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.
Regards,
-Siwei
[Adding a permission check to iova_tree_find_address_iterator and match
the range by permissions]:
-----------------------------------------------------------------------
"About the permissions, maybe we can make the permissions to be part of
the lookup? Instead of returning them at iova_tree_find_iova, make
them match at iova_tree_find_address_iterator."
Ouch, I forgot this part. This is a small change we also need, can you
add it for the next version? Thanks for remind it!
But I understand that the problems with this is that we're assuming the
SVQ translation will always be done in a transient manner.
Signed-off-by: Jonah Palmer <jonah.pal...@oracle.com>
---
hw/virtio/vhost-iova-tree.c | 78 +++++++++++++++++++++++++++++++++++--
hw/virtio/vhost-iova-tree.h | 5 +++
hw/virtio/vhost-vdpa.c | 20 ++++++----
3 files changed, 92 insertions(+), 11 deletions(-)
diff --git a/hw/virtio/vhost-iova-tree.c b/hw/virtio/vhost-iova-tree.c
index 3d03395a77..e33fd56225 100644
--- a/hw/virtio/vhost-iova-tree.c
+++ b/hw/virtio/vhost-iova-tree.c
@@ -28,12 +28,15 @@ struct VhostIOVATree {
/* IOVA address to qemu memory maps. */
IOVATree *iova_taddr_map;
+
+ /* IOVA address to guest memory maps. */
+ IOVATree *iova_gpa_map;
};
/**
- * Create a new IOVA tree
+ * Create a new VhostIOVATree
*
- * Returns the new IOVA tree
+ * Returns the new VhostIOVATree
*/
VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, hwaddr iova_last)
{
@@ -44,6 +47,7 @@ VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, hwaddr
iova_last)
tree->iova_last = iova_last;
tree->iova_taddr_map = iova_tree_new();
+ tree->iova_gpa_map = iova_tree_new();
return tree;
}
@@ -53,6 +57,7 @@ VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, hwaddr
iova_last)
void vhost_iova_tree_delete(VhostIOVATree *iova_tree)
{
iova_tree_destroy(iova_tree->iova_taddr_map);
+ iova_tree_destroy(iova_tree->iova_gpa_map);
g_free(iova_tree);
}
@@ -71,7 +76,7 @@ const DMAMap *vhost_iova_tree_find_iova(const VhostIOVATree
*tree,
}
/**
- * Allocate a new mapping
+ * Allocate a new mapping in the IOVA->HVA tree
*
* @tree: The iova tree
* @map: The iova map
@@ -108,3 +113,70 @@ void vhost_iova_tree_remove(VhostIOVATree *iova_tree,
DMAMap map)
{
iova_tree_remove(iova_tree->iova_taddr_map, map);
}
+
+/**
+ * Find the IOVA address stored from a guest memory address
+ *
+ * @tree: The VhostIOVATree
+ * @map: The map with the guest memory address
+ *
+ * Return the stored mapping, or NULL if not found.
+ */
+const DMAMap *vhost_iova_gpa_tree_find_iova(const VhostIOVATree *tree,
+ const DMAMap *map)
Nit: Not an english native, but I find vhost_iova_tree should not be
broken for coherency with the rest of the functions. What about
vhost_iova_tree_find_iova_gpa, like _gpa variant?
Yea, I totally understand what you mean here and I have *no problem*
making it into vhost_iova_tree_find_iova_gpa.
Just to add my two cents on this, for what it's worth, now that we have
both an IOVA->HVA tree and a IOVA->GPA tree, coming up with function
names that operate on this new tree while conforming to the
vhost_iova_tree convention and being descriptive in the naming is a bit
difficult.
For example, to me, vhost_iova_tree_find_iova_gpa would seem a bit
misleading to me if I didn't know about it beforehand (or was just
seeing it for the first time). Like, are we finding the IOVA or GPA or
both? And what tree are we operating on?
