linux-kernel - Re: [PATCH 15/17] KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers

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Message-ID: <b58d2305-284f-8652-a0f3-380b26642fe0@redhat.com>
Date:   Tue, 24 Sep 2019 02:16:36 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Andrea Arcangeli <aarcange@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Peter Xu <peterx@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/17] KVM: retpolines: x86: eliminate retpoline from
 vmx.c exit handlers

On 23/09/19 23:08, Andrea Arcangeli wrote:
> The two most attractive options to me remains what I already have
> implemented under #ifdef CONFIG_RETPOLINE with direct calls
> (optionally replacing the "if" with a small "switch" still under
> CONFIG_RETPOLINE if we give up the prioritization of the checks), or
> the replacement of kvm_vmx_exit_handlers with a switch() as suggested
> by Vitaly which would cleanup some code.
> 
> The intermediate solution that makes "const" work, has the cons of
> forcing to parse EXIT_REASON_VMCLEAR and the other vmx exit reasons
> twice, first through a pointer to function (or another if or switch
> statement) then with a second switch() statement.

I agree.  I think the way Andrea did it in his patch may not the nicest
but is (a bit surprisingly) the easiest and most maintainable.

Paolo