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

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Message-ID: <10cc6fc6-c837-1a1a-a344-df97793b5ff5@redhat.com>
Date:   Tue, 17 Dec 2019 17:30:44 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        "Tian, Kevin" <kevin.tian@...el.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

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.

Paolo