linux-kernel - Re: [PATCH] KVM: x86: use positive error values for msr emulation that causes #GP

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Date:   Wed, 4 Nov 2020 17:40:36 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Qian Cai <cai@...hat.com>, Maxim Levitsky <mlevitsk@...hat.com>,
        kvm@...r.kernel.org
Cc:     Borislav Petkov <bp@...en8.de>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] KVM: x86: use positive error values for msr emulation
 that causes #GP

On 04/11/20 17:31, Qian Cai wrote:
> On Sun, 2020-11-01 at 13:55 +0200, Maxim Levitsky wrote:
>> Recent introduction of the userspace msr filtering added code that uses
>> negative error codes for cases that result in either #GP delivery to
>> the guest, or handled by the userspace msr filtering.
>>
>> This breaks an assumption that a negative error code returned from the
>> msr emulation code is a semi-fatal error which should be returned
>> to userspace via KVM_RUN ioctl and usually kill the guest.
>>
>> Fix this by reusing the already existing KVM_MSR_RET_INVALID error code,
>> and by adding a new KVM_MSR_RET_FILTERED error code for the
>> userspace filtered msrs.
>>
>> Fixes: 291f35fb2c1d1 ("KVM: x86: report negative values from wrmsr emulation
>> to userspace")
>> Reported-by: Qian Cai <cai@...hat.com>
>> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> Apparently, it does not apply cleanly on today's linux-next. Paolo, is it
> possible to toss this into -next soon, so our CI won't be blocked because of
> this bug?
> 

Yep, I plan to send it to Linus later this week.

Paolo