Re: [RESUBMIT][PATCH] x86/mm: Fix PAT bit missing from page protection modify mask

[Borislav Petkov]

On Thu, Jun 01, 2023 at 10:47:39AM +0200, Juergen Gross wrote:
> As described in the commit message, this only works on bare metal due to the
> PAT bit not being needed for WC mappings.
>
> Making this patch Xen specific would try to cure the symptoms without fixing
> the underlying problem: _PAGE_PAT should be regarded the same way as the bits
> for caching mode (_PAGE_CHG_MASK).

So why isn't _PAGE_PAT part of _PAGE_CHG_MASK?

It says above it "Set of bits not changed in pte_modify."

And I don't see pte_modify() changing that bit either.

Right now this "fix" looks like, "let's OR these two masks so that we
can take care of _PAGE_PAT too". But it doesn't make a whole lotta sense
to me...

-- 
Regards/Gruss,
    Boris.

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