a really great help in my project. Thanks in advance. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 Paolo Bonzini changed: What|Removed |Added CC||bonz...@gnu.org --- Comment #3 from Paolo Bonzini --- > 2. Also is there anything special about `out` instruction that causes > interrupts to come at instruction immediately next to it, when not running in > single stepping mode. The "out" instruction exits to QEMU and has a much higher latency than an bare-metal. This, plus the usage of mutexes in QEMU, may make it more likely that interrupts occur right after an "out" instruction. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #4 from Jidong Xiao --- Jatin, are you using gdb to do the single step?(In reply to Jatin Kumar from comment #2) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #5 from Jatin Kumar --- @Paolo: Thanks for the info. That makes sense to me. (In reply to Jidong Xiao from comment #4) > Jatin, are you using gdb to do the single step?(In reply to Jatin Kumar from > comment #2) No. I have been doing single stepping from inside the OS. It single steps its own code using debug trap untill some condition is met. During this whenever I hit an out instruction, the very next instruction is not skipped while single stepping. It may have been executing it because overall the code seems to be working correctly. I couldn't find anything online in this regard so I am curious if this is something QEMU specific. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #6 from Jatin Kumar --- (In reply to Jatin Kumar from comment #5) > whenever I hit an out instruction, the very next instruction is not skipped Sorry I meant 'is skipped'. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #7 from Paolo Bonzini --- Hi Jidong, no this is not fixed yet. Basically OUT instructions are emulated by KVM, and support for single-stepping and breakpoints in the emulator is quite minimal. 3.12 added some support but OUTs and writes to memory are still broken: commit 0912c9771e9902f752e890e93af495cc06a786ac Author: Paolo Bonzini Date: Tue Aug 27 15:41:43 2013 +0200 KVM: x86: add comments where MMIO does not return to the emulator Support for single-step in the emulator (new in 3.12) does not work for MMIO or PIO writes, because they are completed without returning to the emulator. This is not worse than what we had in 3.11; still, add comments so that the issue is not forgotten. Signed-off-by: Paolo Bonzini Signed-off-by: Gleb Natapov -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #8 from Jidong Xiao --- Hi, Jatin, "from inside the OS" means from within the Guest OS right? (In reply to Jatin Kumar from comment #5) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #9 from Jidong Xiao --- Hi, Paolo, It seems that Gleb's patch commit 03617c188f41eeeb4223c919ee7e66e5a114f2c6 "KVM: VMX: mark unusable segment as nonpresent" fixed a similar problem like this, look at this: https://bugzilla.redhat.com/show_bug.cgi?id=854983, Even though they are triggered by different reasons, they both cause the "hardware error 0x8021" issue. So I feel that patch could also fix this single step issue. (In reply to Paolo Bonzini from comment #7) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #10 from Paolo Bonzini --- No, hardware error 0x8021 includes pretty much everything that could go wrong in vmx.c. :) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #11 from Jidong Xiao --- Hi, Paolo, thanks for your explanation. I am interested in fixing this. So what's the technical challenge here? When you say "support for single-stepping and breakpoints in the emulator is quite minimal", do you mean it's a problem in the Qemu side, rather than something wrong in the kvm kernel modules? If so, and if we want to fix this, we need to make some changes in the Qemu code, right? (In reply to Paolo Bonzini from comment #10) > No, hardware error 0x8021 includes pretty much everything that could go > wrong in vmx.c. :) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #12 from Paolo Bonzini --- > Hi, Paolo, thanks for your explanation. I am interested in fixing this. So > what's the technical challenge here? The first step is to reproduce the failure. To do this you can make a patch to kvm-unit-tests (git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git). 