If this was some personal code I was writing and I had free reign over
it, I personally would go with a format like:
vhost_<tree this function concerns>_tree_<action>
So a name like vhost_iova_gpa_tree_find_iova communicates to me that
we're operating on the iova_gpa (IOVA->GPA) tree and our action is to
find_iova (find the IOVA).
Similarly for something like vhost_iova_gpa_tree_remove or
vhost_iova_hva_tree_remove, etc.
But obviously this is the complete opposite of personal code and
certainly not something that's needed so I'm totally okay with renaming
it to vhost_iova_tree_find_iova_gpa :)
You're creating the patch and you (and everybody) can comment on it,
of course :).
To me, the fact that GPA is stored in a separated *tree* should be an
implementation detail not exposed by the function names. Ideally, the
user of the VhostIOVATree just knows that some entries are tagged with
the GPA and others are not. Saying otherwise, we could replace the GPA
for another struct, or merge both trees, and the API would remain
unchanged if we just add the _gpa as suffix.
Having said that, I'm happy with both names so feel free to keep yours.
+{
+ return iova_tree_find_iova(tree->iova_gpa_map, map);
+}
+
+/**
+ * Allocate new mappings in the IOVA->HVA & IOVA->GPA trees
+ *
+ * @tree: The VhostIOVATree
+ * @map: The iova map
+ * @gpa: The guest physical address (GPA)
+ *
+ * Returns:
+ * - IOVA_OK if the map fits both containers
+ * - IOVA_ERR_INVALID if the map does not make sense (like size overflow)
+ * - IOVA_ERR_NOMEM if the IOVA->HVA tree cannot allocate more space
+ *
+ * It returns an assigned iova in map->iova if return value is IOVA_OK.
+ */
+int vhost_iova_tree_map_alloc_gpa(VhostIOVATree *tree, DMAMap *map, hwaddr gpa)
+{
+ int ret;
+
+ /* Some vhost devices don't like addr 0. Skip first page */
+ hwaddr iova_first = tree->iova_first ?: qemu_real_host_page_size();
+
+ if (map->translated_addr + map->size < map->translated_addr ||
+ map->perm == IOMMU_NONE) {
+ return IOVA_ERR_INVALID;
+ }
+
+ /* Allocate a node in the IOVA->HVA tree */
+ ret = iova_tree_alloc_map(tree->iova_taddr_map, map, iova_first,
+ tree->iova_last);
Why not call vhost_iova_tree_map_alloc instead of duplicating it here?
Great question with no good answer! For some reason I thought against
putting it in there but will do that in the next series.
+ if (unlikely(ret != IOVA_OK)) {
+ return ret;
+ }
+
+ /* Insert a node in the IOVA->GPA tree */
+ map->translated_addr = gpa;
+ return iova_tree_insert(tree->iova_gpa_map, map);
+}
+
+/**
+ * Remove existing mappings from the IOVA->HVA & IOVA->GPA trees
+ *
+ * @iova_tree: The VhostIOVATree
+ * @map: The map to remove
+ */
+void vhost_iova_tree_remove_gpa(VhostIOVATree *iova_tree, DMAMap map)
+{
+ /* Remove the existing mapping from the IOVA->GPA tree */
+ iova_tree_remove(iova_tree->iova_gpa_map, map);
+
+ /* Remove the corresponding mapping from the IOVA->HVA tree */
+ iova_tree_remove(iova_tree->iova_taddr_map, map);
If we remove it blindly from both trees, we are keeping the bug, isn't it?
I think the remove should receive the "gpa" as a parameter, same as
alloc_gpa. After that, vhost_iova_tree_remove_gpa looks the right iova
into iova_gpa_map. And only after that, it removes that iova from
iova_tree_remove.
If it makes things easier it could receive (hwaddr gpa, size_t len) or
all of the info in a DMAMap. What do you think?
Initially that was my plan but this only gets called in
vhost_vdpa_listener_region_add/del and in both functions, by the time
this removal function is called, we already have the correct IOVA.
