Re: [PATCH v3 20/34] KVM: x86: KVM_REQ_TLB_FLUSH_CURRENT is a superset of KVM_REQ_HV_TLB_FLUSH too

Vitaly Kuznetsov
2022-05-19T09:12:23Z

Maxim Levitsky <mlevitsk@redhat.com> writes:

> On Thu, 2022-04-14 at 15:19 +0200, Vitaly Kuznetsov wrote:
>> KVM_REQ_TLB_FLUSH_CURRENT is an even stronger operation than
>> KVM_REQ_TLB_FLUSH_GUEST so KVM_REQ_HV_TLB_FLUSH needs not to be
>> processed after it.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>> arch/x86/kvm/x86.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index e5aec386d299..d3839e648ab3 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -3357,8 +3357,11 @@ static inline void kvm_vcpu_flush_tlb_current(struct kvm_vcpu *vcpu)
>> */
>> void kvm_service_local_tlb_flush_requests(struct kvm_vcpu *vcpu)
>> {
>> - if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu))
>> + if (kvm_check_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu)) {
>> kvm_vcpu_flush_tlb_current(vcpu);
>> + if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
>> + kvm_hv_vcpu_empty_flush_tlb(vcpu);
>> + }
>>
>> if (kvm_check_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu)) {
>> kvm_vcpu_flush_tlb_guest(vcpu);
>
>
> I think that this patch should be moved near patch 1 and/or even squished with it.
>

Sure, will merge.

This, however, made me think there's room for optimization here. In some
cases, when both KVM_REQ_TLB_FLUSH_CURRENT and KVM_REQ_TLB_FLUSH_GUEST
were requested, there's no need to flush twice, e.g. on SVM
.flush_tlb_current == .flush_tlb_guest. I'll probably not go into this
territory with this series as it's already fairly big, just something
for the future.

--
Vitaly