linux-kernel - Re: [PATCH v8 04/26] x86/fpu/xstate: Introduce XFEATURE_MASK_KERNEL

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20dc456a8b38d5cb9af3bbc8d2ebba869a2d7a44.camel@intel.com>
Date: Thu, 4 Jan 2024 22:26:35 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Yang, Weijiang"
	<weijiang.yang@...el.com>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"seanjc@...gle.com" <seanjc@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Hansen, Dave" <dave.hansen@...el.com>
CC: "john.allen@....com" <john.allen@....com>, "peterz@...radead.org"
	<peterz@...radead.org>, "Gao, Chao" <chao.gao@...el.com>,
	"mlevitsk@...hat.com" <mlevitsk@...hat.com>
Subject: Re: [PATCH v8 04/26] x86/fpu/xstate: Introduce
 XFEATURE_MASK_KERNEL_DYNAMIC xfeature set

On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
> Define a new XFEATURE_MASK_KERNEL_DYNAMIC mask to specify the
> features
> that can be optionally enabled by kernel components. This is similar
> to
> XFEATURE_MASK_USER_DYNAMIC in that it contains optional xfeatures
> that
> can allows the FPU buffer to be dynamically sized. The difference is
> that
> the KERNEL variant contains supervisor features and will be enabled
> by
> kernel components that need them, and not directly by the user.
> Currently
> it's used by KVM to configure guest dedicated fpstate for calculating
> the xfeature and fpstate storage size etc.
> 
> The kernel dynamic xfeatures now only contain XFEATURE_CET_KERNEL,
> which
> is supported by host as they're enabled in kernel XSS MSR setting but
> relevant CPU feature, i.e., supervisor shadow stack, is not enabled
> in
> host kernel therefore it can be omitted for normal fpstate by
> default.
> 
> Remove the kernel dynamic feature from
> fpu_kernel_cfg.default_features
> so that the bits in xstate_bv and xcomp_bv are cleared and
> xsaves/xrstors
> can be optimized by HW for normal fpstate.
> 
> Suggested-by: Dave Hansen <dave.hansen@...el.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>