linux-kernel - Re: [GIT PULL] KVM changes for Linux 5.6-rc4

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Date:   Tue, 3 Mar 2020 11:58:27 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [GIT PULL] KVM changes for Linux 5.6-rc4

On 02/03/20 19:40, Vitaly Kuznetsov wrote:
> 
>  qemu-system-x86-23579 [005] 22018.775584: kvm_exit:             reason EPT_VIOLATION rip 0xfffff802987d6169 info 181 0
>  qemu-system-x86-23579 [005] 22018.775584: kvm_nested_vmexit:    rip fffff802987d6169 reason EPT_VIOLATION info1 181 info2 0 int_info 0 int_info_err 0
>  qemu-system-x86-23579 [005] 22018.775585: kvm_page_fault:       address febd0000 error_code 181
>  qemu-system-x86-23579 [005] 22018.775592: kvm_emulate_insn:     0:fffff802987d6169: f3 a5
>  qemu-system-x86-23579 [005] 22018.775593: kvm_emulate_insn:     0:fffff802987d6169: f3 a5 FAIL
>  qemu-system-x86-23579 [005] 22018.775596: kvm_inj_exception:    #UD (0x0)
> 
> We probably need to re-enable instruction emulation for something...

This is a rep movsw instruction, it shouldn't be intercepted.  I think
we have a stale ctxt->intercept because the

        /* Fields above regs are cleared together. */

comment is not true anymore since

    commit c44b4c6ab80eef3a9c52c7b3f0c632942e6489aa
    Author: Bandan Das <bsd@...hat.com>
    Date:   Wed Apr 16 12:46:12 2014 -0400

    KVM: emulate: clean up initializations in init_decode_cache

    A lot of initializations are unnecessary as they get set to
    appropriate values before actually being used. Optimize
    placement of fields in x86_emulate_ctxt

    Signed-off-by: Bandan Das <bsd@...hat.com>
    Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Paolo