0x8021 means invalid guest state in the VMCS (the VM information that is passed to the processor). So you could try adding some printk to understand what is the invalid guest state. To do this you need to download the Intel manuals (known as "Intel SDM", google is your friend). You can post the testcase patch on kvm@vger.kernel.org once you have a reproducer. > When you say "support for single-stepping and breakpoints in the emulator is > quite minimal", do you mean it's a problem in the Qemu side, rather than > something wrong in the kvm kernel modules? If so, and if we want to fix this, > we need to make some changes in the Qemu code, right? No, the emulator is part of KVM, see arch/x86/kvm/emulate.c. I have some pending patches for it, destined to 3.17. There is a small chance that they fix the bug. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #13 from Jidong Xiao --- Great, I will try. Yes I have the inter manual and I have studied it for a while, so basically I know the data structure of VMCS. To reproduce the failure, so, if I use gdb in a guest OS, like to debug a program inside the Guest OS, and run the single step command in gdb, that should trigger this bug right? Assuming the program includes a sti instruction. (In reply to Paolo Bonzini from comment #12) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #14 from Jatin Kumar --- (In reply to Jidong Xiao from comment #8) > Hi, Jatin, > > "from inside the OS" means from within the Guest OS right? > (In reply to Jatin Kumar from comment #5) Hello Jidong, Yes it means from within guest OS. Sample code block is like this: intr_register_int(1, 3, INTR_OFF, intr_debug_handler_out, "#DB Debug Exception"); asm volatile( "pushfl \n\t" "orl $0x100, (%%esp) \n\t" "popfl \n\t" "nop \n\t" "nop \n\t" "outb %b0, %w1 \n\t" "nop \n\t" <--- Not getting Debug Trap before executing this "nop \n\t" "pushfl \n\t" "xorl $0x100, (%%esp) \n\t" "popfl \n\t" :: "a"(2), "Nd" (80) ); Debug handler simply prints the EIP from interrupt frame and I don't see the EIP of marked instruction. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #15 from Paolo Bonzini --- > if I use gdb in a guest OS, like to debug a program inside the Guest OS, and > run the single step command in gdb, that should trigger this bug right Yes. For kvm-unit-tests you would modify x86/debug.c, which already tests singlestep. Jatin, can you confirm that _any_ single-stepping over sti triggers the bug? Does it matter if IF=0 or IF=1 before the sti? -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #16 from Jidong Xiao --- Alright, thank you Paolo, I will try and let you know once I am done.(In reply to Paolo Bonzini from comment #15) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561
--- Comment #17 from Jidong Xiao ---
Hi,Paolo,
I am not familiar with kvm-unit-tests, and I cannot find any documents describe
it. So I use gdb to debug.
And yes I can reproduce the problem. I just use Jatin's sample code to
construct a c program, like this:
linux:~/code/cvedr # cat ss.c
#include
main(){
asm __volatile__(
"pushfl \n\t"
"orl $0x100, (%%esp) \n\t"
"popfl \n\t"
"nop \n\t"
"nop \n\t"
"outb %b0, %w1 \n\t"
"nop \n\t"
"nop \n\t"
"pushfl \n\t"
"xorl $0x100, (%%esp) \n\t"
"popfl \n\t"
:: "a"(2), "Nd" (80)
);
}
And I ran the c program with gdb.
(gdb) disas main
Dump of assembler code for function main:
0x080483e4 <+0>: push %ebp
0x080483e5 <+1>: mov%esp,%ebp
0x080483e7 <+3>: mov$0x2,%eax
0x080483ec <+8>: pushf
0x080483ed <+9>: orl$0x100,(%esp)
0x080483f4 <+16>:popf
0x080483f5 <+17>:nop
0x080483f6 <+18>:nop
=> 0x080483f7 <+19>:out%al,$0x50
0x080483f9 <+21>:nop
0x080483fa <+22>:nop
0x080483fb <+23>:pushf
0x080483fc <+24>:xorl $0x100,(%esp)
0x08048403 <+31>:popf
0x08048404 <+32>:pop%ebp
0x08048405 <+33>:ret
End of assembler dump.
(gdb) nexti
Program received signal SIGSEGV, Segmentation fault.
0x080483f7 in main ()
(gdb)
You can see when the program counter points to the out instruction, and I used
nexti command to do single step execution, and it ends up a segmentation fault.
According to the kvm code, it seems that x86_emulate_insn() will be called,
indeed I don't see any code in that function takes care of the out instruction.
But why this only affect single step execution? I actually have some other
program that includes some out instructions, and the program runs okay.
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[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561
--- Comment #18 from Jidong Xiao ---
Hi, Paolo,
I am still reading the source code so as to understand the root cause of this
problem. In particular, I added some printk statements in x86_emulate_insn().
