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Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm: use PFN_PHYS() in phys_mem_access_prot() Message-ID: References: <20261113193812.1239880-1-ivanrwcm25@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261113193812.1239880-1-ivanrwcm25@gmail.com> X-Rspamd-Server: rspam06 X-Stat-Signature: c7o8zzy9fmiqpasotb1rnod1fweecftn X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 090B0160002 X-Rspam-User: X-HE-Tag: 1794725231-696307 X-HE-Meta: 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 ANQpdjyT 2UKyTB7PcynFYKmF47invf3LXUvklBLq/K9xI7Q3+Vac4sv9M2/0KZ1AKwLcMAZBvMhqV7toKM8Xqvb6zU+7UGZpPRUEWnrUJVHwGm1tfbDhopNEkfNtSjGaEiVSXQajbmn97Fz4iRSZ48Po7ne3LmGGVcXCIBtmjQmYDw3gbn1KsHfZqMR5249PLqkPEYodp+LKRJZAmNaFzrAyN9bIeXAdm5+inzK7QDKC12HVhtp8fei9wPNUuFxXOUDOHk5piPTrEIhFj6Rz+41/B1UN8ssIeW/EKZR/7kQoaW7CpdxAtqwbcGuhEGBhzmChGhVj77KZvkpPttwhqS1uQVEEtedYtfo1o+GJJdXk0sBhKxxefLLZr9dY5u8z0Gg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Fri, Nov 13, 2026 at 04:38:12PM -0300, Ivan Ezequiel Rodriguez wrote: > From: Iván Ezequiel Rodriguez > > phys_mem_access_prot() stores "pfn << PAGE_SHIFT" in a phys_addr_t. > The shift is evaluated as unsigned long, so on a 32-bit kernel with > CONFIG_PHYS_ADDR_T_64BIT an address above 4 GiB is truncated before > uncached_access() compares it with __pa(high_memory). > > mmap_mem_prepare() already shifts in phys_addr_t, so the mapping is > accepted and then left cacheable. PFN_PHYS() casts before the shift. > > On a MIPS32 XPA Malta guest, mmap of /dev/mem at 0xf00000000 without > O_DSYNC used the boot CCA. The same mapping with O_DSYNC was uncached. > With PFN_PHYS() both are uncached. > > Fixes: 7e6735c3578e ("/dev/mem: use phys_addr_t for physical addresses") > Cc: stable@vger.kernel.org > Signed-off-by: Iván Ezequiel Rodriguez Reviewed-by: Mike Rapoport (Microsoft) > --- > mm/char-mem.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/char-mem.c b/mm/char-mem.c > index c5761ddedbd7..53ce0034a4c1 100644 > --- a/mm/char-mem.c > +++ b/mm/char-mem.c > @@ -272,7 +272,7 @@ static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn, > unsigned long size, pgprot_t vma_prot) > { > #ifdef pgprot_noncached > - phys_addr_t offset = pfn << PAGE_SHIFT; > + phys_addr_t offset = PFN_PHYS(pfn); > > if (uncached_access(file, offset)) > return pgprot_noncached(vma_prot); > -- > 2.43.0 > -- Sincerely yours, Mike.