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[92.26.98.202]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453647f29bdsm36635735e9.18.2025.06.20.16.08.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Jun 2025 16:08:53 -0700 (PDT) Message-ID: <262c0fd2-ac66-4ce7-903f-4062f1fe1d6e@citrix.com> Date: Sat, 21 Jun 2025 00:08:51 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: dave.hansen@intel.com 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, kirill.shutemov@linux.intel.com, 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> Subject: Re: [PATCHv6 07/16] x86/vsyscall: Reorganize the #PF emulation code Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Stat-Signature: ch7yfxm1gsguei799tkqrx38pxe87xak X-Rspam-User: X-Rspamd-Queue-Id: 7C2BD140008 X-HE-Tag: 1750460935-702830 X-HE-Meta: U2FsdGVkX1/bpg6yIQgvuguhcmJERm1O5NZ/1XZYhAvQaCtw4bUKBeUYVzIbu3bY9uGJFpI1z+EZatN6asnGjRuSGw4AQZQZq4GQfch0REGBtsyrYqHpXnj8Bd50uSynMyKeRFNZmaju/kUp4JCYbbk5i5oHHH5pXCRm7R20d5vxFz0vSEWgzrvsHKeUAVzplJZ4KCEsKP/R44+kUS3KeRhaHA7Y+sMpMffJxz6HBfaWfrkxzkb1Wox8U238ouZMIMbot3bbXgfBOT6/+Rzr1G2UxxhC1Pl8ki4q5EGxnGpVLvzDT2yKRkQZJlKNOouOWWYctKMP2Olq2SyvqXQdAGvFswRcIhxz+eLYG3NY4rNiNAa8USh1BQZ5gAY1zpQs8+/cjZ6e+ub7B2vPAlQ8EXVS+mws3XmcSkVLNlrM8IwlwPdtD6E+5rRHn+1tnqNFvlMcPZD8lrtVX6SWR4/onWD3kRwYv0ii9EGCeo4tPCZa6wIeb7oNSmuAcC2YMcNtrK4YYwOgkQhlWwY/9JzaQcEYjlroqy3EPC9C1GWUmd9k3HBiABmKY7ZZUxvno7XfRdZpTVJ4YyK+W+t5x3bABpXnh1Ju40OfG9aI/puB5yKbpIGT6o2NfbCxhj1zidw6CNlbJYxRgMiheDyIZxCYYeG5pDcdMHCoiVigf/olYI6l4ZzEPk8QG0vjbwdYWB9PuNqBi1ixs86JQ3/Cb+OB+Dx1Bmvzjf2qq5YD/0XgfBFxfuOkkkfePU/wzOER7Rv6CojQaSQ6TkCssOGTCFOvfHU8WptFdYA/okeZhOPcmqdizyotgy84a/yN2qh/QwrgxAxJeB882+5KyYMf3ixl0cs7VIg5Uh3VhzrDZlLQEIt/Esb8A60xx42YgJ9FfPFAMqAVby+cEiFWAnI9kMzn2Irvw4B4LuneaiH4haFewYGMwR5Obeq0GWyxt7BJVpaF4T2R26479QlKteJ1a0u JPA9Zmgx OuFVo0JHes8g22dtTgPnBciVA6wPbyxVsOrU2TOV8Awh6XUv9zkT1EHsoM6Fz0ULo9FbMWnFTer1nZCGrt9c4uDRG1RBChoXkP3ccoMOF/ZNt8mLcLLfMIcF69neYxDEo2hmKyrtcda0DScdMeR9mCog8o3HDJteB/nYu+UVfgZU085ItunYWBtUa5nz+kqS3MPokk4TPd4Sv2QY2U+dQgI1lvABp1Dmu29P3EvUdNqHkZ9+/dQ1hQsED8vLde0UR61UMh6xVVYx+fsw= 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: > 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. This leads to some fun corner cases in SMAP and now LASS too for virt. ~Andrew