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[92.26.98.202]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4535e97ac4asm142289045e9.3.2025.06.23.05.46.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 05:46:31 -0700 (PDT) Message-ID: Date: Mon, 23 Jun 2025 13:46:20 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHv6 07/16] x86/vsyscall: Reorganize the #PF emulation code To: "Kirill A. Shutemov" , Dave Hansen 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-Queue-Id: 670A040004 X-Stat-Signature: 63kcn59dapdbbg5busze9q3tj3wjso8k X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1750682793-585398 X-HE-Meta: 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 3rUhx6Xc 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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 1:41 pm, Kirill A. Shutemov wrote: > On Fri, Jun 20, 2025 at 04:21:38PM -0700, Dave Hansen wrote: >> On 6/20/25 16:08, Andrew Cooper wrote: >>>> But, the resulting code is wonky. It needs to do something more like this: >>>> >>>> if ((error_code & (X86_PF_WRITE | X86_PF_USER)) != X86_PF_USER) >>>> return false; >>>> >>>> if (error_code & X86_PF_INSTR)) >>>> return __emulate_vsyscall(regs, address); >>> To do this, LASS needs a proper interlink against NX || SMEP. >>> >>> If neither NX nor SMEP are active, the CPU does not report X86_PF_INSTR, >>> meaning that fetches are reported as plain reads. >> Interesting point. >> >> I think the easiest way to do this is just make a cpuid_deps[] entry for >> LASS and NX. If there's a CPU where LASS is available but where NX isn't >> available, we have much bigger problems on our hands. > I am not sure what I suppose to do here. > > Sohil pointed out that with LASS we get #GP on vsyscall, not #PF and PFEC > is not relevant for LASS. Correct.  That was my mistake originally. > > So, IIUC, that's dependency of vsyscall PF on NX. Do we want to disable > vsyscall on boot if NX is not available? > > BTW, why do we even support !NX on X86_64? Is there such HW? Yes.  Early P4 steppings had no NX at all. ~Andrew