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 <e177d0497f08173e7991341796aa21c2dd2ba86b.camel@redhat.com>
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From:   Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Date:   Thu, 5 Nov 2020 11:00:53 +0100
Message-ID: <CAM9Jb+gCoxFXh3oBnZhj8LJ6PoAy0wmQuKHR5p=sqGHyqsUe8A@mail.gmail.com>
Subject: Re: [PATCH] KVM: x86: use positive error values for msr emulation
 that causes #GP
To:     Maxim Levitsky <mlevitsk@redhat.com>
Cc:     kvm@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@vger.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Joerg Roedel <joro@8bytes.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Ingo Molnar <mingo@redhat.com>, Qian Cai <cai@redhat.com>
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> > This looks good to me. This should solve "-EPERM" return by "__kvm_set_msr" .
> >
> > A question I have, In the case of "kvm_emulate_rdmsr()",  for "r" we
> > are injecting #GP.
> > Is there any possibility of this check to be hit and still result in #GP?
>
> When I wrote this patch series I assumed that msr reads usually don't have
> side effects so they shouldn't fail, and fixed only the msr write code path
> to deal with negative errors. Now that you put this in this light,
> I do think that you are right and I should have added code for both msr reads and writes
> especially to catch cases in which negative errors are returned by mistake
> like this one (my mistake in this case since my patch series was merged
> after the userspace msrs patch series).
>
> What do you think?
>
> I can prepare a separate patch for this, which should go to the next
> kernel version since this doesn't fix a regression.

Patch on the top should be okay. I think.

Thanks,
Pankaj