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Date:   Tue, 13 Jun 2023 14:28:13 +0200
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Subject: Re: [PATCH v9 03/42] mm: Make pte_mkwrite() take a VMA
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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>, linux-kernel@vger.kernel.org,
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        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H . J . Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
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        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Weijiang Yang <weijiang.yang@intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        John Allen <john.allen@amd.com>, kcc@google.com,
        eranian@google.com, rppt@kernel.org, jamorris@linux.microsoft.com,
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        Andrew.Cooper3@citrix.com, christina.schimpe@intel.com,
        debug@rivosinc.com, szabolcs.nagy@arm.com,
        torvalds@linux-foundation.org, broonie@kernel.org
References: <20230613001108.3040476-1-rick.p.edgecombe@intel.com>
 <20230613001108.3040476-4-rick.p.edgecombe@intel.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <20230613001108.3040476-4-rick.p.edgecombe@intel.com>
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On 13.06.23 02:10, Rick Edgecombe wrote:
> The x86 Shadow stack 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.
> 
> One of these unusual properties is that shadow stack memory is writable,
> but only in limited ways. These limits are applied via a specific PTE
> bit combination. Nevertheless, the memory is writable, and core mm code
> will need to apply the writable permissions in the typical paths that
> call pte_mkwrite(). Future patches will make pte_mkwrite() take a VMA, so
> that the x86 implementation of it can know whether to create regular
> writable memory or shadow stack memory.
> 
> But there are a couple of challenges to this. Modifying the signatures of
> each arch pte_mkwrite() implementation would be error prone because some
> are generated with macros and would need to be re-implemented. Also, some
> pte_mkwrite() callers operate on kernel memory without a VMA.
> 
> So this can be done in a three step process. First pte_mkwrite() can be
> renamed to pte_mkwrite_novma() in each arch, with a generic pte_mkwrite()
> added that just calls pte_mkwrite_novma(). Next callers without a VMA can
> be moved to pte_mkwrite_novma(). And lastly, pte_mkwrite() and all callers
> can be changed to take/pass a VMA.
> 
> In a previous patches, pte_mkwrite() was renamed pte_mkwrite_novma() and
> callers that don't have a VMA were changed to use pte_mkwrite_novma(). So
> now change pte_mkwrite() to take a VMA and change the remaining callers to
> pass a VMA. Apply the same changes for pmd_mkwrite().
> 
> No functional change.
> 
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

Hopefully we'll get this landed soon :)

-- 
Cheers,

David / dhildenb