linux-kernel - Re: [PATCH 2/2] KVM: VMX: Add Force Emulation Prefix for "emulate the next instruction"

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Message-ID: <6d039f9d-99d9-fa4c-170b-6225bdba302a@redhat.com>
Date:   Tue, 27 Mar 2018 11:15:46 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Nikita Leshenko <nikita.leshchenko@...cle.com>,
        Liran Alon <liran.alon@...cle.com>
Cc:     kernellwp@...il.com, rkrcmar@...hat.com, andrew.cooper3@...rix.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: VMX: Add Force Emulation Prefix for "emulate the
 next instruction"

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