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Howlett" , Vlastimil Babka , Jann Horn , Pedro Falcato , Jeff Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org, antonius Subject: Re: [PATCH mm-hotfixes] mm/mseal: update VMA end correctly on merge Message-ID: <5739bab8-d75f-404d-a3c8-a67f91e072a5@lucifer.local> References: <20260327090640.146308-1-ljs@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 9CB20140003 X-Stat-Signature: wxxow6kx9akwoc87ohp36imn6eyu4mpq X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1774632220-373924 X-HE-Meta: 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 OH1VAMKI hNn9y0ZAuV2v1jUIXuSSTzRrp9uUY/0SGmVIg7pjhc612VHvPxQNaa69PC7Uh0/6ty1FI5XxGB6hMJGCeMVf8rFIvO/2nEOjCPDzqiseVzNBAJw8sGoJBshwJo/0S6xKY+q5Qb5Lg8Sig28U0Gxu+dEZU6i+Am7UXfgNTskpe/BPGZmQtvJdka8KaSHNP4A//ArCuC8vu+Z2ZkW2yAWeOuyKuzrYI2A8YlPu6Z2ggPiA8h6/ooChpz82WTlIDhIxQjtAlv7/SKmt9TPUa1godlJOTSwlJN+uB4OT0dCj95mxe8QFACUT9ZmtKbpgE6nxvCCZh Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Mar 27, 2026 at 05:57:06PM +0100, David Hildenbrand (Arm) wrote: > On 3/27/26 10:06, Lorenzo Stoakes (Oracle) wrote: > > Previously we stored the end of the current VMA in curr_end, and then upon > > iterating to the next VMA updated curr_start to curr_end to advance to the > > next VMA. > > > > However, this doesn't take into account the fact that a VMA might be > > updated due to a merge by vma_modify_flags(), which can result in curr_end > > being stale and thus, upon setting curr_start to curr_end, ending up with > > an incorrect curr_start on the next iteration. > > > > Resolve the issue by setting curr_end to vma->vm_end unconditionally to > > ensure this value remains updated should this occur. > > > > Signed-off-by: Lorenzo Stoakes (Oracle) > > Fixes: 6c2da14ae1e0 ("mm/mseal: rework mseal apply logic") > > Cc: > > Reported-by: Antonius > > Closes: https://lore.kernel.org/linux-mm/CAK8a0jyHXqBpt8Xe8v9SNDbnRiwz7OthA8SKY=NLRY7smPEP3Q@mail.gmail.com/ > > --- > > mm/mseal.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/mm/mseal.c b/mm/mseal.c > > index 316b5e1dec78..2d72a15d8ea1 100644 > > --- a/mm/mseal.c > > +++ b/mm/mseal.c > > @@ -66,7 +66,7 @@ static int mseal_apply(struct mm_struct *mm, > > prev = vma; > > > > for_each_vma_range(vmi, vma, end) { > > - const unsigned long curr_end = MIN(vma->vm_end, end); > > + unsigned long curr_end = MIN(vma->vm_end, end); > > > > if (!(vma->vm_flags & VM_SEALED)) { > > vm_flags_t vm_flags = vma->vm_flags | VM_SEALED; > > @@ -76,6 +76,7 @@ static int mseal_apply(struct mm_struct *mm, > > if (IS_ERR(vma)) > > return PTR_ERR(vma); > > vm_flags_set(vma, VM_SEALED); > > + curr_end = vma->vm_end; /* Merge may have updated. */ > > } > > > I was a bit confused why curr_start is allowed to not start within the VMA, > but before it. Then I recalled that range_contains_unmapped() checks for no holes. > > > Would the following also sort out the problem and even simplify the code? > > diff --git a/mm/mseal.c b/mm/mseal.c > index 603df53ad267..e2093ae3d25c 100644 > --- a/mm/mseal.c > +++ b/mm/mseal.c > @@ -56,7 +56,6 @@ static int mseal_apply(struct mm_struct *mm, > unsigned long start, unsigned long end) > { > struct vm_area_struct *vma, *prev; > - unsigned long curr_start = start; > VMA_ITERATOR(vmi, mm, start); > > /* We know there are no gaps so this will be non-NULL. */ > @@ -66,6 +65,7 @@ static int mseal_apply(struct mm_struct *mm, > prev = vma; > > for_each_vma_range(vmi, vma, end) { > + const unsigned long curr_start = MAX(vma->vm_start, start); Yeah that's nice :) > const unsigned long curr_end = MIN(vma->vm_end, end); > > if (!vma_test(vma, VMA_SEALED_BIT)) { > @@ -82,7 +82,6 @@ static int mseal_apply(struct mm_struct *mm, > } > > prev = vma; > - curr_start = curr_end; > } > > return 0; > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > I might be wrong about that, I've been staring at the screen for too long today. No this is better, I've mulled this over, this is much better :) Sorry to be a pain Andrew - let me respin this right now. I will retain tags as this is functionally equivalent, I have checked it locally, confirmed repro solved, checked against AI review also. > > > -- > Cheers, > > David Cheers, Lorenzo