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References: <20220614204730.3359543-1-seanjc@google.com> <20220614204730.3359543-3-seanjc@google.com>
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From:   Jim Mattson <jmattson@google.com>
Date:   Wed, 6 Jul 2022 13:02:52 -0700
Message-ID: <CALMp9eRm_n4s-ryw5-JiD8-5S+r+F15pSFsQSqava6gHrYjJBg@mail.gmail.com>
Subject: Re: [PATCH v2 02/21] KVM: VMX: Drop bits 31:16 when shoving exception
 error code into VMCS
To:     Sean Christopherson <seanjc@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.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, Oliver Upton <oupton@google.com>,
        Peter Shier <pshier@google.com>
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On Tue, Jun 14, 2022 at 1:47 PM Sean Christopherson <seanjc@google.com> wrote:
>
> Deliberately truncate the exception error code when shoving it into the
> VMCS (VM-Entry field for vmcs01 and vmcs02, VM-Exit field for vmcs12).
> Intel CPUs are incapable of handling 32-bit error codes and will never

Never say "never." :-)

> generate an error code with bits 31:16, but userspace can provide an
> arbitrary error code via KVM_SET_VCPU_EVENTS.  Failure to drop the bits
> on exception injection results in failed VM-Entry, as VMX disallows
> setting bits 31:16.  Setting the bits on VM-Exit would at best confuse
> L1, and at worse induce a nested VM-Entry failure, e.g. if L1 decided to
> reinject the exception back into L2.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>