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Howlett" , Vlastimil Babka , Mike Rapoport , 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: rspam03 X-Rspamd-Queue-Id: 9382A100005 X-Stat-Signature: bt1mscwgdowupea497z1xy8ajff6coue X-Rspam-User: 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-HE-Tag: 1794745667-948251 X-HE-Meta: U2FsdGVkX19L9BFXTf5jBpCVY7F0E3+ofci9rjginN+OLPFaL9sUqHs3Dcb4ZVLKloIhjipF07+x8khyCGWyPdhI8bdxCC+wl7Hj2Lgr5fsgTBIX+sh8i9Rzjqa87eetn7yHpZhEZB7OXGDSmDO4alwWgH2DR1e+dgPpwJaRVyX3tR0fysu0bURtjUbCG5c1Bss6/4xB0raeIvsVXK/4NirK3MzbchYLmNDDeIMDQA4QOG8gcW9A0/BIQJXxT2qnrcy8qrA7q4iVq7vIeYPx2uwLFNy0ZjAHOSkpOSFLfvZONliMZZNEPiIbrzq2eFislXFFAXYupTN51zV256mChB7Tfwe6D/sNHKEj/h2eV8im+ZStyCQOSrIeCcD7heis9WKk1yQtSX/xMK15C2GcenHWr+tjePY+Z+wJYR1q4/uDtI/Mb20rquvFk+BSbuxffhCXf69nJ5anmaG5pQUvJdQtm/pmnZnZSNVflIEO2CMstphu+RjP2skWnKo16KSkTjdB2l1UrNXOpzzz7kTuF4MyIloWwHDBLsOUHweb7zNh4ZJSYEGj6/wIye2B7J6lBxift2GOh/PTEyfPUPy3ysvplXYzdCom2PmyeZ/PEkKjSuGevemwjGpXBczWzRxqHM/geEEGBwGdgSGJKefpUEOHR6nCji/PeWWk2IMP24SnYI1kd8AvM4jCEq/DICyMJcIxPiwg7a1+VO4x3lO+z+no9aw1CYaFyhrmHhfQIXSCbSNncqJ0cCpol61cPqgDGzNIcjF4ztXqL5FXIUQhlH+ksv2GS03MTrpgb9rxFgUsebMJHPKLTmIwaios9J9JS7i5fIa2AbBJV9rUST0bxMGjwqIC2pqZKk8wFrlk5rc6QXPMVtpM/PiZ9y/VGD4N/O2Hymw5AXVCIeNTg5HZPHmzHT7BA7uGWb8sYVW3i9J5FqKrPrn49fDEHehSlcYWIx0NDbhDWL4t8IlXzhf nAEsH8ty ryG9/qt8N0Ro4OnAsFPzZe5oMqDlXohocg9j7JYEKuYAWvtM4UFRe2Ji8UGUBTD0cIDIrRxvz8Vj9oNIUT1pEIuO7tpacm4qk6VEBY58E4nYBSgB8vM6u6ACgkWo/Et+rc1VTw4UR+c+K6vYuqTgbLLleeBI1Y/7iTdYWZEKuNmqy2gg4VDR7vfvPcbJKCaBYjSW0j+O+ocWSc2lp+8qxKBoGGTSifbGGKfGUtMxS/LGl9NA7daLDbSmp2QHb2kYE/576fvE6TXzuhlsFKKu234r5GT5r9T4S2q1I/4oj3NXOyFM9ho4oKp2o7SuPsLWkYNVMtgGHSBTbO6mczQQTjxK8wmt7oUCpTnYmJHrbb7UiAsV/UmmkUMM0qw== 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 LGTM so: Reviewed-by: Lorenzo Stoakes (ARM) > --- > 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 > -- Cheers, Lorenzo