Re: [PATCH v5 24/38] mm/vma: enforce that mm-managed mappings may not set VMA_IO_BIT
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From: "David Hildenbrand (Arm)" <david@kernel.org>
Date: 2026-10-12 18:26:29
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bpf, dri-devel, fuse-devel, kvm, kvm-riscv, kvmarm, linux-arch, linux-doc, linux-fsdevel, linux-mm, linux-perf-users, linux-rdma, linux-riscv, linux-s390, linux-scsi, linux-sound, linux-trace-kernel, linux-usb, linuxppc-dev, lkml, selinux, sparclinux
On 10/9/26 20:04, Lorenzo Stoakes (ARM) wrote:
quoted hunk ↗ jump to hunk
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 <ziy@nvidia.com> Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> --- 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's confusing ... Could we do something like testing vma_flags_is_mm_managed(), but removing the VM_IO flag from the checked flags? Then we can add a comment about VM_IO in the future getting remove from vma_flags_is_mm_managed() ... -- Cheers, David