linux-kernel - Re: [PATCH 3/4] KVM: x86: Revert "KVM: X86: Fix fpu state crash in kvm guest"

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Date:   Wed, 4 Mar 2020 15:41:58 +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 3/4] KVM: x86: Revert "KVM: X86: Fix fpu state crash in
 kvm guest"


On 1/17/2020 2:26 PM, Sean Christopherson wrote:
> @@ -8198,8 +8194,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>   	trace_kvm_entry(vcpu->vcpu_id);
>   	guest_enter_irqoff();
>   
> -	/* The preempt notifier should have taken care of the FPU already.  */
> -	WARN_ON_ONCE(test_thread_flag(TIF_NEED_FPU_LOAD));
> +	fpregs_assert_state_consistent();
> +	if (test_thread_flag(TIF_NEED_FPU_LOAD))
> +		switch_fpu_return();
>   
>   	if (unlikely(vcpu->arch.switch_db_regs)) {
>   		set_debugreg(0, 7);

Can kvm be preempt out again after this (before really enter to guest)?

Thanks,

Jing