On 05/19/2017 08:48 AM, Jason Wang wrote:

On 2017年05月17日 22:10, Maxime Coquelin wrote:

On 05/17/2017 04:53 AM, Jason Wang wrote:

On 2017年05月16日 23:16, Michael S. Tsirkin wrote:
On Mon, May 15, 2017 at 01:45:28PM +0800, Jason Wang wrote:

On 2017年05月13日 08:02, Michael S. Tsirkin wrote:
On Fri, May 12, 2017 at 04:21:58PM +0200, Maxime Coquelin wrote:
On 05/11/2017 08:25 PM, Michael S. Tsirkin wrote:
On Thu, May 11, 2017 at 02:32:46PM +0200, Maxime Coquelin wrote:
This patch specifies and implements the master/slave communication
to support device IOTLB in slave.

The vhost_iotlb_msg structure introduced for kernel backends is
re-used, making the design close between the two backends.

An exception is the use of the secondary channel to enable the
slave to send IOTLB miss requests to the master.

Signed-off-by: Maxime Coquelin <maxime.coque...@redhat.com>
docs/specs/vhost-user.txt | 75 +++++++++++++++++++++++++++++++++++++++++++++++
    hw/virtio/vhost-user.c    | 31 ++++++++++++++++++++
    2 files changed, 106 insertions(+)

diff --git a/docs/specs/vhost-user.txt b/docs/specs/vhost-user.txt
index 5fa7016..4a1f0c3 100644
--- a/docs/specs/vhost-user.txt
+++ b/docs/specs/vhost-user.txt
@@ -97,6 +97,23 @@ Depending on the request type, payload can be:
       log offset: offset from start of supplied file descriptor
where logging starts (i.e. where guest address 0 would be logged)
+ * An IOTLB message
+ ---------------------------------------------------------
+   | iova | size | user address | permissions flags | type |
+ ---------------------------------------------------------
+   IOVA: a 64-bit guest I/O virtual address
guest -> VM

+   Size: a 64-bit size
How do you specify "all memory"? give special meaning to size 0?
Good point, it does not support all memory currently.
It is not vhost-user specific, but general to the vhost implementation.
But iommu needs it to support passthrough.
Probably not, we will just pass the mappings in vhost_memory_region to
vhost. Its memory_size is also a __u64.

That's different since that's chunks of qemu virtual memory.


But we're in fact cache IOVA -> HVA mapping in the remote IOTLB. When passthrough mode is enabled, IOVA == GPA, so passing mappings in vhost_memory_region should be fine.

Not sure this is a good idea, because when configured in passthrough,
QEMU will see the IOMMU as enabled, so the the VIRTIO_F_IOMMU_PLATFORM
feature will be negotiated if both guest and backend support it.
So how the backend will know whether it should directly pick the
translation directly into the vhost_memory_region, or translate it
through the device IOTLB?

This no need for backend to know about this, since IOVA equals to GPA, vhost_memory_region stores IOVA -> HVA mapping. If we pass them, device IOTLB should work as usual?

Ok, I think there were a misunderstanding. I understood you said there
were no need to use the device IOTLB in this case.

Maybe the solution would be for QEMU to wrap "all memory" IOTLB updates
& invalidations to vhost_memory_regions, since the backend won't anyway
be able to perform accesses outside these regions?

This is just what I mean, you can refer Peter's series. >

The only possible "issue" with "all memory" is if you can not use a single TLB invalidation to invalidate all caches in remote TLB.

If needed, maybe we could introduce a new VHOST_IOTLB_INVALIDATE message
For older kernel backend that doesn't support it, -EINVAL will be
returned, so QEMU could handle it another way in this case.

We could, but not sure it was really needed.

I meant VHOST_IOTLB_INVALIDATE_ALL, and yes, I'm not sure this is
needed. But this is an option we have it turns out to be at some point.


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