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b=mQIS2QV1bPwjZk0hf8iL5T1QRYtqruXH8dUTmESiRvvZFkgk1bY3YPXdULUbPjGi/ o6uLXrjU1xnKp8U630fiEHJZimm+hFOIXFfdj2Ahf5plOsLCuQGutIxR20QXO2zQoi 9j8/rQM8IkAYoRL0fpumj5VBxqa+ihnC9XoBLhWIpk/riTQT9ZNn9QVF8NZGPLZlnl Ihmjya9O7FNRYUGNbqf20PCo/+VCMG6b13/+x2xC9W4sEQIlFtaE+qxaVyruLh6h93 cbCv/H95k5JissU3vM4hrBlTz5Qx7lVpC1RPhV6QkuTFRVsglrerUFDkhzZ1MpRu8v MI+IAc7Rzs0ww== Message-ID: Date: Tue, 4 Aug 2026 20:34:43 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Fix incorrect flush address in direct page table reclaim From: "David Hildenbrand (Arm)" To: Qi Zheng , luto@kernel.org, linux-mm@kvack.org Cc: luto@amacapital.net, Liam Howlett , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Andrew Morton , stable@vger.kernel.org References: <20260804003708.49830-1-luto@kernel.org> <313133db-3b94-4a63-8bcd-21952ff77e41@kernel.org> <8cf8eaca-fc04-4a68-bbc8-50ecdbf96382@linux.dev> <3d3aa670-76bc-4df3-9c36-609c14354e9e@kernel.org> Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: DE181120004 X-Stat-Signature: 1yhsacao9mae69z19pfreq57whw8uz96 X-Rspam-User: X-HE-Tag: 1785868491-723821 X-HE-Meta: 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 qeo5BSi1 /xAXPFeQ31E3ri29KewGHIijIHTCxx8pkuhzImYJaLxoAcwJnF+IziZL4SMi5wzzacm0ZVBv751djg4FpiV8igAOcQFKrwH9HplkttMIHrXEmusqDLJnvQKfu669C72JqQu0l03caN1RkWuEreImdoxmTXsnHDvHeC0+hRARgAQaEGPSc74dyUqr2OnrioFAkUegVnVh8shNOVcer/Mo3XmDAClxso/IUQAPfmdMv4GSjpoQVXteoWUy1pBdpJMLK19Fm Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/4/26 11:34, David Hildenbrand (Arm) wrote: > On 8/4/26 11:25, Qi Zheng wrote: >> >> >> On 8/4/26 5:05 PM, David Hildenbrand (Arm) wrote: >>> >>> Note that this only triggers when someone does e.g., a MADV_DONTNEED over >>> a large enough range (covering at least a full PTE table). >>> >>> So this isn't the ordinary munmap()/exit() page table reclaim code. >>> >>> I'm still surprised that it took so long to show up; likely we need more >>> targeted tests for PT_RECLAIM that >> >> We backported the PT_RECLAIM to our internal tree a while ago (excluding >> the rework patch being fixed here), and it has been running stably ever >> since. > > I'm wondering whether we should have a selftest that triggers this exact scenario: > > (a) Populate page table(s) > (b) MADV_DONTNEED to reclaim the page table(s) > (c) Allocate plenty of pages for another purpose (draining PCP where the page > table likely ended up) and fill them with some data that looks like present page > table entries. > (d) Re-access the reclaimed VA space, expecting re-population of anonymous > pages. FWIW, I tried to reproduce above and on x86 it's really not able to trigger easily (as you say, might require some prefetching tricks). I was able to trigger "something" on arm64, which is just an endless loop between HW saying "translation exception" and the MM logic saying "looks good me, continue". As soon as the walk cache gets flushed (due to some concurrent activity in the system), the reproducer continues. -- Cheers, David