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b=Hp5YLrKCuRwe3favx/ifQ0p0b6aYrjP4n19amuwxse5OmQguLmG0YyNj3EnDwckEH 9gSsvHLNMTyKsKOLr6E5wN0uXlhlukk7/c7an/eOOp5NWFdPwxmLSbUvY0uKBYXBTZ H72u0JBu6aQyLFRN7l5Ep3mhYeZVVKHcKFpMJJh3q4qEU2c4IdRSe22N5szVcld7Vx OTIoSM/6N4MRj2VSA/+zk74U8Vj3sjb6L/+7zb7Gi09a7wChNKpBHLKTdQyMEOassi QjMMp48JEp1KzyUZFDv5/0duWDZGMtj+N8vNh2sNh+HKUvR+TXZWP4YVmpz0v/C26w Re0sRKfsAFAsQ== Message-ID: <16fb7985-ec0f-4b56-91e7-404c5114f899@kernel.org> Date: Mon, 9 Feb 2026 10:55:32 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 4/5] arm64: mm: implement the architecture-specific clear_flush_young_ptes() To: Baolin Wang , Chris Mason Cc: akpm@linux-foundation.org, catalin.marinas@arm.com, will@kernel.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, riel@surriel.com, harry.yoo@oracle.com, jannh@google.com, willy@infradead.org, baohua@kernel.org, dev.jain@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <9d866a2644051e13a41ef4d6ca3909c6e1f9e229.1766631066.git.baolin.wang@linux.alibaba.com> <20260128114936.72280-1-clm@meta.com> <07d55759-a50a-457a-badd-85697174116f@kernel.org> <280ae63e-d66e-438f-8045-6c870420fe76@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: xw61ysxgmsbjim4fo1ewuio69d1rursr X-Rspamd-Queue-Id: 57A5BC0010 X-Rspam-User: X-HE-Tag: 1770630942-296504 X-HE-Meta: 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 pLKPBMSo 44FDzX+Lo4keQ3X0hfNixXhl77vkge4rBoxzOiUsK17q+fMGEGW3NvHmpINQmGwdpq7AC30ugFTe/JHNTwHB1Kkqac+cEzZvu6Ygau4TToD2vQlURuSMEr8umRQ8dfQoAS5Bzdnui2wMTpd5Z3VC2zcMPWFMlXqcYSVwySJyjJEoxqvRbAJWaGZdtFuQwCan5cjE2+UKcs6QXRbCX5AzoBx6Apk0JoL9qsp0HvpZIYNMNqaSupovxgxoGFKTCPx+y4ORXLON7dfXgBMvmCr888b27vdtdiY6hDuoWhmbeRCWc/eiapVgjXgGqc5N74E+wv/uh7AwgLu0NxW8= 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 2/9/26 10:36, Baolin Wang wrote: > > > On 2/9/26 5:09 PM, David Hildenbrand (Arm) wrote: >> On 1/29/26 02:42, Baolin Wang wrote: >>> >>> >>> >>> Indeed. I previously discussed with Ryan whether using pte_cont() was >>> enough, and we believed that invalid PTEs wouldn’t have the PTE_CONT >>> bit set. But we clearly missed the device-folio cases. Thanks for >>> reporting. >>> >>> Andrew, could you please squash the following fix into this patch? If >>> you prefer a new version, please let me know. Thanks. >> >> Isn't the real problem that we should never ever ever ever, try >> clearing the young bit on a non-present pte? >> >> See damon_ptep_mkold() how that is handled with the flushing/notify. >> >> There needs to be a pte_present() check in the caller. > > The handling of ZONE_DEVICE memory in check_pte() makes me me doubt my > earlier understanding. And I think you are right. > >     } else if (pte_present(ptent)) { >         pfn = pte_pfn(ptent); >     } else { >         const softleaf_t entry = softleaf_from_pte(ptent); > >         /* Handle un-addressable ZONE_DEVICE memory */ >         if (!softleaf_is_device_private(entry) && >             !softleaf_is_device_exclusive(entry)) >             return false; > >         pfn = softleaf_to_pfn(entry); >     } > > >> BUT >> >> I recall that folio_referenced() should never apply to ZONE_DEVICE >> folios. folio_referenced() is only called from memory reclaim code, >> and ZONE_DEVICE pages never get reclaimed through vmscan.c > > Thanks for clarifying. So I can drop the pte valid check. We should probably add a safety check in folio_referenced(), warning if we would ever get a ZONE_DEVICE folio passed. Can someone look into that ? :) -- Cheers, David