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charset=us-ascii Content-Disposition: inline In-Reply-To: <791e0d59-0eb2-481f-bf8b-ba4b413d5ebd@redhat.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 273E810000F X-Stat-Signature: beb9dmatxgjgsk7sf4aq7xfdyd79y7or X-Rspam-User: X-HE-Tag: 1758708146-684865 X-HE-Meta: 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 taJPiN1F 1RJji1WdFNpYwa4JqG6WxrTy5LB9inr6VpFL+l5TyNmUIXwwF74uZCp+Ru7zk6GKX+uBJ/GE4al4fSMnOTRd2R55ktB3kaJ17nu9U9WApqhjINjfKbrR1JbqEEJY2BHc7drkGzEyKxWjE8x0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 24, 2025 at 11:44:19AM +0200, David Hildenbrand wrote: > On 24.09.25 11:34, Catalin Marinas wrote: > > On Wed, Sep 24, 2025 at 11:13:18AM +0200, David Hildenbrand wrote: > > > On 24.09.25 10:50, Catalin Marinas wrote: > > > > On Wed, Sep 24, 2025 at 10:49:27AM +0800, Lance Yang wrote: > > > > > On 2025/9/24 00:14, Catalin Marinas wrote: > > > > > > So alternative patch that also fixes the deferred struct page init (on > > > > > > the assumptions that the zero page is always mapped as pte_special(): > > > > > > > > > > I can confirm that this alternative patch also works correctly; my tests > > > > > for MTE all pass ;) > > > > > > > > Thanks Lance for testing. I'll post one of the variants today. > > > > > > > > > This looks like a better fix since it solves the boot hang issue too. > > > > > > > > In principle, yes, until I tracked down why I changed it in the first > > > > place - 68d54ceeec0e ("arm64: mte: Allow PTRACE_PEEKMTETAGS access to > > > > the zero page"). ptrace() can read tags from PROT_MTE mappings and we > > > > want to allow reading zeroes as well if the page points to the zero > > > > page. Not flagging the page as PG_mte_tagged caused issues. > > > > > > > > I can change the logic in the ptrace() code, I just need to figure out > > > > what happens to the huge zero page. Ideally we should treat both in the > > > > same way but, AFAICT, we don't use pmd_mkspecial() on the huge zero > > > > page, so it gets flagged with PG_mte_tagged. > > > > > > I changed that recently :) The huge zero folio will now always have > > > pmd_special() set. > > > > Oh, which commit was this? It means that we can end up with > > uninitialised tags if we have a PROT_MTE huge zero page since > > set_pmd_at/set_pte_at() skips mte_sync_tags(). > > This one: > > commit d82d09e482199e6bbc204df10b2082f764cbe1f4 > Author: David Hildenbrand > Date: Mon Aug 11 13:26:25 2025 +0200 > > mm/huge_memory: mark PMD mappings of the huge zero folio special > > The huge zero folio is refcounted (+mapcounted -- is that a word?) > differently than "normal" folios, similarly (but different) to the > ordinary shared zeropage. > > > It should be in mm-stable, to go upstream in the upcoming merge window. It's > been lurking in -next for a while now. Thanks. At least it's something to address in the next kernel version. I need to improve the MTE kselftests to catch the zero page scenarios. > As it behaves just like the ordinary shared zeropage now, would we have to > zero/initialize the tags after allocating it? Yes. Before pmd_special(), it was be done lazily via set_pmd_at(). I think it just needs a __GFP_ZEROTAGS. The only other place we use this flag is in vma_alloc_zeroed_movable_folio(), as an optimisation to avoid a separate loop for zeroing the tags after data. -- Catalin