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Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato Subject: Re: [RFC PATCH 2/6] mm: nommu: use vma_is_anonymous() to check if vmas are anonymous Message-ID: References: <20260813063401.1786548-1-thehajime@gmail.com> <20260813063401.1786548-3-thehajime@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260813063401.1786548-3-thehajime@gmail.com> X-Rspam-User: X-Stat-Signature: qrsdafop6tt3d8h3ttskyrmybnc1hsj3 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: D0A15140003 X-HE-Tag: 1786708380-233201 X-HE-Meta: U2FsdGVkX1/zgUlB1BBxtnu9PHNg0Dn0W2mr4BZq37XZ5JX09KCgrJbrg/z9Um5AWC4oc5M9EdPp6m9KRRIp1bo7ou363diUwYnrauP67mFFmOxD0IX+5fOYVdZfEW6irw57dWlYgYudf3uDjCkzRi9uBPOSIo/gNqXAl3H9pUkHJX7g4ltx3SCDhTGaFNbn8d51qamyKzp0Z2yw+3JzvMWC26Bp9dQ6MxCui7Le76LjcCwWJRz4uAympOmqnUsyZrWdCdioxbn5q5Ah5HhXCs7QSkWlrKhYzCRuVT2hJDWAhUsa/Hh5yR7LZFZ73Hw/o3y4oq5YD7ZQ08wm+9pc/UYd+K3xYQOdZaeV17l6vfHyfAq84o4T247XPiJZLjqy8nAknrHXVZXn9GuihYbU58x6IhDzXh8qpsyPx4lpaUyBsATFpHYEqDytvM2YcnroiGV1glHwjoQZBCIIgVeH0z4+z/RofiCFa94RdwMKBezWk9TJqISl+EHlvHFE8CnD8+fBhiH+UXosFmTpmeaGNSU9g9MSzB7UGOUE14R+/NEfHci/cPGiVTlitcKRDw42yIRmFVFywFARzNfGs7T8K+CHABNgPAvemm5q8GDI6UHcZPtxyrkXO+6a1NnIpfscnhOIsDI6qRx4mdnJnyPrdqzy8uI04gHpS7lZQb3bPSB3j16694Ktf0jZW8JOiGV+Prlq3D55LBeX94PWFh4KESqwjnn0a2A8HYU7ll2NFa8rsIyYwhtXGP+sYqFxera+dgtCwa76omAWhdi0esWwBkioNWQr+oXpifwV/VRZX3gLtXrSrrl1Fp9+0a7ww7iCn16yQzdRuW0R+7ULDsZGmK1WcRMBli8IVnKj3IaVgZak76OCN8aX9FrgQt+ZhCIA0QjSJU28ipIA6Zot4MSHplyKV2FRsCJchBXrA3VaezV+G2Z5Jh6KIXvnNq4ChMG7KIyerX9vxGE12pHw3Wq AAoZZykT 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 13, 2026 at 03:33:57PM +0900, Hajime Tazaki wrote: > Private file mappings (like those from /dev/zero) can have vma->vm_file > set but remain structurally anonymous since they lack vm_ops. Testing > vma->vm_file instead of vma_is_anonymous(vma) might cause mremap to > return a spurious -EINVAL when userspace attempts to shrink these > mappings. > > This commit fixes this issue by using vma_is_anonymous() instead of > testing vma->vm_file to address the case of /dev/zero. > > Cc: Andrew Morton > Cc: "Liam R. Howlett" > Cc: Lorenzo Stoakes > Cc: Vlastimil Babka > Cc: Jann Horn > Cc: Pedro Falcato > Cc: linux-mm@kvack.org > Closes: https://sashiko.dev/#/patchset/20260710054648.924005-1-thehajime%40gmail.com > Signed-off-by: Hajime Tazaki As staged in review on 1/6 you need to squash this somehow. > --- > mm/nommu.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/nommu.c b/mm/nommu.c > index 89444ee2aca6..e40990e15831 100644 > --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -1196,7 +1196,7 @@ unsigned long do_mmap(struct file *file, > add_nommu_region(region); > > /* clear anonymous mappings that don't ask for uninitialized data */ > - if (!vma->vm_file && > + if (vma_is_anonymous(vma) && > (!IS_ENABLED(CONFIG_MMAP_ALLOW_UNINITIALIZED) || > !(flags & MAP_UNINITIALIZED))) > memset((void *)region->vm_start, 0, > @@ -1328,7 +1328,7 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, > > /* we're only permitted to split anonymous regions (these should have > * only a single usage on the region) */ > - if (vma->vm_file) > + if (!vma_is_anonymous(vma)) > return -ENOMEM; > > mm = vma->vm_mm; > @@ -1484,7 +1484,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len, struct list > } > > /* we're allowed to split an anonymous VMA but not a file-backed one */ > - if (vma->vm_file) { > + if (!vma_is_anonymous(vma)) { > do { > if (start > vma->vm_start) > return -EINVAL; > @@ -1617,7 +1617,7 @@ static unsigned long do_mremap(unsigned long addr, > /* like do_munmap(), we're allowed to shrink an anonymous VMA but not > * a file-backed one > */ > - if (vma->vm_file) > + if (!vma_is_anonymous(vma)) > return (unsigned long) -EINVAL; > > /* vmi_shrink_vma() needs from/to pointers to be removed, > -- > 2.43.0 > -- Cheers, Lorenzo