Re: [PATCH] KVM: VMX: Update instruction length on intercepted BP

Gleb Natapov
2010-02-14T07:53:05Z

On Sat, Feb 13, 2010 at 10:31:12AM +0100, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
>
> 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?

> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>
> 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.