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Thu, 5 Mar 2026 07:56:20 +0000 Message-ID: <6e91b689-3916-44d9-ac3a-35a36586bacb@intel.com> Date: Wed, 4 Mar 2026 23:56:15 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/5] x86/vsyscall: Add vsyscall emulation for #GP Content-Language: en-US To: "H. Peter Anvin" , Dave Hansen , Dave Hansen , , Andy Lutomirski , Borislav Petkov CC: Jonathan Corbet , Shuah Khan , Thomas Gleixner , Ingo Molnar , "Peter Zijlstra" , Kiryl Shutsemau , "Brendan Jackman" , Sean Christopherson , "Nam Cao" , Cedric Xing , "Rick Edgecombe" , Andrew Cooper , Tony Luck , "Alexander Shishkin" , Maciej Wieczor-Retman , , References: <20260219233600.154313-1-sohil.mehta@intel.com> <20260219233600.154313-4-sohil.mehta@intel.com> <1383b357-2a10-4b36-afb9-42e2724faa31@intel.com> <3212161f-64b2-4825-8bcc-c36201ab6589@zytor.com> <2e3b1765-ae56-4642-8a94-61805a64497e@intel.com> From: Sohil Mehta In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR05CA0144.namprd05.prod.outlook.com (2603:10b6:a03:33d::29) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7997:EE_|IA3PR11MB8894:EE_ X-MS-Office365-Filtering-Correlation-Id: 888a04a4-b532-4f4e-9f28-08de7a8cafd0 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024; 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Peter Anvin wrote: > On March 4, 2026 5:45:48 PM PST, Dave Hansen wrote: >> On 3/4/26 16:10, Sohil Mehta wrote: >>> Vsyscall emulation has two modes of operation, specified by the >>> vsyscall={xonly, emulate} kernel command line option. The vsyscall page >>> is marked as execute-only in XONLY mode or read-execute in EMULATE mode. >> >> Is it really "marked as execute only"? We don't have a real execute-only >> paging permission on x86, the closest we've got is memory marked with a >> pkey that's got the AccessDisable bit set. >> >> I think it's _called_ execute-only because the kernel makes it behave >> like execute-only memory when it's handling the page fault. But I dobn't >> think it is super accurate to say it is "marked" as execute-only. >> Sorry about the wording. I should have looked at map_vsyscall() more carefully. As Peter said the page is not even present in XONLY mode and in EMULATE mode the PTE is marked as _USR but __NX. How about using "behaves" instead of marked? Or I could use "emulated" if you prefer that. So the above paragraph would be: Vsyscall emulation has two modes of operation, specified by the vsyscall={xonly, emulate} kernel command line option. The vsyscall page behaves as execute-only in XONLY mode and as read-execute in EMULATE mode.