In vhost_vdpa_listener_region_add, we just allocated that IOVA and saved
it in mem_region. In vhost_vdpa_listener_region_del, we already found
the IOVA via vhost_iova_gpa_tree_find_iova prior to calling the removal
function.
But I could be misunderstanding something here. Let me know if I am.
Ok I missed that. I think you're totally right.
+}
diff --git a/hw/virtio/vhost-iova-tree.h b/hw/virtio/vhost-iova-tree.h
index 4adfd79ff0..511c6d18ae 100644
--- a/hw/virtio/vhost-iova-tree.h
+++ b/hw/virtio/vhost-iova-tree.h
@@ -23,5 +23,10 @@ const DMAMap *vhost_iova_tree_find_iova(const VhostIOVATree
*iova_tree,
const DMAMap *map);
int vhost_iova_tree_map_alloc(VhostIOVATree *iova_tree, DMAMap *map);
void vhost_iova_tree_remove(VhostIOVATree *iova_tree, DMAMap map);
+const DMAMap *vhost_iova_gpa_tree_find_iova(const VhostIOVATree *iova_tree,
+ const DMAMap *map);
+int vhost_iova_tree_map_alloc_gpa(VhostIOVATree *iova_tree, DMAMap *map,
+ hwaddr gpa);
+void vhost_iova_tree_remove_gpa(VhostIOVATree *iova_tree, DMAMap map);
#endif
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 3cdaa12ed5..591ff426e7 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -365,9 +365,16 @@ static void vhost_vdpa_listener_region_add(MemoryListener
*listener,
mem_region.size = int128_get64(llsize) - 1,
mem_region.perm = IOMMU_ACCESS_FLAG(true, section->readonly),
- r = vhost_iova_tree_map_alloc(s->iova_tree, &mem_region);
+ r = vhost_iova_tree_map_alloc_gpa(s->iova_tree, &mem_region,
+
section->offset_within_address_space);
if (unlikely(r != IOVA_OK)) {
error_report("Can't allocate a mapping (%d)", r);
+
+ /* Insertion to IOVA->GPA tree failed */
+ if (mem_region.translated_addr ==
+ section->offset_within_address_space) {
+ goto fail_map;
+ }
We can move this cleanup code into vhost_iova_tree_map_alloc_gpa, isn't it?
Sure can. We'd still need to check if vhost_iova_tree_map_alloc_gpa
returned IOVA_OK though and goto the fail label.
Yes, right.
Thanks!
goto fail;
}
@@ -386,7 +393,7 @@ static void vhost_vdpa_listener_region_add(MemoryListener
*listener,
fail_map:
if (s->shadow_data) {
- vhost_iova_tree_remove(s->iova_tree, mem_region);
+ vhost_iova_tree_remove_gpa(s->iova_tree, mem_region);
}
fail:
@@ -440,21 +447,18 @@ static void vhost_vdpa_listener_region_del(MemoryListener
*listener,
if (s->shadow_data) {
const DMAMap *result;
- const void *vaddr = memory_region_get_ram_ptr(section->mr) +
- section->offset_within_region +
- (iova - section->offset_within_address_space);
DMAMap mem_region = {
- .translated_addr = (hwaddr)(uintptr_t)vaddr,
+ .translated_addr = section->offset_within_address_space,
.size = int128_get64(llsize) - 1,
};
- result = vhost_iova_tree_find_iova(s->iova_tree, &mem_region);
+ result = vhost_iova_gpa_tree_find_iova(s->iova_tree, &mem_region);
if (!result) {
/* The memory listener map wasn't mapped */
return;
}
iova = result->iova;
- vhost_iova_tree_remove(s->iova_tree, *result);
+ vhost_iova_tree_remove_gpa(s->iova_tree, *result);
}
vhost_vdpa_iotlb_batch_begin_once(s);
/*
--
2.43.5
