Re: [PATCH v5 09/12] Retry fault before vmentry

Avi Kivity
2010-08-24T09:39:14Z

On 08/24/2010 12:33 PM, Gleb Natapov wrote:
>
>
>>> @@ -505,6 +506,37 @@ out_unlock:
>>> return 0;
>>> }
>>>
>>> +static int FNAME(page_fault_other_cr3)(struct kvm_vcpu *vcpu, gpa_t cr3,
>>> + gva_t addr, u32 error_code)
>>> +{
>>> + int r = 0;
>>> + gpa_t curr_cr3 = vcpu->arch.cr3;
>>> +
>>> + if (curr_cr3 != cr3) {
>>> + /*
>>> + * We do page fault on behalf of a process that is sleeping
>>> + * because of async PF. PV guest takes reference to mm that cr3
>>> + * belongs too, so it has to be valid here.
>>> + */
>>> + kvm_set_cr3(vcpu, cr3);
>>> + if (kvm_mmu_reload(vcpu))
>>> + goto switch_cr3;
>>> + }
>> With nested virtualization, we need to switch cr0, cr4, and efer as well...
>>
> On SVM or VMX or both?

Both. Let's defer this patch since it's an optimization, this is really
complicated.

>>> +
>>> + r = FNAME(page_fault)(vcpu, addr, error_code, true);
>>> +
>>> + if (kvm_check_request(KVM_REQ_MMU_SYNC, vcpu))
>>> + kvm_mmu_sync_roots(vcpu);
>> Why is this needed?
>>
> http://www.mail-archive.com/kvm@vger.kernel.org/msg37827.html
>
> KVM_REQ_MMU_SYNC request generated here must be processed before
> switching to a different cr3 (otherwise vcpu_enter_guest will process it
> with the wrong cr3 in place).

Ah, it should be part of the cr3 switch block above.

>>> +
>>> +switch_cr3:
>>> + if (curr_cr3 != vcpu->arch.cr3) {
>>> + kvm_set_cr3(vcpu, curr_cr3);
>>> + kvm_mmu_reload(vcpu);
>>> + }
>>> +
>>> + return r;
>>> +}
>> This has the nasty effect of flushing the TLB on AMD.
>>
> What is more expansive reenter the guest and handle one more fault, or
> flash TLB here?

No idea. Probably the reentry. On Intel the tlb is flushed anyway.

--
error compiling committee.c: too many arguments to function