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b=FrDg8s7vhYdjTv5G4yrao0SsCIYEHjftwZKQKVQTOCNQooQkUEijLSR0pt7xW+ss9 baud6F/09FvIiE6d9bL5GVO/ApYEjz9F8G2wnjh84LB9l4gix+y6bQaYXNWWkzQTso 8Mgpjsn85i1Tmheg/gvwQJQrs9Z/oWU2fGVNob3oj1du2bG0Tdz/xR+xnAje3K5NZS +BwHU0zkb+QINA+rNVTFn28PBiQC8rghVMqnWR10xES8fK3MqF/AQwofvrH8yiejln lkHeMuk/GdC0haSzwiBpkgDDE9TVQN9qfh4gVHwNf4DaA+22tWY190rC43RIQabpqi z6KJ+74E4TslQ== Message-ID: Date: Thu, 18 Jun 2026 11:43:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 02/12] mm/rmap: Add try_to_unmap_hugetlb_one To: Lance Yang , dev.jain@arm.com Cc: akpm@linux-foundation.org, ljs@kernel.org, chrisl@kernel.org, kasong@tencent.com, hughd@google.com, liam@infradead.org, riel@surriel.com, vbabka@kernel.org, harry@kernel.org, jannh@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, baolin.wang@linux.alibaba.com, pfalcato@suse.de, ryan.roberts@arm.com, anshuman.khandual@arm.com References: <20260618074449.24974-1-lance.yang@linux.dev> <0fe2a584-c633-4f82-8c47-d204e3b39a57@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EE5F240009 X-Stat-Signature: gpoxgns5ge8s1u937dmryqeumccf7fex X-Rspam-User: X-HE-Tag: 1781775800-637211 X-HE-Meta: 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 gmGgS5ea hWAQ8A8ghkDXlFT1MmaEvQhaC25D4jsTbIP7p01TwMN/jkoyErbXsDRYVkDiq9jA+3x7j9XSNxwpuZcFh15ULug7vsoHA+7B6EPxdYD2O+MOX/lFKQ9Wy2RLC3EoPiRQ6Q+kKeSBZ3kn3ypRC3SWTEmVRugvCVWfU4jCwaWOaYbK8J6hE0nzrlp2ZoGbI/anZxS8Xf2kPj4wZswvm9BPIbl/BcjgilenYWPLXBmJ2qU6q3ltHZAa95+9nXE6lR8YUw0ubb213hpqgn0Kns/d7zqyxBgJdstpTRVwNSJjnZG5sSerp8vC4oF/Vk7L0D7JurOtOg30alEYhwlo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/18/26 11:09, Lance Yang wrote: > > > On 2026/6/18 15:55, David Hildenbrand (Arm) wrote: >>>     return __rste_to_pte(pte_val(*ptep)); >>> } >>> >>> >>> So plain ptep_get() can feed raw huge-entry bits into pte_pfn(), and the >>> derived subpage can be wrong. >> >> Good question which impact that might have in practice? > > The subpage check can warn, but we still pass that subpage to > make_hwpoison_entry(). So the hwpoison marker can end up with the > wrong PFN? > > +    subpage = folio_page(folio, pte_pfn(pteval) - folio_pfn(folio)); > +    VM_WARN_ON(folio_page(folio, 0) != subpage); > [...] > +    pteval = swp_entry_to_pte(make_hwpoison_entry(subpage)); My s390x page table knowledge is a bit rusty. IIUC, it would be a problem if some PTE bits in segment/region entries (pmd/pud/ ...) would pass the pte_pfn(x) -> (pte_val(x) >> PAGE_SHIFT) check. I don't think this applies, because While #define _SEGMENT_ENTRY_ORIGIN_LARGE ~0xfffffUL We also have #define _SEGMENT_ENTRY_ORIGIN ~0x7ffUL So these bits are not actually used. What __rste_to_pte() primarily does is reshuffling present bits etc. So using any other bits besides the PFN would be problematic I guess. Am I wrong or isn't the present bit already at a different location? For prot-none hugetlb folios there might be a real issue, as the PTE present bit corresponds to the PMD/PUD read-permission bit. Oh my :) So yeah, we should probably fix that ahead of time unless I am missing something? Good that we separate that hugetlb crap out. -- Cheers, David