For example, I added the following printk statement.
...
switch (c->b) {
case 0x00 ... 0x05:
printk(KERN_ERR "DEBUG: Passed %s %d
\n",__FUNCTION__,__LINE__);
add: /* add */
emulate_2op_SrcV("add", c->src, c->dst, ctxt->eflags);
break;
...
And then in the guest OS, I run a c program like this:
linux:~/code/testc # cat test.c
#include
int main(void)
{
int foo = 10, bar = 15;
__asm__ __volatile__("add %%ebx,%%eax"
:"=a"(foo)
:"a"(foo), "b"(bar)
);
printf("foo+bar=%d\n", foo);
return 0;
}
I thought that because I am using the "add" instruction, the printk statement
in the host os kernel should be invoked, however, my experimental result prove
it's untrue. So I am totally confused with this kvm emulator.
If the kvm trying to emulate these instructions, why that, when I run these
instructions in the guest, the corresponding emulate code are not invoked? So
how to trigger this printk statement? Thanks.
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[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #19 from Jatin Kumar --- I am not sure if I am correct but `add` doesn't look like any privileged or special instruction so if running with KVM it should run directly on the hardware and without needing emulation. You can try some privilege instructions like wrmsr, rdmsr etc. Please correct me if I am wrong. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561
--- Comment #20 from Jidong Xiao ---
Thanks Jatin, I actually tried some other instructions, like accessing cr
register. I use the following program:
linux:~/code/cvedr # cat getcr.c
#include
main(){
asm __volatile__ (
"mov %cr0, %eax\n"
"mov %cr3, %ebx\n"
);
printf("test cr\n");
}
In x86_emulate_insn(), there is a piece of code like this (the printk is added
by me.)
==
case 0x20: /* mov cr, reg */
printk(KERN_ERR "DEBUG: Passed %s %d
\n",__FUNCTION__,__LINE__);
if (c->modrm_mod != 3)
goto cannot_emulate;
c->regs[c->modrm_rm] =
realmode_get_cr(ctxt->vcpu, c->modrm_reg);
c->dst.type = OP_NONE; /* no writeback */
break;
==
My results show that the above c program does not trigger this printk statement
neither. I assume accessing cr should be a privileged operation, right? So I am
really curious that how to trigger these printk statements?
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[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #21 from Jatin Kumar --- The way I would approach this problem is to first check if there is a VM_EXIT while executing this instruction. You should be able to find that in vmx_vcpu_run() function (I guess in KVM code). Put a printk there and print the instruction as well which caused VM_EXIT. Futher you should try to investigate if the control flow is trying to emulate this instruction and then your printk's should be triggered. CAUTION: I haven't spent much time digging KVM code, but I am confident about the VM_EXIT part. Still after putting in some effort, you may want to wait for Paolo's reply :) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561
--- Comment #22 from Jidong Xiao ---
Alright, I added a printk statement in the wrmsr case, like this:
case 0x30:
printk(KERN_ERR "DEBUG: Passed %s %d
\n",__FUNCTION__,__LINE__);
/* wrmsr */
msr_data = (u32)c->regs[VCPU_REGS_RAX]
| ((u64)c->regs[VCPU_REGS_RDX] << 32);
rc = kvm_set_msr(ctxt->vcpu, c->regs[VCPU_REGS_RCX], msr_data);
if (rc) {
kvm_inject_gp(ctxt->vcpu, 0);
c->eip = kvm_rip_read(ctxt->vcpu);
}
rc = X86EMUL_CONTINUE;
c->dst.type = OP_NONE;
break;
And i run a c program to access msr, like this:
linux:~/code/cvedr # cat accessmsr.c
#include
main(){
asm volatile("wrmsr");
printf("test msr\n");
}
linux:~/code/cvedr # ./accessmsr
Segmentation fault
Even though my c program in the guest os got a segmentation fault, from the
host os level, I don't see the printk statement is triggered, so this is not
about privileged instructions or unprivileged instructions. I think there must
be some other conditions to trigger these printk statements.
