Re: [Qemu-devel] vhost-user: broken mem regions

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Jun 25, 2014 at 09:52:09PM +0000, Damjan Marion (damarion) wrote:
> 
> On 25 Jun 2014, at 18:44, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> >> nregions: 4
> >> region:
> >> 	gpa = 0x100000000
> >> 	size = 3221225472
> >> 	ua = 0x2aab6ac00000
> > 
> > High memory, above 3 gigabytes.
> > 
> >> region:
> >> 	gpa = 0xFFFC0000
> >> 	size = 262144
> >> 	ua = 0x7fc13d200000
> > 
> > This is the BIOS.  There shouldn't be any FD for this one, it
> > is not allocated in hugetlbfs.
> > 
> >> region:
> >> 	gpa = 0x0
> >> 	size = 655360
> >> 	ua = 0x2aaaaac00000
> >> region:
> >> 	gpa = 0xC0000
> >> 	size = 3220439040
> >> 	ua = 0x2aaaaacc0000
> > 
> > Together, it's the first 3 GB of memory.
> > 
> > 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).
> > 
> >> BTW Any idea what to do with region 2, it doesn’t look like the one belonging
> >> to the same place, but qemu_get_ram_fd() returns same FD for it.
> > 
> > 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.
> 
> Problem is inside qemu_get_ram_block():
> 
> 
>     if (block && addr - block->offset < block->length) {
>         goto found;
>     }
> 
> this is true if we have > 4G of RAM allocated.

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

> 
> Any advice how to fix this?
> 
>