linux-kernel - Re: [PATCH MANUALSEL 5.15 2/8] KVM: X86: Don't reset mmu context when X86_CR4

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Date:   Wed, 24 Nov 2021 08:24:48 +0800
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH MANUALSEL 5.15 2/8] KVM: X86: Don't reset mmu context when
 X86_CR4_PCIDE 1->0

Hello,

[PATCH MANUALSEL 5.15 2/8] KVM: X86: Don't reset mmu context when X86_CR4_PCIDE 1->0
[PATCH MANUALSEL 5.15 3/8] KVM: X86: Don't check unsync if the original spte is writible

are pure cleanups, they don't need to backport to stable.

Thanks
Lai

On 2021/11/24 00:36, Sasha Levin wrote:
> From: Lai Jiangshan <laijs@...ux.alibaba.com>
> 
> [ Upstream commit 552617382c197949ff965a3559da8952bf3c1fa5 ]
> 
> X86_CR4_PCIDE doesn't participate in kvm_mmu_role, so the mmu context
> doesn't need to be reset.  It is only required to flush all the guest
> tlb.
> 
> Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
> Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> Message-Id: <20210919024246.89230-2-jiangshanlai@...il.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>   arch/x86/kvm/x86.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 0644f429f848c..98a0f3c28caec 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1042,9 +1042,10 @@ EXPORT_SYMBOL_GPL(kvm_is_valid_cr4);
>   
>   void kvm_post_set_cr4(struct kvm_vcpu *vcpu, unsigned long old_cr4, unsigned long cr4)
>   {
> -	if (((cr4 ^ old_cr4) & KVM_MMU_CR4_ROLE_BITS) ||
> -	    (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
> +	if ((cr4 ^ old_cr4) & KVM_MMU_CR4_ROLE_BITS)
>   		kvm_mmu_reset_context(vcpu);
> +	else if (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE))
> +		kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
>   }
>   EXPORT_SYMBOL_GPL(kvm_post_set_cr4);
>   
>