linux-kernel - Re: [PATCH v5 05/14] KVM: X86: Implement ring-based dirty memory tracking

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Message-ID: <20200310140921.GD326977@xz-x1>
Date:   Tue, 10 Mar 2020 10:09:21 -0400
From:   Peter Xu <peterx@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kbuild test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Yan Zhao <yan.y.zhao@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Christophe de Dinechin <dinechin@...hat.com>,
        Lei Cao <lei.cao@...atus.com>
Subject: Re: [PATCH v5 05/14] KVM: X86: Implement ring-based dirty memory
 tracking

On Tue, Mar 10, 2020 at 02:31:55AM -0400, Michael S. Tsirkin wrote:
> On Mon, Mar 09, 2020 at 05:35:54PM -0400, Peter Xu wrote:
> > I'll probably also
> > move KVM_DIRTY_LOG_PAGE_OFFSET==0 definition to uapi/linux/kvm.h.
> 
> 
> IMHO KVM_DIRTY_LOG_PAGE_OFFSET is kind of pointless anyway - 
> we won't be able to move data around just by changing the
> uapi value since userspace isn't
> recompiled when kernel changes ...

Yes I think we can even drop this KVM_DIRTY_LOG_PAGE_OFFSET==0
definition.  IMHO it's only a matter of whether we would like to
directly reference this value in the common code (e.g., for kernel
virt/kvm_main.c) or we want quite a few of this instead:

#ifdef KVM_DIRTY_LOG_PAGE_OFFSET
..
#endif

I slightly prefer to not use lots of "#ifdef"s so I chose to make sure
it's defined.  However I've no strong opinion on this either. So I'm
open to change that if anyone insists with some reasons.

Thanks,

-- 
Peter Xu