Gleb Natapov wrote: > On Mon, Feb 15, 2010 at 03:53:04PM +0100, Jan Kiszka wrote: >> We intercept #BP while in guest debugging mode. As VM exits due to >> intercepted exceptions do not necessarily come with valid >> idt_vectoring, we have to update event_exit_inst_len explicitly in such >> cases. At least in the absence of migration, this ensures that >> re-injections of #BP will find and use the correct instruction length. >> > Thinking about it some more. Why do we exit to userspace at all if we > intercept wrong #DB? It seams to me not wise to have ability to inject > exceptions from userspace. Exceptions generation mechanism is a part of > CPU and we shouldn't outsource part of CPU functionality to userspace.
The guest debugging API was design to avoid maintaining a "countless" number of breakpoints in kernel space and instead chose to loop over user space to decide about #DB & #BP. So this part is required even if we start thinking about an alternative interface in the future. Jan > >> Signed-off-by: Jan Kiszka <jan.kis...@siemens.com> >> --- >> >> Changes in v2: >> - added comments >> >> arch/x86/kvm/vmx.c | 13 +++++++++++++ >> 1 files changed, 13 insertions(+), 0 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index f82b072..14873b9 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -2775,6 +2775,12 @@ static int handle_rmode_exception(struct kvm_vcpu >> *vcpu, >> kvm_queue_exception(vcpu, vec); >> return 1; >> case BP_VECTOR: >> + /* >> + * Update instruction length as we may reinject the exception >> + * from user space while in guest debugging mode. >> + */ >> + to_vmx(vcpu)->vcpu.arch.event_exit_inst_len = >> + vmcs_read32(VM_EXIT_INSTRUCTION_LEN); >> if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) >> return 0; >> /* fall through */ >> @@ -2897,6 +2903,13 @@ static int handle_exception(struct kvm_vcpu *vcpu) >> kvm_run->debug.arch.dr7 = vmcs_readl(GUEST_DR7); >> /* fall through */ >> case BP_VECTOR: >> + /* >> + * Update instruction length as we may reinject #BP from >> + * user space while in guest debugging mode. Reading it for >> + * #DB as well causes no harm, it is not used in that case. >> + */ >> + vmx->vcpu.arch.event_exit_inst_len = >> + vmcs_read32(VM_EXIT_INSTRUCTION_LEN); >> kvm_run->exit_reason = KVM_EXIT_DEBUG; >> kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip; >> kvm_run->debug.arch.exception = ex_no; > > -- > Gleb.
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