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Tue, 30 Jun 2026 19:24:00 +0000 Message-ID: Date: Tue, 30 Jun 2026 12:23:59 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 09/10] x86/fpu: Allow restoring signal frames with larger xstate_size To: Andrei Vagin , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov CC: , , Dave Hansen , , "H. Peter Anvin" References: <20260615193716.1843340-1-avagin@google.com> <20260615193716.1843340-10-avagin@google.com> Content-Language: en-US From: "Chang S. 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This prevents > restoring signal frames that were saved on another CPU (in case of > container/process migration) with a different (larger) set of enabled > xstate features, even if the features to be restored are compatible. > > Relax this restriction by removing the strict check against user_size. > The previous commit introduced infrastructure to calculate the actual > required size based on the intersection of requested and supported > features. We now rely on that validation and only require that the > provided xstate_size is sufficient for the active features. I appreciate the effort to document the contract, add regression tests, and tighten the validation logic along with the revert fix so far in this series. But I'm wondering this bit of relaxing the checker is really necessary at this point. With APX, userspace can no longer assume that a higher XSTATE component number implies a higher offset within the XSAVE image. Going forward, migration software will likely need a more robust approach that interprets the layout and transforms the image when moving between machines with different layouts. With such translation, maybe further relaxing the kernel-side checker isn't that needed. Thanks, Chang