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Subject: Re: [PATCH 2/2] KVM: VMX: Add Force Emulation Prefix for "emulate the
 next instruction"
To:     Nikita Leshenko <nikita.leshchenko@oracle.com>,
        Liran Alon <liran.alon@oracle.com>
Cc:     kernellwp@gmail.com, rkrcmar@redhat.com, andrew.cooper3@citrix.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
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 <95B06D42-EFDF-4750-AD03-98D6C78378D5@oracle.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <6d039f9d-99d9-fa4c-170b-6225bdba302a@redhat.com>
Date:   Tue, 27 Mar 2018 11:15:46 +0200
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On 27/03/2018 11:05, Nikita Leshenko wrote:
> What you are essentially trying to do is create a PV interface to access
> the x86 emulator.
> Why not use a simple hypercall (VMCALL) to accomplish this instead of
> inventing yet another PV method?

Because hypercalls force you to use %rax for the hypercall number.

Paolo

> Something like “KVM_HC_EMULATE_NEXT_INSTRUCTION” in kvm_emulate_hypercall
> should do the trick (however it needs to be placed before the check for
> CPL>0 so that user mode code can test the emulator too).
> 
> Nikita