linux-kernel - Re: [PATCH hotfix 6.12 v3 4/5] mm: refactor arch_validate

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Message-ID: <00a06ba2-e9ad-46a8-a3f3-5d4ad9eb1c00@lucifer.local>
Date: Tue, 29 Oct 2024 16:21:22 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Yang Shi <shy828301@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>
Subject: Re: [PATCH hotfix 6.12 v3 4/5] mm: refactor arch_validate_flags()
 and arm64 MTE handling

On Tue, Oct 29, 2024 at 09:08:22AM -0700, Yang Shi wrote:
> On Tue, Oct 29, 2024 at 8:52 AM Lorenzo Stoakes
> <lorenzo.stoakes@...cle.com> wrote:
> >
> > On Tue, Oct 29, 2024 at 08:43:04AM -0700, Yang Shi wrote:
> >
> > >
> > > Sorry for chiming in late. This looks problematic IIUC. The patch 5/5
> > > moved arch_validate_flags() before call_mmap() as the commit log said.
> > > But shmem_file() does this check:
> > > mapping->a_ops == &shmem_aops
> > >
> > > But mapping->a_ops is not initialized until shmem_mmap(), which is
> > > called by call_mmap().
> > >
> > > So shmem_file() should always return false here. Did I miss something?
> >
> > Well firstly this is tested and works so you did miss something :)
> >
> > Bu shmem_mmap() is not setting mapping->a_ops, it's setting vma->vm_ops.
> >
> > __shmem_get_inode() and shmem_symlink() set mapping->a_ops.
>
> My bad, stared at "_ops", but missed "vm" prefix. And shmem_mmap()
> can't touch a_ops. Sorry for the disruption.

No worries, the various ops are quite confusing and precisely where what
happens, I had to double check this myself... :)