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[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #23 from Jidong Xiao --- Jatin, do you mean that if one instruction triggers a VM_EXIT, then it won't trigger the emulate code? So why the emulate code tries to emulate those privileged instructions, like wrmsr, rdmsr, mov cr to reg, mov dr to reg, I think these instructions will trigger VM_EXIT anyway, but we see the kvm emulator still attempt to emulate them. (In reply to Jatin Kumar from comment #21) > The way I would approach this problem is to first check if there is a > VM_EXIT while executing this instruction. You should be able to find that in > vmx_vcpu_run() function (I guess in KVM code). Put a printk there and print > the instruction as well which caused VM_EXIT. > > Futher you should try to investigate if the control flow is trying to > emulate this instruction and then your printk's should be triggered. > > CAUTION: I haven't spent much time digging KVM code, but I am confident > about the VM_EXIT part. Still after putting in some effort, you may want to > wait for Paolo's reply :) -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #24 from Jatin Kumar --- > linux:~/code/cvedr # ./accessmsr > Segmentation fault You got a seg fault because it is privileged instruction and I run it in kernel mode not user mode. But you are likely to be running your program in user mode. Try something like out instruction. > Even though my c program in the guest os got a segmentation fault, from the > host os level, I don't see the printk statement is triggered, so this is not > about privileged instructions or unprivileged instructions. I think there > must be some other conditions to trigger these printk statements. After getting the VM_EXIT it must be first checking if it requires to emulate or should generate a fault. In this case it would have generated the fault without emulating it. Again, you can try it with 'out' instruction. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561
--- Comment #25 from Jidong Xiao ---
(In reply to Jatin Kumar from comment #24)
> > linux:~/code/cvedr # ./accessmsr
> > Segmentation fault
> You got a seg fault because it is privileged instruction and I run it in
> kernel mode not user mode. But you are likely to be running your program in
> user mode. Try something like out instruction.
>
> > Even though my c program in the guest os got a segmentation fault, from the
> > host os level, I don't see the printk statement is triggered, so this is not
> > about privileged instructions or unprivileged instructions. I think there
> > must be some other conditions to trigger these printk statements.
> After getting the VM_EXIT it must be first checking if it requires to
> emulate or should generate a fault. In this case it would have generated the
> fault without emulating it.
>
> Again, you can try it with 'out' instruction.
Alright, Jatin, I wrote a kernel module, like this:
linux:~/code/module # cat testout.c
#include
#include
int init_module(void)
{
printk(KERN_ALERT "Hello world 1.\n");
asm __volatile__("outb %al, %dx \n");
return 0;
}
void cleanup_module(void)
{
printk(KERN_ALERT "Goodbye world 1.\n");
}
I compiled this module and installed with `insmod testout.ko`, and nothing
happens. Noted that the emulator code includes the following lines:
case 0xee: /* out al,dx */
case 0xef: /* out (e/r)ax,dx */
printk(KERN_ERR "DEBUG: Passed %s %d
\n",__FUNCTION__,__LINE__);
port = c->regs[VCPU_REGS_RDX];
io_dir_in = 0;
I added that printk statement, and still, when I was loading the kernel module
in the guest OS, this printk statement was not invoked.
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[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #26 from Jatin Kumar --- In arch/x86/kvm/vmx.c file, there is a complete list of kvm_vmx_exit_handlers, you can find there appropriate handlers for each of the exit reasons. There is a handle_io() handler. Can you try adding a printk to this. I am not sure but it may be going to x86_emulate_instruction() which then calls x86_emulate_insn() if required. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #27 from Jidong Xiao --- Jatin, after I have added printk in handle_io, it looks like the printk will be called very frequently, I don't need to run any own program in the guest OS, the printk message in handle_io() is kept showing and never stops. Therefore I cannot tell whether a out instruction would also trigger the emulator or not. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #28 from Paolo Bonzini --- As Jatin said, most of the time the emulator is not invoked for instructions that require intervention of the hypervisor. Instead, the processor provides enough "pre-decoded" information about the instruction, so KVM doesn't need to do it all again in the emulator. Instructions that invoke the emulator are those that invoke ports or memory-mapped devices. However "out" is a fast path, so it doesn't invoke the emulator. You see it all the time because the kernel uses it to interact with many devices (such as the keyboard controller, disk controller or network cards). I suggest that you try reproducing the problem with "sti". The one with "out" is known and documented in the source code. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #29 from Jidong Xiao --- Okay, I will try the sti instruction. Jatin, since your title says that there is something wrong with the sti instruction, but looking at your sample code, it does not include a sti instruction, and all you were talking about is the "out" instruction. So you are reporting two different problems or it's just one problem? -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #30 from Jidong Xiao --- Jatin, I have the following program and I did test the single step for sti command, (gdb) disas main Dump of assembler code for function main: 0x08048414 <+0>: push %ebp 0x08048415 <+1>: mov%esp,%ebp 0x08048417 <+3>: and$0xfff0,%esp 0x0804841a <+6>: sub$0x10,%esp => 0x0804841d <+9>: sti 0x0804841e <+10>:movl $0x8048500,(%esp) 0x08048425 <+17>:call 0x8048350 0x0804842a <+22>:leave 0x0804842b <+23>:ret End of assembler dump. (gdb) nexti Program received signal SIGSEGV, Segmentation fault. 0x0804841d in main () (gdb) And what I have got is a segmentation fault. Since you said you triggered the bug via a kernel module, how did you do the single step test for a kernel module? In the meanwhile I am studying kvm-unit-test, since Paolo said it provides a single step test platform. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561
--- Comment #31 from Jidong Xiao ---
Hi, Paolo,
I added a sti instruction in kvm-unit-tests:x86/debug.c, like this:
asm volatile(
"pushf\n\t"
"pop %%rax\n\t"
"sti\n\t"
"or $(1<<8),%%rax\n\t"
"push %%rax\n\t"
"lea (%%rip),%0\n\t"
"popf\n\t"
"and $~(1<<8),%%rax\n\t"
"push %%rax\n\t"
"popf\n\t"
: "=g" (start) : : "rax");
report("single step",
n == 3 &&
bp_addr[0] == start+1+6 && dr6[0] == 0x4ff0 &&
bp_addr[1] == start+1+6+1 && dr6[1] == 0x4ff0 &&
bp_addr[2] == start+1+6+1+1 && dr6[2] == 0x4ff0);
And then make, and run the test, it looks like everything is okay.
linux:~/code/kvm-unit-tests # /usr/local2/bin/qemu-system-x86_64 -enable-kvm
-device pc-testdev -serial stdio -device isa-debug-exit,iobase=0xf4,iosize=0x4
-kernel ./x86/debug.flat
enabling apic
PASS: #BP
PASS: hw breakpoint
PASS: single step
PASS: hw watchpoint
I also tried to add a cli before sti, and the test also passed.
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[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #32 from Jatin Kumar --- (In reply to Jidong Xiao from comment #29) > Okay, I will try the sti instruction. > > Jatin, since your title says that there is something wrong with the sti > instruction, but looking at your sample code, it does not include a sti > instruction, and all you were talking about is the "out" instruction. So you > are reporting two different problems or it's just one problem? Hello Jidong, I am sorry for the confusion. Yes these are two independent problems. 1. Single stepping an STI instruction (which as you said is already fixed) 2. Single stepping an OUT instruction, which works but causes the next instruction to be executed without debug trap. I am developing a small OS which runs in kernel mode most of the time and I need to single step the code to a particular point in execution. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #33 from Jidong Xiao --- Jatin, thanks for the clarification. Are you using kgdb to perform single step kernel code? I am still wondering how did you do the single step execution for kernel level code. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[Bug 65561] KVM:Entry failed on Single stepping sti instruction
https://bugzilla.kernel.org/show_bug.cgi?id=65561 --- Comment #34 from Jatin Kumar --- (In reply to Jidong Xiao from comment #33) > Jatin, thanks for the clarification. Are you using kgdb to perform single > step kernel code? I am still wondering how did you do the single step > execution for kernel level code. As I mentioned its not a full fledge operating system, just a dummy one. So I just set the DEBUG TRAP flag in eflags before the code section I want to single step and disable it after wards. And in the interrupt handler I have some simple code (say printf) for handling the single step debug interrupt. -- You are receiving this mail because: You are watching the assignee of the bug. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
