linux-kernel - Re: [PATCH 0/4] KVM: x86: TIF_NEED_FPU

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Message-ID: <32d432f7-bbdf-a240-7ee9-303d019d8d1a@linux.intel.com>
Date:   Wed, 4 Mar 2020 15:38:44 +0800
From:   "Liu, Jing2" <jing2.liu@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Derek Yerger <derek@....llc>,
        kernel@...dan.com, Thomas Lambertz <mail@...maslambertz.de>,
        Rik van Riel <riel@...riel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/4] KVM: x86: TIF_NEED_FPU_LOAD bug fixes


On 1/17/2020 2:26 PM, Sean Christopherson wrote:
> TIF_FPU_NEED_LOAD can be set any time
> control is transferred out of KVM, e.g. via IRQ->softirq, not just when
> KVM is preempted.

Hi Sean,

Is this just because kernel_fpu_begin() is called during softirq? I saw 
the dump trace in 3/4 message, but didn't find out clue.

Could I ask where kernel_fpu_begin() is called? Or is this just a 
"possible" thing?

Because I just want to make sure that, kvm can use this flag to cover 
all preempt/softirq/(other?) cases?

Thanks,

Jing