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From: "Liu, Jing2" <jing2.liu@linux.intel.com>
To: "Bae, Chang Seok" <chang.seok.bae@intel.com>
Cc: "Liu, Jing2" <jing2.liu@intel.com>, "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: Fri, 15 Jan 2021 13:45:55 +0800	[thread overview]
Message-ID: <8178f22a-17bb-26c8-4a0b-4c459d5ef6bb@linux.intel.com> (raw)
In-Reply-To: <BFF7E955-B3BB-45A2-8A01-00ED8971C8D7@intel.com>


On 1/15/2021 12:59 PM, Bae, Chang Seok wrote:
>> On Jan 11, 2021, at 18:52, Liu, Jing2 <jing2.liu@linux.intel.com> wrote:
>>
>> On 1/8/2021 2:40 AM, Bae, Chang Seok wrote:
>>>> 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);
> <snip>
>
>>>> -	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?
>> Sure, what I'm considering is that "mask" is the first time introduced into "fpu",
>> representing the usage, so not only set it when needed, but also make it as a
>> representation, in case of anywhere using it (especially between the interval
>> of this series and kvm series in future).
> Thank you for the feedback. Sorry, I don't get any logical reason to set the
> mask always here.

Sure, I'd like to see if fx_init()->memset is the case,

though maybe no hurt so far in test.

Thanks,

Jing

>   Perhaps, KVM code can be updated like you mentioned when
> supporting the dynamic states there.
>
> Please let me know if I’m missing any functional issues.
>
> Thanks,
> Chang

  reply	other threads:[~2021-01-15  5:47 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
2021-01-12  2:52       ` Liu, Jing2
2021-01-15  4:59         ` Bae, Chang Seok
2021-01-15  5:45           ` Liu, Jing2 [this message]
2021-02-08 12:33   ` Borislav Petkov
2021-02-09 15:48     ` Bae, Chang Seok

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