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From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] vhost-user: broken mem regions
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To: "Damjan Marion (damarion)" <damarion@cisco.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>

On Wed, Jun 25, 2014 at 09:52:09PM +0000, Damjan Marion (damarion) wrote:
>=20
> On 25 Jun 2014, at 18:44, Paolo Bonzini <pbonzini@redhat.com> wrote:
>=20
> >> nregions: 4
> >> region:
> >> 	gpa =3D 0x100000000
> >> 	size =3D 3221225472
> >> 	ua =3D 0x2aab6ac00000
> >=20
> > High memory, above 3 gigabytes.
> >=20
> >> region:
> >> 	gpa =3D 0xFFFC0000
> >> 	size =3D 262144
> >> 	ua =3D 0x7fc13d200000
> >=20
> > This is the BIOS.  There shouldn't be any FD for this one, it
> > is not allocated in hugetlbfs.
> >=20
> >> region:
> >> 	gpa =3D 0x0
> >> 	size =3D 655360
> >> 	ua =3D 0x2aaaaac00000
> >> region:
> >> 	gpa =3D 0xC0000
> >> 	size =3D 3220439040
> >> 	ua =3D 0x2aaaaacc0000
> >=20
> > Together, it's the first 3 GB of memory.
> >=20
> > I understand now what you mean.  Yeah, the format should be changed
> > to include the offset (why does vhost-user need the ua at all?
> > perhaps the offset can replace the ua).
> >=20
> >> BTW Any idea what to do with region 2, it doesn=E2=80=99t look like =
the one belonging
> >> to the same place, but qemu_get_ram_fd() returns same FD for it.
> >=20
> > This must be a bug.  I would have expected qemu_get_ram_fd to return =
-1
> > here, so no descriptor should be passed to vhost-user.
>=20
> Problem is inside qemu_get_ram_block():
>=20
>=20
>     if (block && addr - block->offset < block->length) {
>         goto found;
>     }
>=20
> this is true if we have > 4G of RAM allocated.

Hmm I don't get it. Why is it always true for >4G RAM?

>=20
> Any advice how to fix this?
>=20
>=20