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Fri, 20 Jun 2025 13:27:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id pBhfDL9hVWiXOQAAD6G6ig (envelope-from ); Fri, 20 Jun 2025 13:27:27 +0000 Date: Fri, 20 Jun 2025 15:27:25 +0200 From: Oscar Salvador To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, Andrew Morton , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Dan Williams , Alistair Popple , Matthew Wilcox , Jan Kara , Alexander Viro , Christian Brauner , Zi Yan , Baolin Wang , Lorenzo Stoakes , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato Subject: Re: [PATCH RFC 03/14] mm: compare pfns only if the entry is present when inserting pfns/pages Message-ID: References: <20250617154345.2494405-1-david@redhat.com> <20250617154345.2494405-4-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250617154345.2494405-4-david@redhat.com> X-Rspamd-Action: no action X-Stat-Signature: gm6wtt8i7d789t7cirxr9u644pz5qeia X-Rspamd-Queue-Id: 8E81180004 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1750426050-504727 X-HE-Meta: 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 3KzRakHZ RNSoncwPq89ZxEttyR/C2i+Fc9qI0U/nLo3b8FSgTR1CCK5dbqhQ2ogD5ujIqdS37taCeViWxOlqLwA1yIUrw/cbFo/b8WEFtTYn3jIFbmMMk+CqmT4ADQ47KxRitH9NT5md/X01qvP8/cBVlJhMUas799W91MlrSXA4h2ghHHzHyk/xE8120n6dh2CqdRL21E1U12aPJJ4HIn3jwpoOhexGqwm2eUA/mxOUVbRfJTiU1jO/41PmOZ+3jRuNYqTylnUcAtlMF/ltHbSKevde8Rog2IdF86itX7oj3 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 Tue, Jun 17, 2025 at 05:43:34PM +0200, David Hildenbrand wrote: > Doing a pte_pfn() etc. of something that is not a present page table > entry is wrong. Let's check in all relevant cases where we want to > upgrade write permissions when inserting pfns/pages whether the entry > is actually present. Maybe I would add that's because the pte can have other info like marker, swp_entry etc. > It's not expected to have caused real harm in practice, so this is more a > cleanup than a fix for something that would likely trigger in some > weird circumstances. > > At some point, we should likely unify the two pte handling paths, > similar to how we did it for pmds/puds. > > Signed-off-by: David Hildenbrand Reviewed-by: Oscar Salvador Should we scream if someone passes us a non-present entry? > --- > mm/huge_memory.c | 4 ++-- > mm/memory.c | 4 ++-- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 8e0e3cfd9f223..e52360df87d15 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1392,7 +1392,7 @@ static int insert_pmd(struct vm_area_struct *vma, unsigned long addr, > const unsigned long pfn = fop.is_folio ? folio_pfn(fop.folio) : > fop.pfn; > > - if (write) { > + if (write && pmd_present(*pmd)) { > if (pmd_pfn(*pmd) != pfn) { > WARN_ON_ONCE(!is_huge_zero_pmd(*pmd)); > return -EEXIST; > @@ -1541,7 +1541,7 @@ static void insert_pud(struct vm_area_struct *vma, unsigned long addr, > const unsigned long pfn = fop.is_folio ? folio_pfn(fop.folio) : > fop.pfn; > > - if (write) { > + if (write && pud_present(*pud)) { > if (WARN_ON_ONCE(pud_pfn(*pud) != pfn)) > return; > entry = pud_mkyoung(*pud); > diff --git a/mm/memory.c b/mm/memory.c > index a1b5575db52ac..9a1acd057ce59 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2137,7 +2137,7 @@ static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte, > pte_t pteval = ptep_get(pte); > > if (!pte_none(pteval)) { > - if (!mkwrite) > + if (!mkwrite || !pte_present(pteval)) > return -EBUSY; Why EBUSY? because it might transitory? -- Oscar Salvador SUSE Labs