lkml.org 
[lkml]   [2021]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v3 10/21] x86/fpu/xstate: Update xstate save function to support dynamic xstate
From
Date

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);
>> 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?

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).

Thanks,

Jing

> Thanks,
> Chang

\
 
 \ /
  Last update: 2021-01-12 03:55    [W:0.252 / U:0.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site