From: Liran Alon <liran.alon@oracle.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Vitaly Kuznetsov" <vkuznets@redhat.com>,
"Wanpeng Li" <wanpengli@tencent.com>,
"Jim Mattson" <jmattson@google.com>,
"Joerg Roedel" <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RESEND PATCH 07/13] KVM: x86: Add explicit flag for forced emulation on #UD
Date: Fri, 23 Aug 2019 18:31:32 +0300 [thread overview]
Message-ID: <B03AFFBB-3E33-4D04-8B5D-4FA3C7F385CB@oracle.com> (raw)
In-Reply-To: <20190823144423.GB6713@linux.intel.com>
> On 23 Aug 2019, at 17:44, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
>
> On Fri, Aug 23, 2019 at 04:47:14PM +0300, Liran Alon wrote:
>>
>>
>>> On 23 Aug 2019, at 4:07, Sean Christopherson <sean.j.christopherson@intel.com> wrote:
>>>
>>> Add an explicit emulation type for forced #UD emulation and use it to
>>> detect that KVM should unconditionally inject a #UD instead of falling
>>> into its standard emulation failure handling.
>>>
>>> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
>>
>> The name "forced emulation on #UD" is not clear to me.
>>
>> If I understand correctly, EMULTYPE_TRAP_UD is currently used to indicate
>> that in case the x86 emulator fails to decode instruction, the caller would
>> like the x86 emulator to fail early such that it can handle this condition
>> properly. Thus, I would rename it EMULTYPE_TRAP_DECODE_FAILURE.
>
> EMULTYPE_TRAP_UD is used when KVM intercepts a #UD from hardware. KVM
> only emulates select instructions in this case in order to minmize the
> emulator attack surface, e.g.:
>
> if (unlikely(ctxt->ud) && likely(!(ctxt->d & EmulateOnUD)))
> return EMULATION_FAILED;
>
> To enable testing of the emulator, KVM recognizes a special "opcode" that
> triggers full emulation on #UD, e.g. ctxt->ud is false when the #UD was
> triggered with the magic prefix. The prefix is only recognized when the
> module param force_emulation_prefix is toggled on, hence the name
> EMULTYPE_TRAP_UD_FORCED.
Ah-ha. This makes sense. Thanks for the explanation.
I would say it’s worth putting a comment in it in code…
>
>> But this new flag seems to do the same. So I’m left confused. I’m probably
>> missing something trivial here.
next prev parent reply other threads:[~2019-08-23 15:34 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-23 1:06 [RESEND PATCH 00/13] KVM: x86: Remove emulation_result enums Sean Christopherson
2019-08-23 1:06 ` [RESEND PATCH 01/13] KVM: x86: Relocate MMIO exit stats counting Sean Christopherson
2019-08-23 9:15 ` Vitaly Kuznetsov
2019-08-23 14:37 ` Sean Christopherson
2019-08-23 1:06 ` [RESEND PATCH 02/13] KVM: x86: Clean up handle_emulation_failure() Sean Christopherson
2019-08-23 9:23 ` Vitaly Kuznetsov
2019-08-23 12:58 ` Liran Alon
2019-08-23 1:06 ` [RESEND PATCH 03/13] KVM: x86: Refactor kvm_vcpu_do_singlestep() to remove out param Sean Christopherson
2019-08-23 9:32 ` Vitaly Kuznetsov
2019-08-23 13:05 ` Liran Alon
2019-08-23 1:07 ` [RESEND PATCH 04/13] KVM: x86: Drop EMULTYPE_NO_UD_ON_FAIL as a standalone type Sean Christopherson
2019-08-23 9:34 ` Vitaly Kuznetsov
2019-08-23 13:21 ` Liran Alon
2019-08-23 13:32 ` Liran Alon
2019-08-23 21:55 ` Sean Christopherson
2019-08-23 1:07 ` [RESEND PATCH 05/13] KVM: x86: Don't attempt VMWare emulation on #GP with non-zero error code Sean Christopherson
2019-08-23 11:51 ` Vitaly Kuznetsov
2019-08-23 13:23 ` Liran Alon
2019-08-23 1:07 ` [RESEND PATCH 06/13] KVM: x86: Move #GP injection for VMware into x86_emulate_instruction() Sean Christopherson
2019-08-23 12:27 ` Vitaly Kuznetsov
2019-08-23 13:30 ` Liran Alon
2019-08-23 1:07 ` [RESEND PATCH 07/13] KVM: x86: Add explicit flag for forced emulation on #UD Sean Christopherson
2019-08-23 13:47 ` Liran Alon
2019-08-23 14:44 ` Sean Christopherson
2019-08-23 15:31 ` Liran Alon [this message]
2019-08-23 1:07 ` [RESEND PATCH 08/13] KVM: x86: Move #UD injection for failed emulation into emulation code Sean Christopherson
2019-08-23 13:48 ` Liran Alon
2019-08-27 20:22 ` Sean Christopherson
2019-08-23 1:07 ` [RESEND PATCH 09/13] KVM: x86: Exit to userspace on emulation skip failure Sean Christopherson
2019-08-23 1:07 ` [RESEND PATCH 10/13] KVM: x86: Handle emulation failure directly in kvm_task_switch() Sean Christopherson
2019-08-23 1:07 ` [RESEND PATCH 11/13] KVM: x86: Move triple fault request into RM int injection Sean Christopherson
2019-08-23 1:07 ` [RESEND PATCH 12/13] KVM: VMX: Remove EMULATE_FAIL handling in handle_invalid_guest_state() Sean Christopherson
2019-08-23 1:07 ` [RESEND PATCH 13/13] KVM: x86: Remove emulation_result enums, EMULATE_{DONE,FAIL,USER_EXIT} Sean Christopherson
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