linux-kernel - Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by VM instructions

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Message-ID: <d6c3f238-9f63-fc80-1866-bbb685ce044a@amd.com>
Date:   Tue, 12 Jan 2021 15:05:34 -0600
From:   Wei Huang <wei.huang2@....com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, seanjc@...gle.com, joro@...tes.org,
        bp@...en8.de, tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        jmattson@...gle.com, wanpengli@...cent.com, bsd@...hat.com,
        dgilbert@...hat.com
Subject: Re: [PATCH 1/2] KVM: x86: Add emulation support for #GP triggered by
 VM instructions



On 1/12/21 5:09 AM, Maxim Levitsky wrote:
> On Tue, 2021-01-12 at 00:37 -0600, Wei Huang wrote:
>> From: Bandan Das <bsd@...hat.com>
>>
>> While running VM related instructions (VMRUN/VMSAVE/VMLOAD), some AMD
>> CPUs check EAX against reserved memory regions (e.g. SMM memory on host)
>> before checking VMCB's instruction intercept. If EAX falls into such
>> memory areas, #GP is triggered before VMEXIT. This causes problem under
>> nested virtualization. To solve this problem, KVM needs to trap #GP and
>> check the instructions triggering #GP. For VM execution instructions,
>> KVM emulates these instructions; otherwise it re-injects #GP back to
>> guest VMs.
>>
>> Signed-off-by: Bandan Das <bsd@...hat.com>
>> Co-developed-by: Wei Huang <wei.huang2@....com>
>> Signed-off-by: Wei Huang <wei.huang2@....com>
> 
> This is the ultimate fix for this bug that I had in mind,
> but I didn't dare to develop it, thinking it won't be accepted
> due to the added complexity.
> 
>  From a cursory look this look all right, and I will review
> and test this either today or tomorrow.

My tests mainly relied on the kvm-unit-test you developed (thanks BTW), 
on machines w/ and w/o CPUID_0x8000000A_EDX[28]=1. Both cases passed.

>