linux-kernel - Re: [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to vcpu

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Message-ID: <3da8f4f3-3db1-0c25-9e0e-4d8881145205@gmail.com>
Date:   Fri, 17 Nov 2017 10:54:50 +0800
From:   Quan Xu <quan.xu0@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        "quan.xu04@...il.com" <quan.xu04@...il.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        david@...hat.com, borntraeger@...ibm.com, tglx@...utronix.de,
        rkrcmar@...hat.com
Subject: Re: [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to
 vcpu_run



On 2017-11-17 01:50, Paolo Bonzini wrote:
> On 16/11/2017 15:28, Quan Xu wrote:
>>   	vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
>>   
>> + kvm_load_guest_fpu(vcpu);
>> +
>>   	for (;;) {
>>   		if (kvm_vcpu_running(vcpu)) {
>>   			r = vcpu_enter_guest(vcpu);
>>
>> <<
>>
>>
>>
>>    as Rik dropped  kvm_load_guest_fpu(vcpu) in  vcpu_enter_guest() ..
>>    in case still in kvm mode, how to make sure to pkru is always the
>> right one before enter guest mode, not be preempted before
>> preempt_disable()  after migration? :(
> As you know:
>
> 1) kvm_load_guest_fpu doesn't load the guest PKRU, it keeps the
> userspace PKRU.
>
> 2) the guest PKRU is only ever set in a preemption-disabled area
>
> Thus, context switch always sees the userspace PKRU.  The guest PKRU is
> only set the next time vmx_vcpu_run executes.
>
> Paolo
>

Paolo, thanks for your explanation!!:-)
Rik, could you cc me in v2?

Quan