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From:   "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
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Date:   Wed, 23 Sep 2020 15:20:27 -0700
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On 9/23/2020 3:08 PM, Dave Hansen wrote:
> On 9/23/20 3:06 PM, Yu, Yu-cheng wrote:
>> I think I'll add a check here for (r + 8) >= TASK_SIZE_MAX.  It is
>> better than getting a fault.
> 
> There's also wrmsr_safe().
> 
Yes, thanks.

Since I am going to change this to:

fpu__prepare_write(), then write to the XSAVES area.

The kernel does not expect XRSTORS to fail ("Bad FPU state detected..." 
message).  So maybe still check the address first.