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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 11 Nov 2025, at 8:06, David Hildenbrand (Red Hat) wrote: > On 11.11.25 04:25, Zi Yan wrote: >> On 10 Nov 2025, at 17:21, Lorenzo Stoakes wrote: >> >>> The kernel maintains leaf page table entries which contain either: >>> >>> - Nothing ('none' entries) >>> - Present entries (that is stuff the hardware can navigate without faul= t) >> >> This is not true for: >> >> 1. pXX_protnone(), where _PAGE_PROTNONE flag also means pXX_present() is >> true, but hardware would still trigger a fault. >> 2. pmd_present() where _PAGE_PSE also means a present PMD (see the comme= nt >> in pmd_present()). > > I'll note that pte_present/pmd_present etc is always about "soft-present"= . > > For example, if the hardware does not have a hw-managed access bit, doing= a pte_mkyoung() would also clear the hw-valid/hw-present bit because we ha= ve to catch any next access done by hardware. > > [fun fact: some hardware has an invalid bit instead of a valid/present bi= t :) IIRC s390x falls into that category] > > Similar things happen on ordinary PROT_NONE of course (independent of pte= _protnone). > > A better description might be "there is a page/pfn mapped here, but it mi= ght not be accessible by the CPU right now". > > We have device-exclusive/device-private nonswap (before this series) entr= ies that fall into the same category, unfortunately ("there is something ma= pped there that is not accessible by the CPU") I agree. I am fine with the categorization using pte_none(), pte_present(), and softleaf. It is =E2=80=9Chardware can navigate without fault=E2=80=9D t= hat causes confusion. Removing this comment would work for me, since people can look at the definition of pXX_present() for further clarification. Best Regards, Yan, Zi