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linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev, Ihor Solodrai , Bert Karwatzki Subject: Re: [PATCH v5 24/38] mm/vma: enforce that mm-managed mappings may not set VMA_IO_BIT Message-ID: References: <20261009-b4-mmap-prepare-vma-flag-sanify-v5-0-923b70125b1e@kernel.org> <20261009-b4-mmap-prepare-vma-flag-sanify-v5-24-923b70125b1e@kernel.org> <5d51b6b3-ad58-4827-bedf-f1a79ebd5c86@kernel.org> <5ba7305f-0ad1-44ee-be0b-36752684cdb9@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5ba7305f-0ad1-44ee-be0b-36752684cdb9@kernel.org> X-Rspamd-Queue-Id: B6D0040003 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: cax8rexhano4j4f3hz8z4trpnr13uccj X-HE-Tag: 1791830961-885967 X-HE-Meta: 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Zyf/sybTEjGZksnYDcRHuyp973kulO4y9+5QiTNM6KNo+YNDjwfCzuMPbXq7Mkr8HwlcYzn2fX/tNC6Y/Yof/0ricDXeKtA5NvT6LKr8hzsn4puCVfyF3aWQdyJ4L109ONQQe/z8d3pwE3HH6zBHFaw89Xz4soCkxiPteLGM1HuF9IlOc4MbpYhKFzz+GPcIGZ26LJd67ZSWJOZjZVyCFI3DjHNBRyW68btrrQjjBJAn9ja9MWalWJtbtZ7sfFChBpM+0Fvedy4YoCas9RvTpIfF6U3fIjEan3xJfJ63zQ7xYIGdLYN88QEes/uba1ApfYQAlT0tOHkWA/m6Pl6QRRg/wl9vvoUHUCTOZhkQ166y3eugfmmTbiY1GN4naZvTSl2Swg+V61Bg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Oct 12, 2026 at 08:39:35PM +0200, David Hildenbrand (Arm) wrote: > On 10/12/26 20:35, Lorenzo Stoakes (ARM) wrote: > > On Mon, Oct 12, 2026 at 08:25:54PM +0200, David Hildenbrand (Arm) wrote: > >> On 10/9/26 20:04, Lorenzo Stoakes (ARM) wrote: > >>> It makes no sense for a mapping whose contents the kernel does not own to > >>> specify that the range is MMIO. > >>> > >>> Prior to this patch, all in-tree drivers which did so have been updated > >>> such that they are marked as not being mm-managed. The check WARNs and > >>> fails the mmap for any out-of-tree driver that still sets VMA_IO_BIT > >>> without a kernel mapping. > >>> > >>> No functional change intended for in-tree code. > >>> > >>> Reviewed-by: Zi Yan > >>> Signed-off-by: Lorenzo Stoakes (ARM) > >>> --- > >>> mm/vma.c | 6 ++++++ > >>> 1 file changed, 6 insertions(+) > >>> > >>> diff --git a/mm/vma.c b/mm/vma.c > >>> index 4f09fb98a2fd..51bdbe08bb02 100644 > >>> --- a/mm/vma.c > >>> +++ b/mm/vma.c > >>> @@ -2796,6 +2796,12 @@ static int mmap_validate_vma_flags(const vma_flags_t *flags) > >>> return -EINVAL; > >>> #endif > >>> > >>> + if (!vma_flags_test_any(flags, VMA_PFNMAP_BIT, VMA_MIXEDMAP_BIT)) { > >>> + /* mm-managed mappings may not set VMA_IO_BIT. */ > >>> + if (WARN_ON_ONCE(vma_flags_test(flags, VMA_IO_BIT))) > >>> + return -EINVAL; > >> > >> We do have a helper (vma_flags_is_mm_managed()) but we're not using it because > >> of the VM_IO situation ... > > > > That gets removed. > > > >> > >> That's confusing ... > >> > >> Could we do something like testing vma_flags_is_mm_managed(), but removing the > >> VM_IO flag from the checked flags? > > > > I mean we do that in a subsequent commit, I think even the next one? > > > > > >> > >> Then we can add a comment about VM_IO in the future getting remove from > >> vma_flags_is_mm_managed() ... > > > > Yeah, but to do that the code would now be something like: > > > > vma_flags_t masked = flags; > > > > /* > > * vma_flags_is_mm_managed() tests VMA_IO_BIT, which will be removed > > * in the next commit. > > */ > > vma_flags_clear(&flags, VMA_IO_BIT); > > if (!vma_flags_is_mm_managed(masked)) { > > ... > > } > > > > Is that really worth it? > > > > I don't think there's really too much confusion intra-patch about that is there? > > I would do it as above (- the comment, as that is the next patch indeed) and > only remove the vma_flags_clear() in the next patch. > > But in any case, you should spell out that this is only temporary in the patch > description :) And then there's a 'masked' variable that is unused? You need to have two vma_flags_t variables to be able both clear VMA_IO_BIT and use vma_flags_is_mm_managed(). So the change would have to be + vma_flags_t masked = *flags; + + vma_flags_clear(&flags, VMA_IO_BIT); + if (!vma_flags_is_mm_managed(&masked)) { + ... + } Then: - vma_flags_t masked = *flags; - - vma_flags_clear(&flags, VMA_IO_BIT); - if (!vma_flags_is_mm_managed(&masked)) { + if (!vma_flags_is_mm_managed(flags)) { ... } Which doesn't really seem worth it for somebody who is confused between two patches mid-series. But if you feel strongly I can make the change like that? -- Cheers, Lorenzo