linux-kernel - Re: [PATCH] KVM/MMU: Combine flushing remote tlb in mmu_set

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Date:   Wed, 25 Jul 2018 02:35:16 +0000
From:   Tianyu Lan <Tianyu.Lan@...rosoft.com>
To:     Junaid Shahid <junaids@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>
CC:     "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Subject: Re: [PATCH] KVM/MMU: Combine flushing remote tlb in mmu_set_spte()

Hi Junaid:
	Thanks for your review.

On 7/25/2018 10:26 AM, Junaid Shahid wrote:
> On 07/24/2018 07:35 AM, Paolo Bonzini wrote:
>> On 24/07/2018 10:17, Tianyu Lan wrote:
>>> mmu_set_spte() flushes remote tlbs for drop_parent_pte/drop_spte()
>>> and set_spte() separately. This may introduce redundant flush. This
>>> patch is to combine these flushes and check flush request after
>>> calling set_spte().
>>>
>>> Signed-off-by: Lan Tianyu <Tianyu.Lan@...rosoft.com>
>>
>> Looks good, but I'd like a second opinion.  Guangrong, Junaid, can you
>> review this?
>>
>> Thanks,
>>
>> Paolo
>>
>>> ---
>>>   arch/x86/kvm/mmu.c | 7 ++++---
>>>   1 file changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>>> index 22a7984..8f21632 100644
>>> --- a/arch/x86/kvm/mmu.c
>>> +++ b/arch/x86/kvm/mmu.c
>>> @@ -2901,6 +2901,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep, unsigned pte_access,
>>>   	int rmap_count;
>>>   	int set_spte_ret;
>>>   	int ret = RET_PF_RETRY;
>>> +	bool flush = false;
>>>   
>>>   	pgprintk("%s: spte %llx write_fault %d gfn %llx\n", __func__,
>>>   		 *sptep, write_fault, gfn);
>>> @@ -2917,12 +2918,12 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep, unsigned pte_access,
>>>   
>>>   			child = page_header(pte & PT64_BASE_ADDR_MASK);
>>>   			drop_parent_pte(child, sptep);
>>> -			kvm_flush_remote_tlbs(vcpu->kvm);
>>> +			flush = true;
>>>   		} else if (pfn != spte_to_pfn(*sptep)) {
>>>   			pgprintk("hfn old %llx new %llx\n",
>>>   				 spte_to_pfn(*sptep), pfn);
>>>   			drop_spte(vcpu->kvm, sptep);
>>> -			kvm_flush_remote_tlbs(vcpu->kvm);
>>> +			flush = true;
>>>   		} else
>>>   			was_rmapped = 1;
>>>   	}
>>> @@ -2934,7 +2935,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep, unsigned pte_access,
>>>   			ret = RET_PF_EMULATE;
>>>   		kvm_make_request(KVM_REQ_TLB_FLUSH, vcpu);
>>>   	}
>>> -	if (set_spte_ret & SET_SPTE_NEED_REMOTE_TLB_FLUSH)
>>> +	if (set_spte_ret & SET_SPTE_NEED_REMOTE_TLB_FLUSH || flush)
>>>   		kvm_flush_remote_tlbs(vcpu->kvm);
>>>   
>>>   	if (unlikely(is_mmio_spte(*sptep)))
>>>
>>
> 
> Reviewed-by: Junaid Shahid <junaids@...gle.com>
>