linux-kernel - RE: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

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Date:   Wed, 18 Dec 2019 00:29:15 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>
CC:     Peter Xu <peterx@...hat.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Wang, Zhenyu Z" <zhenyu.z.wang@...el.com>,
        "Zhao, Yan Y" <yan.y.zhao@...el.com>
Subject: RE: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory
 tracking

> From: Paolo Bonzini <pbonzini@...hat.com>
> Sent: Wednesday, December 18, 2019 12:31 AM
> 
> On 17/12/19 17:18, Alex Williamson wrote:
> >>
> >> Alex, if you are OK we'll work on such interface and move kvmgt to use it.
> >> After it's accepted, we can also mark pages dirty through this new
> interface
> >> in Kirti's dirty page tracking series.
> > I'm not sure what you're asking for, is it an interface for the host
> > CPU to read/write the memory backing of a mapped IOVA range without
> > pinning pages?  That seems like something like that would make sense for
> > an emulation model where a page does not need to be pinned for physical
> > DMA.  If you're asking more for an interface that understands the
> > userspace driver is a VM (ie. implied using a _guest postfix on the
> > function name) and knows about GPA mappings beyond the windows
> directly
> > mapped for device access, I'd not look fondly on such a request.
> 
> No, it would definitely be the former, using IOVAs to access guest
> memory---kvmgt is currently doing the latter by calling into KVM, and
> I'm not really fond of that either.
> 

Exactly. let's work on the fix.

Thanks
Kevin