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

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Message-ID: <3c467967-a499-af4e-29df-ddfeb196714f@redhat.com>
Date:   Wed, 4 Mar 2020 08:58:55 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Liu, Jing2" <jing2.liu@...ux.intel.com>,
        Sean Christopherson <sean.j.christopherson@...el.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 04/03/20 08:41, Liu, Jing2 wrote:
>>       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)?

No, irqs are disabled here.

Paolo