linux-kernel - Re: [PATCH v2 06/13] KVM: x86: Refactor emulate tracepoint to explicitly take context

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Date:   Tue, 3 Mar 2020 18:44:13 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/13] KVM: x86: Refactor emulate tracepoint to
 explicitly take context

On 03/03/20 18:42, Sean Christopherson wrote:
>> As long as we have one use of vcpu, I'd rather skip this patch and
>> adjust patch 8 to use "->".  Even the other "explicitly take context"
>> parts are kinda debatable since you still have to do emul_to_vcpu.
>> Throwing a handful of
>>
>> - 	struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
>> + 	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
>>
>> into patch 8 is not bad at all and limits the churn.
> Hmm, I'd prefer to explicitly pass @ctxt, even for the tracepoint.  I get
> that it's technically unnecessary churn, but explicitly passing @ctxt means
> that every funcition that grabs arch.emulate_ctxt (all three of 'em) checks
> for a NULL ctxt.  That makes it trivial to visually audit that there's no
> risk of a bad pointer dereference, and IMO having @ctxt in the prototype
> is helpful to see "oh, this helper is called from within the emulator".
> 

That's a good rationale, but I believe this refactoring belongs more in
the "disable emulator" part than this one.

Paolo