linux-kernel - Re: [PATCH 02/16] KVM: x86: Remove separate "bit" defines for page fault error code masks

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Message-ID: <CABgObfaXQR7WaUwjvBz-1yJN3fyysj1BMyY0S9L3DbizWjgrSQ@mail.gmail.com>
Date: Thu, 29 Feb 2024 21:56:04 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Yan Zhao <yan.y.zhao@...el.com>, Isaku Yamahata <isaku.yamahata@...el.com>, 
	Michael Roth <michael.roth@....com>, Yu Zhang <yu.c.zhang@...ux.intel.com>, 
	Chao Peng <chao.p.peng@...ux.intel.com>, Fuad Tabba <tabba@...gle.com>, 
	David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH 02/16] KVM: x86: Remove separate "bit" defines for page
 fault error code masks

On Thu, Feb 29, 2024 at 7:40 PM Sean Christopherson <seanjc@...gle.com> wrote:
> Long story short, I think we should get to the below (I'll post a separate series,
> assuming I'm not missing something).
>
>         unsigned long rflags = static_call(kvm_x86_get_rflags)(vcpu);
>         unsigned int pfec = access & (PFERR_PRESENT_MASK |
>                                       PFERR_WRITE_MASK |
>                                       PFERR_USER_MASK |
>                                       PFERR_FETCH_MASK);
>
>         /*
>          * For explicit supervisor accesses, SMAP is disabled if EFLAGS.AC = 1.
>          * For implicit supervisor accesses, SMAP cannot be overridden.
>          *
>          * SMAP works on supervisor accesses only, and not_smap can
>          * be set or not set when user access with neither has any bearing
>          * on the result.
>          *
>          * We put the SMAP checking bit in place of the PFERR_RSVD_MASK bit;
>          * this bit will always be zero in pfec, but it will be one in index
>          * if SMAP checks are being disabled.
>          */
>         u64 implicit_access = access & PFERR_IMPLICIT_ACCESS;
>         bool not_smap = ((rflags & X86_EFLAGS_AC) | implicit_access) == X86_EFLAGS_AC;
>         int index = (pfec | (not_smap ? PFERR_RSVD_MASK : 0)) >> 1;
>         u32 errcode = PFERR_PRESENT_MASK;
>         bool fault;

Sounds good.  The whole series is

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>

apart from the small nits that were pointed out here and there.

Paolo