linux-kernel - Re: [PATCH 0/3] KVM: x86: move nested-related kvm_x86

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Message-ID: <20200417190553.GI287932@xz-x1>
Date:   Fri, 17 Apr 2020 15:05:53 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 0/3] KVM: x86: move nested-related kvm_x86_ops to a
 separate struct

On Fri, Apr 17, 2020 at 12:44:10PM -0400, Paolo Bonzini wrote:
> While this reintroduces some pointer chasing that was removed in
> afaf0b2f9b80 ("KVM: x86: Copy kvm_x86_ops by value to eliminate layer
> of indirection", 2020-03-31), the cost is small compared to retpolines
> and anyway most of the callbacks are not even remotely on a fastpath.
> In fact, only check_nested_events should be called during normal VM
> runtime.  When static calls are merged into Linux my plan is to use them
> instead of callbacks, and that will finally make things fast again by
> removing the retpolines.

Paolo,

Just out of curiousity: is there an explicit reason to not copy the
whole kvm_x86_nested_ops but use pointers (since after all we just
reworked kvm_x86_ops)?

Thanks,

-- 
Peter Xu