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charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 6/27/26 04:46, Li,Rongqing wrote: >> >> >> >> On 6/25/26 4:39 AM, lirongqing wrote: >>> From: Li RongQing >>> >>> split_contpmd() modifies the pmd entries in-place by clearing the CONT >>> bit, but the local 'pmd' variable still holds the old snapshot with >>> CONT set. The subsequent split_pmd() call uses this stale value to >>> derive the pgprot for the new PTE entries via pmd_pgprot(), causing >>> the resulting PTEs to be populated with incorrect protection bits. >> >> If I read the code correctly, CONT bit is cleared by split_pmd(), then the bit >> may be set again for PTEs if we want to have cont ptes. So I don't see any >> problem, did I miss something? >> > > You are right, there's no functional issue with the current code. > However, I think explicitly re-reading the pmd is the safer and clearer > approach — it makes the intent obvious (we need the post-modification state) > rather than relying on the implicit assumption that "CONT bit doesn't affect pgprot." Note that it's going to be another read (READ_ONCE()) that cannot be optimized out. Manual pmd_mknoncont() might be cheaper. But then, nobody care about it being set or not ... -- Cheers, David