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

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Date:   Mon, 02 Mar 2020 19:40:35 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...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

Paolo Bonzini <pbonzini@...hat.com> writes:

>       KVM: nVMX: Don't emulate instructions in guest mode

I just discovered that this patch breaks Hyper-V on KVM completely;
Oliver's 86f7e90ce8 ("KVM: VMX: check descriptor table exits on
instruction emulation") doesn't fix it either. The breakage manifests
itself as

 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...

-- 
Vitaly