linux-kernel - Re: [PATCH] KVM/x86: fix comment that should be user fault

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Message-ID: <Y/eLt4kqKh0G7kKd@google.com>
Date:   Thu, 23 Feb 2023 07:52:23 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Quanfa Fu <quanfafu@...il.com>
Cc:     pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM/x86: fix comment that should be user fault

On Thu, Feb 23, 2023, Quanfa Fu wrote:
> The content of comment should be user fault not read. In order to avoid
> confusion, fix the comment.

No, the existing comment is correct.  Ignoring optional extensions, EPT doesn't
differntiate between Supervisor and User, but does support !READABLE mappings.
And so KVM piggybacks PFERR_USER_MASK to track whether or not an EPT fault occurred
on a read access.

> 
> Signed-off-by: Quanfa Fu <quanfafu@...il.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 7eec0226d56a..3c1012039517 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5668,7 +5668,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
>  	gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
>  	trace_kvm_page_fault(vcpu, gpa, exit_qualification);
>  
> -	/* Is it a read fault? */
> +	/* Is it a user fault? */
>  	error_code = (exit_qualification & EPT_VIOLATION_ACC_READ)
>  		     ? PFERR_USER_MASK : 0;
>  	/* Is it a write fault? */
> -- 
> 2.31.1
> 
>