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From: Thomas Gleixner <tglx@linutronix.de>
To: Feng Tang <feng.tang@intel.com>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@intel.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <peterz@infradead.org>,
	x86@kernel.org, kernel test robot <oliver.sang@intel.com>,
	linux-kernel@vger.kernel.org
Cc: Feng Tang <feng.tang@intel.com>
Subject: Re: [PATCH] x86/fpu: set X86_FEATURE_OSXSAVE feature after enabling OSXSAVE in CR4
Date: Thu, 24 Aug 2023 11:01:18 +0200	[thread overview]
Message-ID: <87r0nsddb5.ffs@tglx> (raw)
In-Reply-To: <20230823065747.92257-1-feng.tang@intel.com>

On Wed, Aug 23 2023 at 14:57, Feng Tang wrote:
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index 0bab497c9436..8ebea0d522d2 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -173,6 +173,9 @@ void fpu__init_cpu_xstate(void)
>  
>  	cr4_set_bits(X86_CR4_OSXSAVE);
>  
> +	if (!boot_cpu_has(X86_FEATURE_OSXSAVE))
> +		setup_force_cpu_cap(X86_FEATURE_OSXSAVE);

This is wrong in several aspects:

     1) You force the feature bit _before_ XSAVE is completely
        initialized. fpu__init_system_xstate() has error paths which
        disable XSAVE.

     2) This conditional should have been a red flag for you simply
        because fpu__init_cpu_xstate() is invoked on all CPUs not only
        on the BSP.

I fixed it up and added a proper comment explaining it.

  parent reply	other threads:[~2023-08-24  9:01 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-23  6:57 [PATCH] x86/fpu: set X86_FEATURE_OSXSAVE feature after enabling OSXSAVE in CR4 Feng Tang
2023-08-23 22:16 ` Edgecombe, Rick P
2023-08-24  1:46   ` Feng Tang
2023-08-24  9:01 ` Thomas Gleixner [this message]
2023-08-24 11:58   ` Feng Tang

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