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From: "Bae, Chang Seok" <chang.seok.bae@intel.com>
To: "Liu, Jing2" <jing2.liu@intel.com>
Cc: "bp@suse.de" <bp@suse.de>, "luto@kernel.org" <luto@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@kernel.org" <mingo@kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"Brown, Len" <len.brown@intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"Shankar, Ravi V" <ravi.v.shankar@intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH v3 10/21] x86/fpu/xstate: Update xstate save function to support dynamic xstate
Date: Thu, 7 Jan 2021 18:40:21 +0000	[thread overview]
Message-ID: <29CB32F5-1E73-46D4-BF92-18AD05F53E8E@intel.com> (raw)
In-Reply-To: <BYAPR11MB3256BBBB24F9131D99CF7EF5A9AF0@BYAPR11MB3256.namprd11.prod.outlook.com>


> On Jan 7, 2021, at 17:41, Liu, Jing2 <jing2.liu@intel.com> wrote:
> 
> static void kvm_save_current_fpu(struct fpu *fpu)  {
> +	struct fpu *src_fpu = &current->thread.fpu;
> +
> 	/*
> 	 * If the target FPU state is not resident in the CPU registers, just
> 	 * memcpy() from current, else save CPU state directly to the target.
> 	 */
> -	if (test_thread_flag(TIF_NEED_FPU_LOAD))
> -		memcpy(&fpu->state, &current->thread.fpu.state,
> +	if (test_thread_flag(TIF_NEED_FPU_LOAD)) {
> +		memcpy(&fpu->state, &src_fpu->state,
> 		       fpu_kernel_xstate_min_size);
> For kvm, if we assume that it does not support dynamic features until this series,
> memcpy for only fpu->state is correct. 
> I think this kind of assumption is reasonable and we only make original xstate work.
> 
> -	else
> +	} else {
> +		if (fpu->state_mask != src_fpu->state_mask)
> +			fpu->state_mask = src_fpu->state_mask;
> 
> Though dynamic feature is not supported in kvm now, this function still need
> consider more things for fpu->state_mask.

Can you elaborate this? Which path might be affected by fpu->state_mask
without dynamic state supported in KVM?

> I suggest that we can set it before if...else (for both cases) and not change other. 

I tried a minimum change here.  The fpu->state_mask value does not impact the
memcpy(). So, why do we need to change it for both?

Thanks,
Chang

  reply	other threads:[~2021-01-07 18:41 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20201223155717.19556-1-chang.seok.bae@intel.com>
2020-12-23 15:56 ` [PATCH v3 01/21] x86/fpu/xstate: Modify initialization helper to handle both static and dynamic buffers Chang S. Bae
2021-01-15 12:40   ` Borislav Petkov
2020-12-23 15:56 ` [PATCH v3 03/21] x86/fpu/xstate: Modify address finders " Chang S. Bae
2021-01-15 13:06   ` Borislav Petkov
2020-12-23 15:57 ` [PATCH v3 04/21] x86/fpu/xstate: Modify context switch helpers " Chang S. Bae
2021-01-15 13:18   ` Borislav Petkov
2021-01-19 18:49     ` Bae, Chang Seok
2020-12-23 15:57 ` [PATCH v3 06/21] x86/fpu/xstate: Calculate and remember dynamic xstate buffer sizes Chang S. Bae
2021-01-22 11:44   ` Borislav Petkov
2021-01-27  1:23     ` Bae, Chang Seok
2021-01-27  9:38       ` Borislav Petkov
2021-02-03  2:54         ` Bae, Chang Seok
2020-12-23 15:57 ` [PATCH v3 10/21] x86/fpu/xstate: Update xstate save function to support dynamic xstate Chang S. Bae
2021-01-07  8:41   ` Liu, Jing2
2021-01-07 18:40     ` Bae, Chang Seok [this message]
2021-01-12  2:52       ` Liu, Jing2
2021-01-15  4:59         ` Bae, Chang Seok
2021-01-15  5:45           ` Liu, Jing2
2021-02-08 12:33   ` Borislav Petkov
2021-02-09 15:48     ` Bae, Chang Seok

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