Re: [kvm-devel] [PATCH] Refactor hypercall infrastructure (v2)

Amit Shah
2007-12-02T13:47:41Z

* Anthony Liguori wrote:
> This patch refactors the current hypercall infrastructure to better support
> live migration and SMP. It eliminates the hypercall page by trapping the
> UD exception that would occur if you used the wrong hypercall instruction
> for the underlying architecture and replacing it with the right one lazily.

This doesn't work right for SVM. It keeps looping indefinitely; on a kvm_stat
run, I get about 230,000 light vm exits per second, with the hypercall never
returning to the guest.

...

> diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
> index 729f1cd..d09a9f5 100644
> --- a/drivers/kvm/svm.c
> +++ b/drivers/kvm/svm.c
> @@ -476,7 +476,8 @@ static void init_vmcb(struct vmcb *vmcb)
> INTERCEPT_DR5_MASK |
> INTERCEPT_DR7_MASK;
>
> - control->intercept_exceptions = 1 << PF_VECTOR;
> + control->intercept_exceptions = (1 << PF_VECTOR) |
> + (1 << UD_VECTOR);
>
>
> control->intercept = (1ULL << INTERCEPT_INTR) |
> @@ -970,6 +971,17 @@ static int pf_interception(struct vcpu_svm *svm,
> struct kvm_run *kvm_run) return 0;
> }
>
> +static int ud_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
> +{
> + int er;
> +
> + er = emulate_instruction(&svm->vcpu, kvm_run, 0, 0);
> + if (er != EMULATE_DONE)
> + inject_ud(&svm->vcpu);
> +
> + return 1;
> +}
> +
> static int nm_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
> {
> svm->vmcb->control.intercept_exceptions &= ~(1 << NM_VECTOR);
> @@ -1036,7 +1048,8 @@ static int vmmcall_interception(struct vcpu_svm *svm,
> struct kvm_run *kvm_run) {
> svm->next_rip = svm->vmcb->save.rip + 3;
> skip_emulated_instruction(&svm->vcpu);
> - return kvm_hypercall(&svm->vcpu, kvm_run);
> + kvm_emulate_hypercall(&svm->vcpu);
> + return 1;
> }
>
> static int invalid_op_interception(struct vcpu_svm *svm,
> @@ -1232,6 +1245,7 @@ static int (*svm_exit_handlers[])(struct vcpu_svm
> *svm, [SVM_EXIT_WRITE_DR3] = emulate_on_interception,
> [SVM_EXIT_WRITE_DR5] = emulate_on_interception,
> [SVM_EXIT_WRITE_DR7] = emulate_on_interception,
> + [SVM_EXIT_EXCP_BASE + UD_VECTOR] = ud_interception,
> [SVM_EXIT_EXCP_BASE + PF_VECTOR] = pf_interception,
> [SVM_EXIT_EXCP_BASE + NM_VECTOR] = nm_interception,
> [SVM_EXIT_INTR] = nop_on_interception,
> @@ -1664,7 +1678,6 @@ svm_patch_hypercall(struct kvm_vcpu *vcpu, unsigned
> char *hypercall) hypercall[0] = 0x0f;
> hypercall[1] = 0x01;
> hypercall[2] = 0xd9;
> - hypercall[3] = 0xc3;
> }

...

> +/* This instruction is vmcall. On non-VT architectures, it will generate
> a + * trap that we will then rewrite to the appropriate instruction. */
> -#define __NR_hypercalls 0
> +#define KVM_HYPERCALL ".byte 0x0f,0x01,0xc1"

.. which never happens.