linux-kernel - Re: [PATCH v3 04/10] x86/fpu/xstate: Correct guest fpstate size calculation

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Message-ID: <Z85BdZC/tlMRxhwr@intel.com>
Date: Mon, 10 Mar 2025 09:33:41 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Chang S. Bae" <chang.seok.bae@...el.com>
CC: <tglx@...utronix.de>, <dave.hansen@...el.com>, <x86@...nel.org>,
	<seanjc@...gle.com>, <pbonzini@...hat.com>, <linux-kernel@...r.kernel.org>,
	<kvm@...r.kernel.org>, <peterz@...radead.org>, <rick.p.edgecombe@...el.com>,
	<weijiang.yang@...el.com>, <john.allen@....com>, <bp@...en8.de>
Subject: Re: [PATCH v3 04/10] x86/fpu/xstate: Correct guest fpstate size
 calculation

On Sun, Mar 09, 2025 at 03:06:19PM -0700, Chang S. Bae wrote:
>On 3/7/2025 6:49 PM, Chao Gao wrote:
>> On Fri, Mar 07, 2025 at 01:37:15PM -0800, Chang S. Bae wrote:
>> > On 3/7/2025 8:41 AM, Chao Gao wrote:
>> > > 
>> > > diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
>> > > index 6166a928d3f5..adc34914634e 100644
>> > > --- a/arch/x86/kernel/fpu/core.c
>> > > +++ b/arch/x86/kernel/fpu/core.c
>> > > @@ -218,7 +218,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
>> > >    	struct fpstate *fpstate;
>> > >    	unsigned int size;
>> > > -	size = fpu_user_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
>> > > +	size = fpu_kernel_cfg.default_size + ALIGN(offsetof(struct fpstate, regs), 64);
>> > >    	fpstate = vzalloc(size);
>> > >    	if (!fpstate)
>> > >    		return false;
>> > 
>> > BTW, did you ever base this series on the tip/master branch? The fix has
>> > already been merged there:
>> > 
>> >   1937e18cc3cf ("x86/fpu: Fix guest FPU state buffer allocation size")
>> 
>> Thanks for the information. I will remove this patch.
>
>But, I think there is a fallout that someone should follow up:
>
>The merged patch ensures size consistency between fpu_alloc_guest_fpstate()
>and fpstate_realloc(), maintaining a consistent reference to the kernel
>buffer size. However, within fpu_alloc_guest_fpstate(), fpu_guest->xfeatures
>should also be adjusted accordingly for consistency. Instead of referencing
>fpu_user_cfg, it should reference fpu_kernel_cfg.

This is fixed by the patch 3.

>
>Thanks,
>CHang
>