On 18/07/19 03:36, Josh Poimboeuf wrote: > After making a change to improve objtool's sibling call detection, it > started showing the following warning: > > arch/x86/kvm/vmx/nested.o: warning: objtool: .fixup+0x15: sibling call from > callable instruction with modified stack frame > > The problem is the ____kvm_handle_fault_on_reboot() macro. It does a > fake call by pushing a fake RIP and doing a jump. That tricks the > unwinder into printing the function which triggered the exception, > rather than the .fixup code. > > Instead of the hack to make it look like the original function made the > call, just change the macro so that the original function actually does > make the call. This allows removal of the hack, and also makes objtool > happy. > > I triggered a vmx instruction exception and verified that the stack > trace is still sane: > > kernel BUG at arch/x86/kvm/x86.c:358! > invalid opcode: 0000 [#1] SMP PTI > CPU: 28 PID: 4096 Comm: qemu-kvm Not tainted 5.2.0+ #16 > Hardware name: Lenovo THINKSYSTEM SD530 -[7X2106Z000]-/-[7X2106Z000]-, BIOS > -[TEE113Z-1.00]- 07/17/2017 > RIP: 0010:kvm_spurious_fault+0x5/0x10 > Code: 00 00 00 00 00 8b 44 24 10 89 d2 45 89 c9 48 89 44 24 10 8b 44 24 08 > 48 89 44 24 08 e9 d4 40 22 00 0f 1f 40 00 0f 1f 44 00 00 <0f> 0b 66 0f 1f 84 > 00 00 00 00 00 0f 1f 44 00 00 41 55 49 89 fd 41 > RSP: 0018:ffffbf91c683bd00 EFLAGS: 00010246 > RAX: 000061f040000000 RBX: ffff9e159c77bba0 RCX: ffff9e15a5c87000 > RDX: 0000000665c87000 RSI: ffff9e15a5c87000 RDI: ffff9e159c77bba0 > RBP: 0000000000000000 R08: 0000000000000000 R09: ffff9e15a5c87000 > R10: 0000000000000000 R11: fffff8f2d99721c0 R12: ffff9e159c77bba0 > R13: ffffbf91c671d960 R14: ffff9e159c778000 R15: 0000000000000000 > FS: 00007fa341cbe700(0000) GS:ffff9e15b7400000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fdd38356804 CR3: 00000006759de003 CR4: 00000000007606e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > PKRU: 55555554 > Call Trace: > loaded_vmcs_init+0x4f/0xe0 > alloc_loaded_vmcs+0x38/0xd0 > vmx_create_vcpu+0xf7/0x600 > kvm_vm_ioctl+0x5e9/0x980 > ? __switch_to_asm+0x40/0x70 > ? __switch_to_asm+0x34/0x70 > ? __switch_to_asm+0x40/0x70 > ? __switch_to_asm+0x34/0x70 > ? free_one_page+0x13f/0x4e0 > do_vfs_ioctl+0xa4/0x630 > ksys_ioctl+0x60/0x90 > __x64_sys_ioctl+0x16/0x20 > do_syscall_64+0x55/0x1c0 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > RIP: 0033:0x7fa349b1ee5b > > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> > Acked-by: Paolo Bonzini <pbonz...@redhat.com> > Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org> > --- > v2: Fix ____kvm_handle_fault_on_reboot() comment [Paolo] > > Cc: Paolo Bonzini <pbonz...@redhat.com> > Cc: Radim Krčmář <rkrc...@redhat.com> > --- > arch/x86/include/asm/kvm_host.h | 34 ++++++++++++++++++--------------- > 1 file changed, 19 insertions(+), 15 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 0cc5b611a113..8282b8d41209 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1496,25 +1496,29 @@ enum { > #define kvm_arch_vcpu_memslots_id(vcpu) ((vcpu)->arch.hflags & HF_SMM_MASK ? > 1 : 0) > #define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, (role).smm) > > +asmlinkage void __noreturn kvm_spurious_fault(void); > + > /* > * Hardware virtualization extension instructions may fault if a > * reboot turns off virtualization while processes are running. > - * Trap the fault and ignore the instruction if that happens. > + * Usually after catching the fault we just panic; during reboot > + * instead the instruction is ignored. > */ > -asmlinkage void kvm_spurious_fault(void); > - > -#define ____kvm_handle_fault_on_reboot(insn, cleanup_insn) \ > - "666: " insn "\n\t" \ > - "668: \n\t" \ > - ".pushsection .fixup, \"ax\" \n" \ > - "667: \n\t" \ > - cleanup_insn "\n\t" \ > - "cmpb $0, kvm_rebooting \n\t" \ > - "jne 668b \n\t" \ > - __ASM_SIZE(push) " $666b \n\t" \ > - "jmp kvm_spurious_fault \n\t" \ > - ".popsection \n\t" \ > - _ASM_EXTABLE(666b, 667b) > +#define ____kvm_handle_fault_on_reboot(insn, cleanup_insn) \ > + "666: \n\t" \ > + insn "\n\t" \ > + "jmp 668f \n\t" \ > + "667: \n\t" \ > + "call kvm_spurious_fault \n\t" \ > + "668: \n\t" \ > + ".pushsection .fixup, \"ax\" \n\t" \ > + "700: \n\t" \ > + cleanup_insn "\n\t" \ > + "cmpb $0, kvm_rebooting\n\t" \ > + "je 667b \n\t" \ > + "jmp 668b \n\t" \ > + ".popsection \n\t" \ > + _ASM_EXTABLE(666b, 700b) > > #define __kvm_handle_fault_on_reboot(insn) \ > ____kvm_handle_fault_on_reboot(insn, "") >
Acked-by: Paolo Bonzini <pbonz...@redhat.com> This has a side effect of adding a jump in a generally hot path, but let's hope that the speculation gods for once help us. Paolo