linux-kernel - Re: [PATCH v8 07/26] x86/fpu/xstate: Warn if kernel dynamic xfeatures detected in normal fpstate

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Date: Wed, 03 Jan 2024 00:33:07 +0200
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com, 
	pbonzini@...hat.com, dave.hansen@...el.com, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Cc: peterz@...radead.org, chao.gao@...el.com, rick.p.edgecombe@...el.com, 
	john.allen@....com
Subject: Re: [PATCH v8 07/26] x86/fpu/xstate: Warn if kernel dynamic
 xfeatures detected in normal fpstate

On Thu, 2023-12-21 at 09:02 -0500, Yang Weijiang wrote:
> Kernel dynamic xfeatures now are __ONLY__ enabled for guest fpstate, i.e.,
> never for normal kernel fpstate. The bits are added when guest FPU config
> is initialized. Guest fpstate is allocated with fpstate->is_guest set to
> %true.
> 
> For normal fpstate, the bits should have been removed when initializes
> kernel FPU config settings, WARN_ONCE() if kernel detects normal fpstate
> xfeatures contains kernel dynamic xfeatures before executes xsaves.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
>  arch/x86/kernel/fpu/xstate.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
> index 3518fb26d06b..83ebf1e1cbb4 100644
> --- a/arch/x86/kernel/fpu/xstate.h
> +++ b/arch/x86/kernel/fpu/xstate.h
> @@ -185,6 +185,9 @@ static inline void os_xsave(struct fpstate *fpstate)
>  	WARN_ON_FPU(!alternatives_patched);
>  	xfd_validate_state(fpstate, mask, false);
>  
> +	WARN_ON_FPU(!fpstate->is_guest &&
> +		    (mask & XFEATURE_MASK_KERNEL_DYNAMIC));
> +
>  	XSTATE_XSAVE(&fpstate->regs.xsave, lmask, hmask, err);
>  
>  	/* We should never fault when copying to a kernel buffer: */

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky