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Peter Anvin" , David Stevens , Pasha Tatashin , Linus Walleij , Will Deacon , Quentin Perret , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Andy Lutomirski , Xin Li , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , Kees Cook , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 00/13] Dynamic Kernel Stacks Message-ID: References: <87pl1md7h0.ffs@fw13> <87qzm2b39k.ffs@fw13> <87mrwon5uw.ffs@fw13> <87cxxgly12.ffs@fw13> <5604a47b-9457-4162-bd23-720e29cf1983@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5604a47b-9457-4162-bd23-720e29cf1983@intel.com> X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 86D4E40003 X-Rspam-User: X-Stat-Signature: dg5xbr3j49st31fhiekbsizfr3fjncd1 X-HE-Tag: 1782764287-79283 X-HE-Meta: U2FsdGVkX1/ZtvlcNu9nDcOnJQbyoioZNvTvntxd6OE99ZTDcHfcEizuqELFv3nLMZdpu5msdQcxXDwibhqOUcL0TKSQCqI4m+05NC5qcmZKh0EbsN6TsnxBF9PRv+d37fth/RcS9C26NtywDh+h0mZZxg9x+EvDhjymgycOMTpvQ91eMibrqYRukp7yzYFkxNTLDC1SPW4eKWt2qe4ZezLevK6xdHxL7Cuiw2ZCr5g02EQAYe4pz6mqb+eRrvKcK2ilf+XE3BgdMVufiSUUE/Vv7QnrDsOJOLP7d589/q1uvtZ/7uj5V3I+8D/DTqR4U3Dv6Do9ZayNj2RZm5dbKvjj7sukucPagqefAd4vviA1MtlJR8UXkbEMNo2UNyEJ2tlvJuq/93VQLtZqkWXpbXFNADRHVcv5kIIboRxeRetyzleXgydJKvhotTM7tAwg8caFLLT4vfOFJNJW9vHQ3qs1lr2Bhszan9926u9hJvYMrLgtaO3s5t/2OZ23mclgvfFRMeFootCVXK5yrAseP+boe7g0w10qCztXoPHkxTWb9h/MBpVzwg71yrClb8ubv0uUercEj5eg9m8UA9IPBZpuAZ3QrHZ6YLbTLlhXY0tJibELYaw6Ba0yBRSAQTToVR78I/oeIQS4cZOOz31QfZL1AXhGUeo5KP57W9Cn4LQklfoecfqs66rIeUJO/qcMpLIiMf/dxX3wbCnVadduR2aBvEE1CdxEN7U8kTdNMQnxzkpLnDDQsyy9DHd2kxaQ16BkVmIkZs8ZSd/0QMaUqTG23Je9IZ7pmxp6uMUQtsgAoqCK4q8yr3LuWz4wASRIpWJ8shnmH7A6m1cBcTR6OE3AqQ66JRAh8GAtkSKRl7UCJNTg1Vrr28DomKcfgfvKnqz1cADksdIRFlQHF8mAlUW0VqIWitvSVJfsXoB1Wq8q3KL+OPV3RyXl5ALFCqwleYX3JPtKODEKxZL64oS aWa0g3k/ w7+pQWfk0BAo9GeVlrs7eiX8mFytntX3yrpQo+OpelfgBwt+DWQJGBJRKdPH5qK5WPUuHuk2GFi6RRfStPTrx9TIjLreVyxZ+pbpMX1dqYOU1XZ2OdLwZHPdWtBp8DbU0ih1yhmxlCvcYUS2zMWp2ClEO+k2rspz6xbj3YUQGphnY+jzItJpQiD8ER0fisqMiJWMFtlXcP8l6372fAb4Cd+0nI5KeJAsgf+Thh5aEAVHJL9WMUPJCf60lTJ3rYwQlwYXkjw0ITtwUzH2HRRDkbl+6sw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jun 29, 2026 at 09:02:08AM -0700, Dave Hansen wrote: > It could be done with really little overhead if the vmalloc()'d stacks > set Accessed=0 on their PTEs and then checked them near vfree(). The > PTEs are already getting touched there, so the cachelines should be hot > anyway. > > The granularity would only be 4k, but it would be so cheap that we could > turn it on universally. It would also be 100% deterministic. > > There are, of course, more games that could be played with stack depth > checks on normal interrupts or NMIs. But those would be less deterministic. I mean, if we just memset64() the whole stack to 0x535441434b544f50 and then searched the stack for the lowest word that wasn't that value at process exit, we'd get a much more granular idea with vanishingly few false positives.