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

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Message-ID: <a3e83e6b-4bfa-3a6b-4b43-5dd451e03254@redhat.com>
Date:   Wed, 4 Dec 2019 12:04:53 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jason Wang <jasowang@...hat.com>, Peter Xu <peterx@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

On 04/12/19 11:38, Jason Wang wrote:
>>
>> +    entry = &ring->dirty_gfns[ring->dirty_index & (ring->size - 1)];
>> +    entry->slot = slot;
>> +    entry->offset = offset;
> 
> 
> Haven't gone through the whole series, sorry if it was a silly question
> but I wonder things like this will suffer from similar issue on
> virtually tagged archs as mentioned in [1].

There is no new infrastructure to track the dirty pages---it's just a
different way to pass them to userspace.

> Is this better to allocate the ring from userspace and set to KVM
> instead? Then we can use copy_to/from_user() friends (a little bit slow
> on recent CPUs).

Yeah, I don't think that would be better than mmap.

Paolo


> [1] https://lkml.org/lkml/2019/4/9/5