> On 13 Nov 2019, at 17:17, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 12/11/19 19:33, Liran Alon wrote:
>> When KVM emulates a nested VMEntry (L1->L2 VMEntry), it switches mmu root
>> page. If nEPT is used, this will happen from
>> kvm_init_shadow_ept_mmu()->__kvm_mmu_new_cr3() and otherwise it will
>> happpen from nested_vmx_load_cr3()->kvm_mmu_new_cr3(). Either case,
>> __kvm_mmu_new_cr3() will use fast_cr3_switch() in attempt to switch to a
>> previously cached root page.
>>
>> In case fast_cr3_switch() finds a matching cached root page, it will
>> set it in mmu->root_hpa and request KVM_REQ_LOAD_CR3 such that on
>> next entry to guest, KVM will set root HPA in appropriate hardware
>> fields (e.g. vmcs->eptp). In addition, fast_cr3_switch() calls
>> kvm_x86_ops->tlb_flush() in order to flush TLB as MMU root page
>> was replaced.
>>
>> This works as mmu->root_hpa, which vmx_flush_tlb() use, was
>> already replaced in cached_root_available(). However, this may
>> result in unnecessary INVEPT execution because a KVM_REQ_TLB_FLUSH
>> may have already been requested. For example, by prepare_vmcs02()
>> in case L1 don't use VPID.
>>
>> Therefore, change fast_cr3_switch() to just request TLB flush on
>> next entry to guest.
>>
>> Reviewed-by: Bhavesh Davda <bhavesh.davda@xxxxxxxxxx>
>> Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
>> ---
>> arch/x86/kvm/mmu.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>> index 24c23c66b226..150d982ec1d2 100644
>> --- a/arch/x86/kvm/mmu.c
>> +++ b/arch/x86/kvm/mmu.c
>> @@ -4295,7 +4295,7 @@ static bool fast_cr3_switch(struct kvm_vcpu *vcpu, gpa_t new_cr3,
>> kvm_make_request(KVM_REQ_LOAD_CR3, vcpu);
>> if (!skip_tlb_flush) {
>> kvm_make_request(KVM_REQ_MMU_SYNC, vcpu);
>> - kvm_x86_ops->tlb_flush(vcpu, true);
>> + kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>> }
>>
>> /*
>>
>
> Queued, thanks.
>
> (I should get kvm/queue properly tested and pushed by the end of this week).
>
> Paolo
>
Thanks.
Also note that I have sent another trivial patch that didn’t got any response ("KVM: VMX: Consume pending LAPIC INIT event when exit on INIT_SIGNAL”).
See: https://patchwork.kernel.org/patch/11236869/
I have also sent kvm-unit-tests for my recent patches (The INIT_SIGNAL fix and nVMX TPR-Threshold issue).
See: https://patchwork.kernel.org/patch/11236951/ and https://patchwork.kernel.org/patch/11236961/
-Liran
