linux-kernel - Re: [PATCH 0/2] KVM: X86: Don't reset mmu context when changing PGE or PCID

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Message-ID: <d2a735cc-4d08-7b87-48b3-5e803f1fdec7@redhat.com>
Date:   Fri, 15 Oct 2021 18:02:11 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Subject: Re: [PATCH 0/2] KVM: X86: Don't reset mmu context when changing PGE
 or PCID

On 14/10/21 18:03, Lai Jiangshan wrote:
> Ping
> 
> On 2021/9/19 10:42, Lai Jiangshan wrote:
>> From: Lai Jiangshan <laijs@...ux.alibaba.com>
>>
>> This patchset uses kvm_vcpu_flush_tlb_guest() instead of 
>> kvm_mmu_reset_context()
>> when X86_CR4_PGE is changed or X86_CR4_PCIDE is changed 1->0.
>>
>> Neither X86_CR4_PGE nor X86_CR4_PCIDE participates in kvm_mmu_role, so
>> kvm_mmu_reset_context() is not required to be invoked.  Only flushing tlb
>> is required as SDM says.
>>
>> The patchset has nothing to do with performance, because the overheads of
>> kvm_mmu_reset_context() and kvm_vcpu_flush_tlb_guest() are the same.  And
>> even in the [near] future, kvm_vcpu_flush_tlb_guest() will be optimized,
>> the code is not in the hot path.
>>
>> This patchset makes the code more clear when to reset the mmu context.
>> And it makes KVM_MMU_CR4_ROLE_BITS consistent with kvm_mmu_role.
>>
>> Lai Jiangshan (2):
>>    KVM: X86: Don't reset mmu context when X86_CR4_PCIDE 1->0
>>    KVM: X86: Don't reset mmu context when toggling X86_CR4_PGE
>>
>>   arch/x86/kvm/mmu.h | 5 ++---
>>   arch/x86/kvm/x86.c | 7 +++++--
>>   2 files changed, 7 insertions(+), 5 deletions(-)
>>
> 

Queued with kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu) replacement, 
thanks.

Paolo