linux-kernel - Re: [RFC PATCH 10/18] KVM: VMX: Extend EPT Violation protection bits

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Message-ID: <aCI_0WqSzrgtz6IW@google.com>
Date: Mon, 12 May 2025 11:37:05 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jon Kohler <jon@...anix.com>
Cc: pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 10/18] KVM: VMX: Extend EPT Violation protection bits

On Thu, Mar 13, 2025, Jon Kohler wrote:
> Define macros for READ, WRITE, EXEC protection bits, to be used by
> MBEC-enabled systems.
> 
> No functional change intended.
> 
> Signed-off-by: Jon Kohler <jon@...anix.com>
> 
> ---
>  arch/x86/include/asm/vmx.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> index d7ab0ad63be6..ffc90d672b5d 100644
> --- a/arch/x86/include/asm/vmx.h
> +++ b/arch/x86/include/asm/vmx.h
> @@ -593,8 +593,17 @@ enum vm_entry_failure_code {
>  #define EPT_VIOLATION_GVA_IS_VALID	BIT(7)
>  #define EPT_VIOLATION_GVA_TRANSLATED	BIT(8)
>  
> +#define EPT_VIOLATION_READ_TO_PROT(__epte) (((__epte) & VMX_EPT_READABLE_MASK) << 3)
> +#define EPT_VIOLATION_WRITE_TO_PROT(__epte) (((__epte) & VMX_EPT_WRITABLE_MASK) << 3)
> +#define EPT_VIOLATION_EXEC_TO_PROT(__epte) (((__epte) & VMX_EPT_EXECUTABLE_MASK) << 3)
>  #define EPT_VIOLATION_RWX_TO_PROT(__epte) (((__epte) & VMX_EPT_RWX_MASK) << 3)
>  
> +static_assert(EPT_VIOLATION_READ_TO_PROT(VMX_EPT_READABLE_MASK) ==
> +	      (EPT_VIOLATION_PROT_READ));
> +static_assert(EPT_VIOLATION_WRITE_TO_PROT(VMX_EPT_WRITABLE_MASK) ==
> +	      (EPT_VIOLATION_PROT_WRITE));
> +static_assert(EPT_VIOLATION_EXEC_TO_PROT(VMX_EPT_EXECUTABLE_MASK) ==
> +	      (EPT_VIOLATION_PROT_EXEC));

Again, as a general rule, introduce macros and helpers functions when they are
first used, not as tiny prep patches.  There are exceptions to that rule, e.g. to
avoid cyclical dependencies or to isolate arch/vendor changes, but know of those
exceptions apply in this series.

Patches like this are effectively impossible to review from a design/intent
perspective, because without peeking at the usage that comes along later, there's
no way to determine whether or not it makes sense to add these macros.

And looking ahead, I don't see any reason to slice n' dice the RWX=>prot macro.

TL;DR: drop this patch.