linux-kernel - Re: [PATCH v2 10/39] x86/mm: Introduce _PAGE

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Message-ID: <43fa92845d9883655dd20c49977ca399671bde20.camel@intel.com>
Date:   Thu, 6 Oct 2022 16:10:43 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "jannh@...gle.com" <jannh@...gle.com>
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Subject: Re: [PATCH v2 10/39] x86/mm: Introduce _PAGE_COW

On Fri, 2022-09-30 at 17:16 +0200, Jann Horn wrote:
> On Fri, Sep 30, 2022 at 12:30 AM Rick Edgecombe
> <rick.p.edgecombe@...el.com> wrote:
> > The reason it's lightly used is that Dirty=1 is normally set
> > _before_ a
> > write. A write with a Write=0 PTE would typically only generate a
> > fault,
> > not set Dirty=1. Hardware can (rarely) both set Write=1 *and*
> > generate the
> > fault, resulting in a Dirty=0,Write=1 PTE. Hardware which supports
> > shadow
> > stacks will no longer exhibit this oddity.
> 
> Stupid question, since I just recently learned that IOMMUv2 is a
> thing: I assume this also holds for IOMMUs that implement
> IOMMUv2/SVA,
> where the IOMMU directly walks the userspace page tables, and not
> just
> for the CPU core?

Sorry for the delay, I had to go find out. IOMMU behaves similar to the
CET CPUs in this regard. Thanks for the question.