linux-kernel - Re: [PATCH] x86: add additional EPT bit definitions

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Date:   Tue, 25 Jan 2022 00:51:55 -0800
From:   Ayush Ranjan <ayushranjan@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ben Gardon <bgardon@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andrei Vagin <avagin@...il.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Michael Pratt <mpratt@...gle.com>
Subject: Re: [PATCH] x86: add additional EPT bit definitions

Abandoning this patch.

On Mon, Jan 24, 2022 at 9:24 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Sun, Jan 23, 2022, Ayush Ranjan wrote:
> > From: Michael Pratt <mpratt@...gle.com>
> >
> > Used in gvisor for EPT support.
>
> As you may have surmised from the other patch, the changelogs from patches carried
> in our internal kernels rarely meet the criteria for acceptance upstream.  E.g. this
> doesn't provide sufficient justification since there's obviously no in-kernel gvisor
> that's consuming this.
>
> Submitting patches that we carry internally is perfectly ok, but there needs to be
> sufficient justfication, and the patch needs to follow the rules laid out by
> Documentation/process/submitting-patches.rst.
>
> > Tested: Builds cleanly
> > Signed-off-by: Ayush Ranjan <ayushranjan@...gle.com>
> > Signed-off-by: Michael Pratt <mpratt@...gle.com>
> > ---
> >  arch/x86/include/asm/vmx.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> > index 0ffaa3156a4e..c77ad687cdf7 100644
> > --- a/arch/x86/include/asm/vmx.h
> > +++ b/arch/x86/include/asm/vmx.h
> > @@ -496,7 +496,9 @@ enum vmcs_field {
> >  #define VMX_EPT_WRITABLE_MASK                        0x2ull
> >  #define VMX_EPT_EXECUTABLE_MASK                      0x4ull
> >  #define VMX_EPT_IPAT_BIT                     (1ull << 6)
> > -#define VMX_EPT_ACCESS_BIT                   (1ull << 8)
> > +#define VMX_EPT_PSE_BIT                              (1ull << 7)
>
> I'm not a fan of "PSE", it's unnecessarily terse and "PSE" has different meaning
> in IA32 paging.  VMX_EPT_PAGE_SIZE_BIT would be choice.
>
> As for justification, something that has been mentioned once or thrice is the lack
> of build-time assertions that the PT_* bits in mmu.h that are reused for EPT entries
> do indeed match the EPT definitions.  I can throw together a patch/series to add
> that and do the below cleanup.
>
> > +#define VMX_EPT_ACCESS_SHIFT                 8
>
> I'd prefer we don't define the "shifts" for EPT (or PTE) bits, they really shouldn't
> be used as doing things like test_and_clear_bit() via a shift value can generate
> unnecessary lock instructions.  arch/x86/kvm/mmu.h could use a bit of spring cleaning
> in this regard.
>
> > +#define VMX_EPT_ACCESS_BIT                   (1ull << VMX_EPT_ACCESS_SHIFT)
> >  #define VMX_EPT_DIRTY_BIT                    (1ull << 9)
> >  #define VMX_EPT_RWX_MASK                        (VMX_EPT_READABLE_MASK |       \
> >                                                VMX_EPT_WRITABLE_MASK |       \
> > --
> > 2.35.0.rc0.227.g00780c9af4-goog
> >