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[92.26.98.202]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6d0f1815dsm9554055f8f.28.2025.06.23.08.45.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 08:45:02 -0700 (PDT) Message-ID: Date: Mon, 23 Jun 2025 16:45:00 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv6 07/16] x86/vsyscall: Reorganize the #PF emulation code To: Dave Hansen , "Kirill A. Shutemov" Cc: acme@redhat.com, aik@amd.com, akpm@linux-foundation.org, alexander.shishkin@linux.intel.com, ardb@kernel.org, ast@kernel.org, bp@alien8.de, brijesh.singh@amd.com, changbin.du@huawei.com, christophe.leroy@csgroup.eu, corbet@lwn.net, daniel.sneddon@linux.intel.com, dave.hansen@linux.intel.com, ebiggers@google.com, geert+renesas@glider.be, houtao1@huawei.com, hpa@zytor.com, jgg@ziepe.ca, jgross@suse.com, jpoimboe@kernel.org, kai.huang@intel.com, kees@kernel.org, leitao@debian.org, linux-doc@vger.kernel.org, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux@rasmusvillemoes.dk, luto@kernel.org, mcgrof@kernel.org, mhiramat@kernel.org, michael.roth@amd.com, mingo@kernel.org, mingo@redhat.com, namhyung@kernel.org, paulmck@kernel.org, pawan.kumar.gupta@linux.intel.com, peterz@infradead.org, rick.p.edgecombe@intel.com, rppt@kernel.org, sandipan.das@amd.com, shijie@os.amperecomputing.com, sohil.mehta@intel.com, tglx@linutronix.de, tj@kernel.org, tony.luck@intel.com, vegard.nossum@oracle.com, x86@kernel.org, xin3.li@intel.com, xiongwei.song@windriver.com, ytcoode@gmail.com References: <9d351d80-66fe-486f-bdb3-370859dc47cc@intel.com> <262c0fd2-ac66-4ce7-903f-4062f1fe1d6e@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: CCE3BA0011 X-Stat-Signature: y1g4wtd46mea391rdwpw5hs8qqqwuipa X-HE-Tag: 1750693504-232337 X-HE-Meta: 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 CrF7xH9Q 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 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 23/06/2025 4:32 pm, Dave Hansen wrote: > On 6/23/25 05:41, Kirill A. Shutemov wrote: >> So, IIUC, that's dependency of vsyscall PF on NX. Do we want to disable >> vsyscall on boot if NX is not available? > Well, vsyscall=none can break old userspace, so forcing it on old > hardware doesn't seem like a great idea. > > But, either way, this doesn't really appear to be a LASS issue. This code: > >> if (!(error_code & X86_PF_INSTR)) { >> /* Failed vsyscall read */ >> if (vsyscall_mode == EMULATE) >> return false; > Is really asking the question: > > Is this #PF from an instruction fetch in the vsyscall page? > > That _should_ be able to be done by comparing CR2 and regs->rip. In > fact, that's done just below anyway: > > WARN_ON_ONCE(address != regs->ip); > > So I think we can fix this up with something like the attached patch > which just drives the if() from regs->rip and make the warning NX-only. Yeah, that looks good.  Furthermore, it means that the LASS #GP path (patch 9) will be consistent with this path.  (i.e. both doing a regs->rip check.) Patch Reviewed-by: Andrew Cooper if that counts for anything. ~Andrew