Re: [PATCH v6 13/41] mm: Make pte_mkwrite() take a VMA

From: Michael Ellerman <mpe@ellerman.id.au>
To: Rick Edgecombe <rick.p.edgecombe@intel.com>,
	x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
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	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
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	Florian Weimer <fweimer@redhat.com>,
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Cc: rick.p.edgecombe@intel.com, linux-alpha@vger.kernel.org,
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Subject: Re: [PATCH v6 13/41] mm: Make pte_mkwrite() take a VMA
Date: Mon, 20 Feb 2023 12:00:46 +1100	[thread overview]
Message-ID: <875ybxywu9.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20230218211433.26859-14-rick.p.edgecombe@intel.com>

Rick Edgecombe <rick.p.edgecombe@intel.com> writes:
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
...
> ---
> Hi Non-x86 Arch’s,
>
> x86 has a feature that allows for the creation of a special type of
> writable memory (shadow stack) that is only writable in limited specific
> ways. Previously, changes were proposed to core MM code to teach it to
> decide when to create normally writable memory or the special shadow stack
> writable memory, but David Hildenbrand suggested[0] to change
> pXX_mkwrite() to take a VMA, so awareness of shadow stack memory can be
> moved into x86 code.
>
> Since pXX_mkwrite() is defined in every arch, it requires some tree-wide
> changes. So that is why you are seeing some patches out of a big x86
> series pop up in your arch mailing list. There is no functional change.
> After this refactor, the shadow stack series goes on to use the arch
> helpers to push shadow stack memory details inside arch/x86.
...
> ---
>  Documentation/mm/arch_pgtable_helpers.rst    |  9 ++++++---
>  arch/alpha/include/asm/pgtable.h             |  6 +++++-
>  arch/arc/include/asm/hugepage.h              |  2 +-
>  arch/arc/include/asm/pgtable-bits-arcv2.h    |  7 ++++++-
>  arch/arm/include/asm/pgtable-3level.h        |  7 ++++++-
>  arch/arm/include/asm/pgtable.h               |  2 +-
>  arch/arm64/include/asm/pgtable.h             |  4 ++--
>  arch/csky/include/asm/pgtable.h              |  2 +-
>  arch/hexagon/include/asm/pgtable.h           |  2 +-
>  arch/ia64/include/asm/pgtable.h              |  2 +-
>  arch/loongarch/include/asm/pgtable.h         |  4 ++--
>  arch/m68k/include/asm/mcf_pgtable.h          |  2 +-
>  arch/m68k/include/asm/motorola_pgtable.h     |  6 +++++-
>  arch/m68k/include/asm/sun3_pgtable.h         |  6 +++++-
>  arch/microblaze/include/asm/pgtable.h        |  2 +-
>  arch/mips/include/asm/pgtable.h              |  6 +++---
>  arch/nios2/include/asm/pgtable.h             |  2 +-
>  arch/openrisc/include/asm/pgtable.h          |  2 +-
>  arch/parisc/include/asm/pgtable.h            |  6 +++++-
>  arch/powerpc/include/asm/book3s/32/pgtable.h |  2 +-
>  arch/powerpc/include/asm/book3s/64/pgtable.h |  4 ++--
>  arch/powerpc/include/asm/nohash/32/pgtable.h |  2 +-
>  arch/powerpc/include/asm/nohash/32/pte-8xx.h |  2 +-
>  arch/powerpc/include/asm/nohash/64/pgtable.h |  2 +-

Looks like you discovered the joys of ppc's at-least 5 different MMU
implementations, sorry :)

Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)

cheers

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