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From: Like Xu <like.xu.linux@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Jim Mattson <jmattson@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [DROP][PATCH] KVM: x86: Fix the #GP(0) and #UD conditions for XSETBV emulation
Date: Thu, 20 Jan 2022 15:48:19 +0800	[thread overview]
Message-ID: <92b16faf-c9a7-4be3-43f7-3450259346e9@gmail.com> (raw)
In-Reply-To: <0d7ed850-8791-42b4-ef9a-bbaa8c52279e@redhat.com>

On 17/1/2022 7:18 pm, Paolo Bonzini wrote:
> On 1/17/22 10:44, Like Xu wrote:
>>> Also, the "Fixes" tag is not really correct as the behavior was the same 
>>> before.  Rather, it fixes commit 02d4160fbd76 ("x86: KVM: add xsetbv to the 
>>
>> It seems the original code comes from 81dd35d42c9a ("KVM: SVM: Add xsetbv 
>> intercept").
>> 2acf923e38 ("KVM: VMX: Enable XSAVE/XRSTOR for guest") and 92f9895c146d.
>>
>>> emulator", 2019-08-22).  Checking OSXSAVE is a bug in the emulator path, even 
>>> though it's not needed in the XSETBV vmexit case.
>>
>> The kvm_emulate_xsetbv() has been removed from the emulator path.
>> I'm not really sure why it's not needed in the XSETBV vmexit case. More details ?
> 
> Nevermind, I confused AMD (where #UD is generated before checking for 
> exceptions) with Intel where it's unconditional.
> 
> So the bug should be there since 2acf923e38 by executing XSETBV with 
> CR4.XSAVE=0.  If so, please include a testcase.

In the testcase "executing XSETBV with CR4.XSAVE=0",

- on the VMX, #UD delivery does not require vm-exit;
- on the SVM, #UD is trapped but goes to the ud_interception() path;

There is no room to run this pointless patch.
Thank you and sorry for the noise.

> 
> Paolo
> 
>>>
>>> Thanks,
>>>
>>> Paolo
>>>
>>>> +    if ((is_protmode(vcpu) && static_call(kvm_x86_get_cpl)(vcpu) != 0) ||
>>>>           __kvm_set_xcr(vcpu, kvm_rcx_read(vcpu), kvm_read_edx_eax(vcpu))) {
>>>>           kvm_inject_gp(vcpu, 0);
>>>>           return 1;
>>>
>>>
>>
> 
> 

  reply	other threads:[~2022-01-20  7:48 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-17  7:24 [PATCH] KVM: x86: Fix the #GP(0) and #UD conditions for XSETBV emulation Like Xu
2022-01-17  8:31 ` Paolo Bonzini
2022-01-17  9:44   ` Like Xu
2022-01-17 11:18     ` Paolo Bonzini
2022-01-20  7:48       ` Like Xu [this message]
2022-01-20  9:17         ` [DROP][PATCH] " Paolo Bonzini
2022-01-20  9:31           ` Xiaoyao Li
2022-01-20  9:49             ` Paolo Bonzini

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