From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934920AbdKPNgO (ORCPT ); Thu, 16 Nov 2017 08:36:14 -0500 Received: from mail-ot0-f194.google.com ([74.125.82.194]:47173 "EHLO mail-ot0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759696AbdKPNgC (ORCPT ); Thu, 16 Nov 2017 08:36:02 -0500 X-Google-Smtp-Source: AGs4zMYZgcY5IlDvM/RKTTrV+82+8+F+bciadnu2RIdPcKSyGdCQ7wdkimuQ80N7oK3GZbtqCTd3NA== Subject: Re: [PATCH 1/2] x86,kvm: move qemu/guest FPU switching out to vcpu_run To: Paolo Bonzini , Rik van Riel , "quan.xu04@gmail.com" Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, david@redhat.com, borntraeger@de.ibm.com, tglx@linutronix.de, rkrcmar@redhat.com References: <20171114215424.32214-1-riel@redhat.com> <20171114215424.32214-2-riel@redhat.com> <2e83dd3f-8f03-03ac-45e0-f2fae1d17013@gmail.com> <1510756981.21121.291.camel@redhat.com> <1510806094.21121.303.camel@redhat.com> <0fc15536-0b34-51b6-cc14-00989825b0bc@gmail.com> <9ba2d4c1-0781-419e-ddeb-77e0494583d2@redhat.com> <00231a24-f1a2-324e-1c32-0a5a7a3995f1@redhat.com> From: Quan Xu Message-ID: Date: Thu, 16 Nov 2017 21:35:53 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <00231a24-f1a2-324e-1c32-0a5a7a3995f1@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017-11-16 20:18, Paolo Bonzini wrote: > On 16/11/2017 13:12, Quan Xu wrote: >> However it seems there is still some gap.. >> >> as Rik said, "at context switch time, the context switch code will save >> the guest FPU state to current->thread.fpu when the VCPU thread is scheduled out." > By "guest FPU state" Rik means "guest FPU with host PKRU".   :( actually it is host_pkru, just with different names.. > Guest PKRU is always stored in vcpu->arch.pkru rather than in the guest > FPU state, so guest PKRU will never be in current->thread.fpu.state either. > > KVM_GET_XSAVE will the guest FPU state with vcpu->arch.pkru and > migration will work properly.   agreed, I fix it.. that's why I concern.. there are so much methods to   write PKRU with host_pkru/guest_pkru..  after migration, KVM_GET|SET_XSAVE restore the right pkru.. but we introduce  another method: -- When the VCPU thread is scheduled back in, the context switch code will restore current->thread.fpu to the FPU registers. there is still a window to restore current->thread.fpu to the FPU registers before enter guest mode and preempt_disable(). on target machine, after migration, the pkru value is source_host_pkru in current->thread.fpu. in case,             source_host_pkru_value != guest_pkru_value,             target_host_pkru_value == guest_pkru_value.. source_host_pkru_value may be restored to PKRU.. make pkru status inconsistent.. thanks Quan Alibaba Cloud > Thanks, > > Paolo > >> after preempt_enable() in vcpu_enter_guest(), the vcpu thread is >> scheduled out, >> in kvm_x86_ops->run, the PKRU has been restored with host_pkru (IF >> guest_pkru != host_pkru).. >> instead of guest_pkru.. >> >> then the PKRU is host_pkru, how to save guest_pkru current->thread.fpu? >> >> as mentioned, all this _assumes_ that the pkru is in >> current->thread.fpu.state as well. >> >> >> thanks, >> >> Quan >> Alibaba Cloud >> >>> Context switching will only happen in vcpu_enter_guest() after >>> preempt_enable() for a preemptible kernel, or in vcpu_run via >>> cond_resched() for a non-preemptible kernel. >>> >>> Thanks, >>> >>> Paolo >>> >>>> VM migration again, in case, >>>>             source_host_pkru_value != guest_pkru_value, >>>>             target_host_pkru_value == guest_pkru_value.. >>>> >>>> the pkru status would be inconsistent.. >