linux-kernel - Re: [RFC Part2 PATCH 05/30] x86: define RMP violation #PF error code

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Date:   Wed, 24 Mar 2021 11:03:20 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org
Cc:     ak@...ux.intel.com, herbert@...dor.apana.org.au,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <jroedel@...e.de>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC Part2 PATCH 05/30] x86: define RMP violation #PF error code

> diff --git a/arch/x86/include/asm/trap_pf.h b/arch/x86/include/asm/trap_pf.h
> index 10b1de500ab1..107f9d947e8d 100644
> --- a/arch/x86/include/asm/trap_pf.h
> +++ b/arch/x86/include/asm/trap_pf.h
> @@ -12,6 +12,7 @@
>   *   bit 4 ==				1: fault was an instruction fetch
>   *   bit 5 ==				1: protection keys block access
>   *   bit 15 ==				1: SGX MMU page-fault
> + *   bit 31 ==				1: fault was an RMP violation
>   */
>  enum x86_pf_error_code {
>  	X86_PF_PROT	=		1 << 0,
> @@ -21,6 +22,7 @@ enum x86_pf_error_code {
>  	X86_PF_INSTR	=		1 << 4,
>  	X86_PF_PK	=		1 << 5,
>  	X86_PF_SGX	=		1 << 15,
> +	X86_PF_RMP	=		1ull << 31,
>  };

Man, I hope AMD and Intel are talking to each other about these bits.  :)

Either way, this is hitting the limits of what I know about how enums
are implemented.  I had internalized that they are just an 'int', but
that doesn't seem quite right.  It sounds like they must be implemented
using *an* integer type, but not necessarily 'int' itself.

Either way, '1<<31' doesn't fit in a 32-bit signed int.  But, gcc at
least doesn't seem to blow the enum up into a 64-bit type, which is nice.

Could we at least start declaring these with BIT()?