On 10/8/2024 8:40 AM, Jonah Palmer wrote:
On 10/8/24 2:51 AM, Eugenio Perez Martin wrote:
On Tue, Oct 8, 2024 at 2:14 AM Si-Wei Liu <si-wei....@oracle.com> wrote:
On 10/7/2024 6:51 AM, Eugenio Perez Martin wrote:
On Fri, Oct 4, 2024 at 8:48 PM Jonah Palmer
<jonah.pal...@oracle.com> wrote:
On 10/4/24 11:17 AM, Eugenio Perez Martin wrote:
On Fri, Oct 4, 2024 at 2:45 PM Jonah Palmer
<jonah.pal...@oracle.com> wrote:
Implements the IOVA->GPA tree for handling mapping, unmapping, and
translations for guest memory regions.
When the guest has overlapping memory regions, an HVA to IOVA
translation
may return an incorrect IOVA when searching the IOVA->HVA tree.
This is
due to one HVA range being contained (overlapping) in another
HVA range
in the IOVA->HVA tree. By creating an IOVA->GPA tree, we can use
GPAs to
translate and find the correct IOVA for guest memory regions.
Yes, this first patch is super close to what I meant, just one issue
and a pair of nits here and there.
I'd leave the second patch as an optimization on top, if the numbers
prove that adding the code is worth it.
Ah okay, gotcha. I also wasn't sure if what you mentioned below on
the
previous series you also wanted implemented or if these would also be
optimizations on top.
[Adding code to the vhost_iova_tree layer for handling multiple
buffers
returned from translation for the memory area where each iovec
covers]:
-----------------------------------------------------------------------
"Let's say that SVQ wants to translate the HVA range
0xfeda0000-0xfedd0000. So it makes available for the device two
chained buffers: One with addr=0x1000 len=0x20000 and the other one
with addr=(0x20000c1000 len=0x10000).
The VirtIO device should be able to translate these two buffers in
isolation and chain them. Not optimal but it helps to keep QEMU
source
clean, as the device already must support it."
This is 100% in the device and QEMU is already able to split the
buffers that way, so we don't need any change in QEMU.
Noted that if working with the full HVA tree directly, the internal
iova
tree linear iterator iova_tree_find_address_iterator() today doesn't
guarantee the iova range returned can cover the entire length of the
iov, so things could happen like that the aliased range with smaller
size (than the requested) happens to be hit first in the linear search
and be returned, the fragmentation of which can't be guarded against by
the VirtIO device or the DMA API mentioned above.
The second patch in this series kind of mitigated this side effect by
sorting out the backing ram_block with the help of
qemu_ram_block_from_host() in case of guest memory backed iov, so it
doesn't really count on vhost_iova_gpa_tree_find_iova() to find the
matching IOVA, but instead (somehow implicitly) avoids the
fragmentation
side effect as mentioned above would never happen. Not saying I like
the
way how it is implemented, but just wanted to point out the implication
if the second patch has to be removed - either add special handling
code
to the iova-tree iterator sizing the range (same as how range selection
based upon permission will be done), or add special code in SVQ
layer to
deal with fragmented IOVA ranges due to aliasing.
This special code in SVQ is already there. And it will be needed even
if we look for the buffers by GPA instead of by vaddr, the same way
virtqueue_map_desc needs to handle it even if it works with GPA.
Continuous GPA does not imply continuous vaddr.
My apologies if I misunderstood something here regarding size &
permission matching, but I attempted to implement both the size and
permission check to iova_tree_find_address_iterator(), however,
there's a sizing mismatch in the vhost_svq_translate_addr() code path
that's causing vhost-net to fail to start.
qemu-system-x86_64: unable to start vhost net: 22: falling back on
userspace virtio
More specifically, in vhost_svq_add_split(), the first call to
vhost_svq_vring_write_descs() returns false:
ok = vhost_svq_vring_write_descs(svq, sgs, out_sg, out_num, in_num >
0, false);
if (unlikely(!ok)) {
return false;
}
Maybe I misunderstood the proposal, but in
iova_tree_find_address_iterator I'm checking for an exact match for
sizes:
if (map->size != needle->size || map->perm != needle->perm) {
return false;
}
The permission needs to exact match, while the size doesn't have to. The
current iova_tree_find_address_iterator() has the following check:
if (map->translated_addr + map->size < needle->translated_addr ||
needle->translated_addr + needle->size < map->translated_addr) {
return false;
}
So essentially it does make sure the starting translated_addr on the
needle is greater than or equal to the starting translated_addr on the
map, and the first match of the map range in an ordered linear search
will be returned, but it doesn't guarantee the ending address on the
needle (needle->translated_addr + needle->size) will be covered by the
ending address on the map (map->translated_addr + map->size), so this
implementation is subjected to fragmented iova ranges with contiguous
HVA address. I don't see the current SVQ handles this well, and the
reason of iova fragmentation is due to overlapped region or memory
aliasing (unlike the GPA tree implementation, we have no additional info
to help us identify the exact IOVA when two or more overlapped HVA
ranges are given), which is orthogonal to the HVA fragmentation (with
contiguous GPA) handling in virtqueue_map_desc().
How to handle this situation? Well, I guess Eugenio may have different
opinion, but to me the only way seems to continue to search till a
well-covered IOVA range can be found, or we may have to return multiple
IOVA ranges splitting a contiguous HVA buffer...
Regards,
-Siwei
During the device setup phase, vhost_svq_add_split() ->
vhost_svq_vring_write_descs() -> vhost_svq_translate_addr() ->
vhost_iova_tree_find_iova() -> iova_tree_find_iova() is called, but in
iova_tree_find_address_iterator() map->size & needle->size mismatch. I
inserted some printf's to give more information:
...
[ 8.019672] ahci 0000:00:1f.2: 6/6 ports implemented (port mask 0x3f)
[ 8.020694] ahci 0000:00:1f.2: flags: 64bit ncq only
[ 8.022403] scsi host0: ahci
[ 8.023511] scsi host1: ahci
[ 8.024446] scsi host2: ahci
[ 8.025308
vhost_svq_translate_addr: iovec[i].iov_len = 0x8
iova_tree_find_address_iterator: mismatched sizes
map->size: 0xfff, needle->size: 0x8
map->perm: 1, needle->perm: 1
vhost_svq_add_split: _write_descs fail, sgs: 0x7fd85018ea80, out_sg:
0x7ff8649fbb50, out_num: 1, in_sg: 0x7ff8649fbb60, in_num: 1,
more_descs: true, write: false
vhost_vdpa_svq_unmap_ring
vhost_vdpa_svq_unmap_ring
vhost_vdpa_listener_region_del
vhost_vdpa_listener_region_del
vhost_vdpa_listener_region_del
vhost_vdpa_listener_region_del
vhost_vdpa_listener_region_del
vhost_vdpa_svq_unmap_ring
vhost_vdpa_svq_unmap_ring
vhost_vdpa_svq_unmap_ring
vhost_vdpa_svq_unmap_ring
2024-10-08T15:12:22.184902Z qemu-system-x86_64: unable to start vhost
net: 22: falling back on userspace virtio
] scsi host3: ahci
[ 10.921733] scsi host4: ahci
[ 10.922946] scsi host5: ahci
[ 10.923486] virtio_net virtio1 enp0s2: renamed from eth0
...
This is with similar Qemu args as Si-Wei's from way back when:
-m size=128G,slots=8,maxmem=256G
There are also some error catches with just the permission check but
it appears the vhost-net device is still able to start up (when not
matching sizes also).
