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Subject: Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking
To:     Jason Wang <jasowang@redhat.com>, Peter Xu <peterx@redhat.com>,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>
References: <20191129213505.18472-1-peterx@redhat.com>
 <20191129213505.18472-5-peterx@redhat.com>
 <1355422f-ab62-9dc3-2b48-71a6e221786b@redhat.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <a3e83e6b-4bfa-3a6b-4b43-5dd451e03254@redhat.com>
Date:   Wed, 4 Dec 2019 12:04:53 +0100
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On 04/12/19 11:38, Jason Wang wrote:
>>
>> +=C2=A0=C2=A0=C2=A0 entry =3D &ring->dirty_gfns[ring->dirty_index & (rin=
g->size - 1)];
>> +=C2=A0=C2=A0=C2=A0 entry->slot =3D slot;
>> +=C2=A0=C2=A0=C2=A0 entry->offset =3D offset;
>=20
>=20
> 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