On Mon, Feb 15, 2010 at 07:17:17PM +0100, Jan Kiszka wrote:
> When in guest debugging mode, we have to reinject those #BP software
> exceptions that are caused by guest-injected INT3. As older AMD
> processors to not support the required nRIP VMCB field, try to emulate
> it by moving RIP by one on injection. Fix it up again in case the
> injection failed and we were able to catch this. This does not work for
> unintercepted faults, but it is better than doing nothing.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> ---
> arch/x86/kvm/svm.c | 54 +++++++++++++++++++++++++++++++++++----------------
> 1 files changed, 37 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 52f78dd..f63f1db 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -46,6 +46,7 @@ MODULE_LICENSE("GPL");
> #define SVM_FEATURE_NPT (1 << 0)
> #define SVM_FEATURE_LBRV (1 << 1)
> #define SVM_FEATURE_SVML (1 << 2)
> +#define SVM_FEATURE_NRIP (1 << 3)
> #define SVM_FEATURE_PAUSE_FILTER (1 << 10)
>
> #define NESTED_EXIT_HOST 0 /* Exit handled on host level */
> @@ -109,6 +110,8 @@ struct vcpu_svm {
> struct nested_state nested;
>
> bool nmi_singlestep;
> +
> + bool int3_injected;
> };
>
> /* enable NPT for AMD64 and X86 with PAE */
> @@ -234,23 +237,6 @@ static void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
> vcpu->arch.efer = efer;
> }
>
> -static void svm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
> - bool has_error_code, u32 error_code)
> -{
> - struct vcpu_svm *svm = to_svm(vcpu);
> -
> - /* If we are within a nested VM we'd better #VMEXIT and let the
> - guest handle the exception */
> - if (nested_svm_check_exception(svm, nr, has_error_code, error_code))
> - return;
> -
> - svm->vmcb->control.event_inj = nr
> - | SVM_EVTINJ_VALID
> - | (has_error_code ? SVM_EVTINJ_VALID_ERR : 0)
> - | SVM_EVTINJ_TYPE_EXEPT;
> - svm->vmcb->control.event_inj_err = error_code;
> -}
> -
> static int is_external_interrupt(u32 info)
> {
> info &= SVM_EVTINJ_TYPE_MASK | SVM_EVTINJ_VALID;
> @@ -296,6 +282,36 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
> svm_set_interrupt_shadow(vcpu, 0);
> }
>
> +static void svm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
> + bool has_error_code, u32 error_code)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> +
> + /* If we are within a nested VM we'd better #VMEXIT and let the
> + guest handle the exception */
> + if (nested_svm_check_exception(svm, nr, has_error_code, error_code))
> + return;
> +
> + if (nr == BP_VECTOR && !svm_has(SVM_FEATURE_NRIP)) {
> + /*
> + * For guest debugging where we have to reinject #BP if some
> + * INT3 is guest-owned:
> + * Emulate nRIP by moving RIP one forward. Will fail if
> + * injection raises a fault that is not intercepted. Still
> + * better than failing in all cases.
> + */
> + svm->next_rip = kvm_rip_read(&svm->vcpu) + 1;
> + skip_emulated_instruction(&svm->vcpu);
if next_rip is zero skip_emulated_instruction() decodes instruction by
itself to properly calculate next rip so no need to guess instruction
length.
> + svm->int3_injected = true;
> + }
> +
> + svm->vmcb->control.event_inj = nr
> + | SVM_EVTINJ_VALID
> + | (has_error_code ? SVM_EVTINJ_VALID_ERR : 0)
> + | SVM_EVTINJ_TYPE_EXEPT;
> + svm->vmcb->control.event_inj_err = error_code;
> +}
> +
> static int has_svm(void)
> {
> const char *msg;
> @@ -2653,6 +2669,9 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)
> if (is_nested(svm))
> break;
> if (kvm_exception_is_soft(vector))
> + if (vector == BP_VECTOR && svm->int3_injected)
> + kvm_rip_write(&svm->vcpu,
> + kvm_rip_read(&svm->vcpu) - 1);
You don't even check current rip? So if fault happens during unrelated #BP you move
rip backwards and restart.
> break;
> if (exitintinfo & SVM_EXITINTINFO_VALID_ERR) {
> u32 err = svm->vmcb->control.exit_int_info_err;
> @@ -2667,6 +2686,7 @@ static void svm_complete_interrupts(struct vcpu_svm *svm)
> default:
> break;
> }
> + svm->int3_injected =false;
Looks like the wrong place to clear this. It should be cleared on every
exit, not only with valid vectoring info.
> }
>
> #ifdef CONFIG_X86_64
> --
> 1.6.0.2
--
Gleb.
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