linux-kernel - Re: [PATCH] KVM: x86: Reset MMU context if guest toggles CR4.SMAP or CR4.PKE

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Date:   Fri, 25 Sep 2020 14:56:47 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Peter Shier <pshier@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH] KVM: x86: Reset MMU context if guest toggles CR4.SMAP or
 CR4.PKE

On 23/09/20 23:53, Sean Christopherson wrote:
> Reset the MMU context during kvm_set_cr4() if SMAP or PKE is toggled.
> Recent commits to (correctly) not reload PDPTRs when SMAP/PKE are
> toggled inadvertantly skipped the MMU context reset due to the mask
> of bits that triggers PDPTR loads also being used to trigger MMU context
> resets.
> 
> Fixes: 427890aff855 ("kvm: x86: Toggling CR4.SMAP does not load PDPTEs in PAE mode")
> Fixes: cb957adb4ea4 ("kvm: x86: Toggling CR4.PKE does not load PDPTEs in PAE mode")
> Cc: Jim Mattson <jmattson@...gle.com>
> Cc: Peter Shier <pshier@...gle.com>
> Cc: Oliver Upton <oupton@...gle.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/x86.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 17f4995e80a7..fd0da41bc149 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -977,6 +977,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  	unsigned long old_cr4 = kvm_read_cr4(vcpu);
>  	unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
>  				   X86_CR4_SMEP;
> +	unsigned long mmu_role_bits = pdptr_bits | X86_CR4_SMAP | X86_CR4_PKE;
>  
>  	if (kvm_valid_cr4(vcpu, cr4))
>  		return 1;
> @@ -1004,7 +1005,7 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
>  	if (kvm_x86_ops.set_cr4(vcpu, cr4))
>  		return 1;
>  
> -	if (((cr4 ^ old_cr4) & pdptr_bits) ||
> +	if (((cr4 ^ old_cr4) & mmu_role_bits) ||
>  	    (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
>  		kvm_mmu_reset_context(vcpu);
>  
> 

Queued, thanks.

Paolo