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Mon, 10 Nov 2025 08:25:15 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Alexander Potapenko Date: Mon, 10 Nov 2025 17:24:38 +0100 X-Gm-Features: AWmQ_blSpUzzxuUgQTtcq9gjImncZd1NpVlVJACeWgHgjGc0p5BSkakhSm40GYM Message-ID: Subject: Re: [PATCH v6 10/18] x86/mm: Physical address comparisons in fill_p*d/pte To: Maciej Wieczor-Retman Cc: xin@zytor.com, peterz@infradead.org, kaleshsingh@google.com, kbingham@kernel.org, akpm@linux-foundation.org, nathan@kernel.org, ryabinin.a.a@gmail.com, dave.hansen@linux.intel.com, bp@alien8.de, morbo@google.com, jeremy.linton@arm.com, smostafa@google.com, kees@kernel.org, baohua@kernel.org, vbabka@suse.cz, justinstitt@google.com, wangkefeng.wang@huawei.com, leitao@debian.org, jan.kiszka@siemens.com, fujita.tomonori@gmail.com, hpa@zytor.com, urezki@gmail.com, ubizjak@gmail.com, ada.coupriediaz@arm.com, nick.desaulniers+lkml@gmail.com, ojeda@kernel.org, brgerst@gmail.com, elver@google.com, pankaj.gupta@amd.com, mark.rutland@arm.com, trintaeoitogc@gmail.com, jpoimboe@kernel.org, thuth@redhat.com, pasha.tatashin@soleen.com, dvyukov@google.com, jhubbard@nvidia.com, catalin.marinas@arm.com, yeoreum.yun@arm.com, mhocko@suse.com, lorenzo.stoakes@oracle.com, samuel.holland@sifive.com, vincenzo.frascino@arm.com, bigeasy@linutronix.de, surenb@google.com, ardb@kernel.org, Liam.Howlett@oracle.com, nicolas.schier@linux.dev, ziy@nvidia.com, kas@kernel.org, tglx@linutronix.de, mingo@redhat.com, broonie@kernel.org, corbet@lwn.net, andreyknvl@gmail.com, maciej.wieczor-retman@intel.com, david@redhat.com, maz@kernel.org, rppt@kernel.org, will@kernel.org, luto@kernel.org, kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, linux-doc@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: B814D8000F X-Stat-Signature: 9yzapyffb5c1shf3smx3bqy7onm47krr X-Rspam-User: X-HE-Tag: 1762791916-61762 X-HE-Meta: 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 O5nPAQFJ J7Yv4yu3stkpY0OpJCafESqRDm1k52aphtvwCp0ZMzhaY8QMKYS2a7BPDwmDNJJJNmrJcW67F/vHcMnKx4X8wxpICFMFRrw+2JQVCt0XoPVDd+7v0GUliCrnmD3DNewcZ9fhcm778//oWicjoIS2tPrnq6Uuy5uZ8rtdxCTXX1dGU6Zm8MnACXAlHsXZF0nc/Xkx88oa5jeJRk43bWsrYTylacpVlfFtC0/Gz0NMVGkTZ6zQHEmagc+ohXsrtXpLq02HttmwnSeo/ZpjrOKgsOW7adMdQDSTOrGFxEjLsKQJWj/X86wA6wFa2KHWRXqoO4U61/FqIXRJFrGpg/ujlgU/71G9Aw8rb6kXhhpOR2/4Uk5fmRoBECs5p7A== 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 Wed, Oct 29, 2025 at 9:07=E2=80=AFPM Maciej Wieczor-Retman wrote: > > From: Maciej Wieczor-Retman > > Calculating page offset returns a pointer without a tag. When comparing > the calculated offset to a tagged page pointer an error is raised > because they are not equal. > > Change pointer comparisons to physical address comparisons as to avoid > issues with tagged pointers that pointer arithmetic would create. Open > code pte_offset_kernel(), pmd_offset(), pud_offset() and p4d_offset(). > Because one parameter is always zero and the rest of the function > insides are enclosed inside __va(), removing that layer lowers the > complexity of final assembly. > > Signed-off-by: Maciej Wieczor-Retman > --- > Changelog v2: > - Open code *_offset() to avoid it's internal __va(). > > arch/x86/mm/init_64.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index 0e4270e20fad..2d79fc0cf391 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -269,7 +269,10 @@ static p4d_t *fill_p4d(pgd_t *pgd, unsigned long vad= dr) > if (pgd_none(*pgd)) { > p4d_t *p4d =3D (p4d_t *)spp_getpage(); > pgd_populate(&init_mm, pgd, p4d); > - if (p4d !=3D p4d_offset(pgd, 0)) > + > + if (__pa(p4d) !=3D (pgtable_l5_enabled() ? > + __pa(pgd) : > + (unsigned long)pgd_val(*pgd) & PTE_PFN_= MASK)) Did you test with both 4- and 5-level paging? If I understand correctly, p4d and pgd are supposed to be the same under !pgtable_l5_enabled().