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Wed, 29 Apr 2026 21:44:28 +0000 Message-ID: Date: Wed, 29 Apr 2026 14:44:25 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] Revert "x86/fpu: Refine and simplify the magic number check during signal return" To: Andrei Vagin CC: Andrei Vagin , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov , Dave Hansen , , , , References: <20260429000623.3356606-1-avagin@google.com> <7c2681ee-a53c-402c-8947-e7a74f8720c8@intel.com> <3ef742fe-9761-4714-84d9-e72fabc5def1@intel.com> Content-Language: en-US From: "Chang S. 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When user-space supplies a valid, self-consistent > frame with an explicit size that older kernels accepted, and the updated > logic rejects it, which triggers a userspace regression. Sorry, I don't get your version of ABI. Eventually, XRSTOR will execute to restore the state. The kernel tracks each task's requested feature bitmap (RFBM), which determines the size. As describe SDM Vol.1, Section 13.13: An execution of an instruction in the XSAVE feature set may access any byte of any state component on which that execution operates even when saving a state component is omitted ... Given this, the kernel must ensure the backing memory is valid and sufficient. So this consistency does matter. Thanks, Chang