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

Anthony Liguori
2007-12-02T23:03:20Z

Amit Shah wrote:
> * 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.
>
> ...
>

What are you using to issue the hypercall?

Regards,

Anthony Liguori

>> 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.
>