From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4ECAB315D29 for ; Thu, 18 Jun 2026 09:43:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781775801; cv=none; b=YXoclkC3rUEBXGEjv+Datyh4zhDtoqzcgZ8G/fDjDGZS81fOxu9yoPF5knXOe7MM/fIs6gU0b3NuWDbZN/tA6qZ0hUV67VYOuXmwIQ8fGCK8Cqp3+YnptpEWQ87cwPmbJ8sqbFkB3HUjqT8QLZkO2w40Pzz9u3udqYwlZRCtjTY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781775801; c=relaxed/simple; bh=hY+UIucKZuyR1OuQKb2K1ghf1obr4X7tWsK8rqbWtDA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lvmdJzljaw3B01krfetCmqpLgGve62fgpTATHogLq6TTzrQg6PrAhJ9iEPP4rkxqcQ5W8N7hsIcifVjtK7E2YfC6M7nv4nYCfdHWuf1ZTsPsO3ttsPNVrwcSTtrfODVczNNYJrv5p2+/ddUn2OkLgg7nd3XzBu6YfUmLcR5T1EM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FrDg8s7v; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="FrDg8s7v" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0DB9B1F000E9; Thu, 18 Jun 2026 09:43:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781775799; bh=LZ+WWK/EtN/+c7t/LuN/tcS76BgfUhzIxVF7vA6SHLk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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