Gleb Natapov wrote: > On Sat, Feb 13, 2010 at 10:31:12AM +0100, Jan Kiszka wrote: >> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >> >> We intercept #BP while in guest debugging mode. As VM exists 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. >> > event_exit_inst_len is only used for event reinjection. Since event > intercepted here will not be reinjected why updating event_exit_inst_len > is needed here? In guest debugging mode a #BP exception is always reported to user space to find out what caused it. If it was the guest itself, the exception is reinjected, on older kernels via KVM_SET_GUEST_DEBUG and since 2.6.33 via KVM_SET_VCPU_EVENTS (the latter requires some qemu patch that I will post later). As we currently do not update event_exit_inst_len on #BP exits, reinjecting fails unless event_exit_inst_len happens to be 1 from some other exit. Jan > >> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >> --- >> >> Please consider for stable, this fixes guest debugging scenarios. >> >> arch/x86/kvm/vmx.c | 4 ++++ >> 1 files changed, 4 insertions(+), 0 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index f82b072..e9f64e8 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -2775,6 +2775,8 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu, >> kvm_queue_exception(vcpu, vec); >> return 1; >> case BP_VECTOR: >> + 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 +2899,8 @@ static int handle_exception(struct kvm_vcpu *vcpu) >> kvm_run->debug.arch.dr7 = vmcs_readl(GUEST_DR7); >> /* fall through */ >> case BP_VECTOR: >> + 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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