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X-CSE-ConnectionGUID: 58uY+RgmSY+3YcsTvpqJbg== X-CSE-MsgGUID: NEOs++VwQs2qo0McxQ53UA== X-IronPort-AV: E=McAfee;i="6700,10204,11365"; a="53072692" X-IronPort-AV: E=Sophos;i="6.14,229,1736841600"; d="scan'208";a="53072692" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Mar 2025 10:39:24 -0800 X-CSE-ConnectionGUID: ru1BalfMQ0ue0IcmsKwSpw== X-CSE-MsgGUID: QlkwuRuuT3+yDy+4eLZTEQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.14,229,1736841600"; d="scan'208";a="124317362" Received: from dnelso2-mobl.amr.corp.intel.com (HELO [10.125.110.132]) ([10.125.110.132]) by ORVIESA003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 07 Mar 2025 10:39:23 -0800 Message-ID: <74e49413-dd1a-4577-818f-b5b21b2a2b7e@intel.com> Date: Fri, 7 Mar 2025 10:39:47 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 08/10] x86/fpu/xstate: Add CET supervisor xfeature support To: Chao Gao , tglx@linutronix.de, x86@kernel.org, seanjc@google.com, pbonzini@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: peterz@infradead.org, rick.p.edgecombe@intel.com, weijiang.yang@intel.com, john.allen@amd.com, bp@alien8.de, Maxim Levitsky References: <20250307164123.1613414-1-chao.gao@intel.com> <20250307164123.1613414-9-chao.gao@intel.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/7/25 08:41, Chao Gao wrote: > From: Yang Weijiang > > To support CET virtualization, KVM needs the kernel to save/restore CET > supervisor xstate in guest FPUs when switching between guest and host > FPUs. > > Add CET supervisor xstate (i.e., XFEATURE_CET_KERNEL) support. Both the > guest FPU and the kernel FPU will allocate memory for the new xstate. > For the guest FPU, the xstate remains unused until the upcoming CET > virtualization is added to KVM. For the kernel FPU, the xstate is unused > until CET_S is enabled within the kernel. > > Note CET_S may or may not be enabled within the kernel, so always > allocating memory for XFEATURE_CET_KERNEL could potentially waste some > XSAVE buffer space. If necessary, this issue can be addressed by making > XFEATURE_CET_KERNEL a guest-only feature. I feel like these changelogs are long but say very little. This patch *WASTES* resources. Granted, it's only for a single patch, but it's totally not obvious. Could you work on tightening down the changelog, please? > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -55,7 +55,7 @@ static const char *xfeature_names[] = > "Protection Keys User registers", > "PASID state", > "Control-flow User registers", > - "Control-flow Kernel registers (unused)", > + "Control-flow Kernel registers", This should probably be: > + "Control-flow Kernel registers (KVM only)", or something similar for now. XFEATURE_CET_KERNEL is *VERY* different from all of the other features and it's silly to pretend that it's the same.