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linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb 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3JCwezEkduPWic2UsBW6wfS4Kdt0S/EH4UgZkGu+YuB94VLl33KvV9VJXOhio/55VxXgA/lK7VPzbFzpZrsENxIF59UWO26FgfvEonazbfosC0hqzCyrgFkWbGa6d7asxKfyKhNIhCQuQpn6Rd/GRVVd2YkqxOHVSfT9jc+h7DaglYbThBB8p0e9NuHn/llnpe4ip69GWyOXf2t3eEBeDMol0l0+VSaEmhziWELFK4xUoHhGDkQia2vaRFdyvBT/7anYcDwTACbpDVOKWvmZV+CMYS1s3rrLIVhcVoAwerYzqCQHv7MJmFxr+zb7WxP4KW4evj0+56KG2Ocb20gZggenNA9HYWjY0I0fDAkKXuh8MBJoIj2UJQ48/jKWgIN8sIC72B/Q9cZgandQmj0l/2/dwVpeE5FLdo7xQ8wmEEyA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/25/26 11:53, Lorenzo Stoakes (ARM) wrote: > On Fri, Sep 25, 2026 at 12:28:49AM -0700, Suren Baghdasaryan wrote: >> On Thu, Sep 17, 2026 at 9:25 AM Lorenzo Stoakes (ARM) wrote: >>> >>> When a user requests an mmap_action be performed in mmap_prepare, this >>> involves populating the VMA range with data. >>> >>> However, if the VMA is mergeable, it might then mistakenly be merged with >>> another VMA without having populated the range. >>> >>> Every mmap action currently available sets VMA flags such that the VMA >>> cannot be merged. >>> >>> However, to ensure that no future mmap action falls foul of this, assert >>> that this is the case upon mmap_prepare validation. >>> >>> Signed-off-by: Lorenzo Stoakes (ARM) >> >> Reviewed-by: Suren Baghdasaryan > > Thanks! > >> >>> --- >>> mm/vma.c | 9 +++++++++ >>> 1 file changed, 9 insertions(+) >>> >>> diff --git a/mm/vma.c b/mm/vma.c >>> index d6ed10cefc8f..62f2ce1ad5a1 100644 >>> --- a/mm/vma.c >>> +++ b/mm/vma.c >>> @@ -2809,6 +2809,15 @@ static int mmap_validate(unsigned long prev_start, unsigned long prev_end, >>> int mmap_prepare_validate(const struct vm_area_desc *prev_desc, >>> const struct vm_area_desc *desc) >>> { >>> + /* >>> + * It is not valid to execute mmap actions for VMAs which can be merged, >>> + * as any such merge would leave portions of the mapping incorrectly >>> + * unmapped. >>> + */ >>> + if (vma_flags_can_merge(&desc->vma_flags) && >>> + WARN_ON_ONCE(desc->action.type != MMAP_NOTHING)) >> >> Any reason you chose this "if (A && WARN_ON_ONCE(B))" pattern instead >> of a simpler "if (WARN_ON_ONCE(A && B))"? Unless there are races >> between A and B updates, I think these would be equivalent, right? > > They are equivalent yes! > > So it's more of a style thing, as that reads less clearly to me: > > if (WARN_ON_ONCE(vma_flags_can_merge(&desc->vma_flags) && > desc->action.type != MMAP_NOTHING)) > > And this version highlights what is the broken thing here (action type set) a > little more clearly though obviously that's only if mergeable so arguable. > > I don't have a really strong opinion though I can change it if you prefer? Looks clearer to me like that Acked-by: David Hildenbrand (Arm) -- Cheers, David