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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 In-Reply-To: References: <20260424191456.2679717-1-stevensd@google.com> <6369e5ce-74e3-4c68-8053-d7d7d21b6955@zytor.com> <87pl1md7h0.ffs@fw13> <87qzm2b39k.ffs@fw13> Date: Sat, 20 Jun 2026 23:59:57 +0200 Message-ID: <87pl1kna8y.ffs@fw13> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B80CC120002 X-Rspam-User: X-Stat-Signature: 94tb8qfbne3xmyay9mrp5876igwg1ggu X-HE-Tag: 1781992801-381946 X-HE-Meta: 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 NKDBhEd6 e6qGiGj7SteiKK+arMzR/sjOrAsB1mZvVtqgJJF/EH9wOLD1nkj8psDcNi1KgYdurac54emUodDgSXQNfES6EKanqFaJH2XnZWvGZJAAVg82T2ikoDMn6HWElssjdg41iL0YsdZSt3uld6Qxdv7prX3xZ8A2cCVNOCucHDQIo9hV56/ZDCdtmyAzW3dTucm/1iYqT4w3y1Uc0cJtBh8bjCVqmvn1CLR0QkudU8Z2x5XjGSsFsfjBLCThkrXszdT838IJN6sDY95TawD0rN2ia8qWBFw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 19 2026 at 22:02, David Stevens wrote: > On Fri, Jun 19, 2026 at 2:59=E2=80=AFPM Thomas Gleixner = wrote: >> If the kernel skips a whole page or more then there is a serious bug >> somewhere. I might be missing something, but again the "very unlikely" >> wording which handwaves about it is just disgustingly useless. > > FRAME_WARN accepts values up to 8192 bytes, and it can always be > ignored or simply disabled. If a stack frame is larger than 4k, then We should limit that to something sane. > it's entirely possible for the code and compiler to align in a way > where the first access in the frame skips a page in the stack. I think > we agree that such code would be highly suspect and (hopefully) would > only exist in out-of-tree drivers. We don't care about out of tree drivers. > But it's something the kernel build system accepts today. Dynamic > kernel stacks suddenly turning that into a runtime kernel panic seems > like exactly the sort of edge case that we would get yelled at for not > addressing. That's a good thing. If it breaks in tree code then those people have finally an incentive to fix the warnings sent by the robots which they ignored for a long time. If it breaks out of tree code then *SHRUG*. We guarantee not to break user space, but we don't guarantee anything for out of tree kernel hacks. Thanks, tglx