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Fri, 7 Aug 2026 15:56:44 +0000 Message-ID: <0be62adf-a225-4c35-b526-6b216355797d@intel.com> Date: Fri, 7 Aug 2026 08:56:38 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 09/10] x86/fpu: Allow restoring signal frames with larger xstate_size To: Andrei Vagin CC: Andrei Vagin , Thomas Gleixner , "Ingo Molnar" , Borislav Petkov , , , Dave Hansen , , "H. Peter Anvin" References: <20260615193716.1843340-1-avagin@google.com> <20260615193716.1843340-10-avagin@google.com> <358834b6-86da-4f7f-b2b8-cda31663682d@intel.com> <1bc74033-ba54-49e1-b548-6742deedf1bf@intel.com> Content-Language: en-US From: "Chang S. 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> unenabled &= xstate_get_host_group_perm() & XFEATURE_MASK_USER_DYNAMIC; > if (unenabled) { > if (xfd_enable_feature(unenabled)) > return false; > fpstate = x86_task_fpu(current)->fpstate; > } The inner function __xfd_enable_feature() is currently invoked from two spots: (1) the #NM handler on the first userspace touch of a dynamic state, and (2) VCPU allocation when creating an AMX-enabled VM. For the latter, this was a chosen approach for the simplest AFAIK. Along with the same lines, the ptracer path deliberately does _not_ expand a ptracee's dynamic state. I would expect ptrace to be the first place to adopt such an expanding context injection. I'm not suggesting it at all; rather, the fact that ptrace does not do such suggests there has been a conscious effort to avoid adding complexity around XFD/dynamic-state management. Given that, it looks less convincing without first demonstrating that this cannot be handled in userspace. More importantly, since this would introduce yet another way for expanding the XSAVE buffer, it deserves auditing possible side-effects. Thanks, Chang