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Re: [RFC v3 1/1] memory: Skip bad range assertion if notifier supports a

From: Jason Wang
Subject: Re: [RFC v3 1/1] memory: Skip bad range assertion if notifier supports arbitrary masks
Date: Wed, 19 Aug 2020 17:36:22 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 2020/8/19 下午4:22, Eugenio Perez Martin wrote:
On Wed, Aug 19, 2020 at 9:15 AM Jason Wang <jasowang@redhat.com> wrote:

On 2020/8/18 下午10:24, Eugenio Perez Martin wrote:
On Wed, Aug 12, 2020 at 10:49 AM Eugenio Perez Martin
<eperezma@redhat.com>  wrote:
On Wed, Aug 12, 2020 at 4:24 AM Jason Wang<jasowang@redhat.com>  wrote:
On 2020/8/12 上午1:55, Eugenio Pérez wrote:
Signed-off-by: Eugenio Pérez<eperezma@redhat.com>
    hw/virtio/vhost.c     |  2 +-
    include/exec/memory.h |  2 ++
    softmmu/memory.c      | 10 ++++++++--
    3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 1a1384e7a6..e74ad9e09b 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -729,7 +729,7 @@ static void vhost_iommu_region_add(MemoryListener *listener,
        iommu_idx = memory_region_iommu_attrs_to_index(iommu_mr,
        iommu_notifier_init(&iommu->n, vhost_iommu_unmap_notify,
-                        IOMMU_NOTIFIER_UNMAP,
I think we can safely drop IOMMU_NOTIFIER_UNMAP here since device IOTLB
is sufficient.

Btw, IOMMU_NOTIFIER_IOTLB is kind of confusing, maybe something like

Got it, will change.

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 307e527835..4d94c1e984 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -87,6 +87,8 @@ typedef enum {
        /* Notify entry changes (newly created entries) */
        IOMMU_NOTIFIER_MAP = 0x2,
+    /* Notify changes on IOTLB entries */
    } IOMMUNotifierFlag;

diff --git a/softmmu/memory.c b/softmmu/memory.c
index af25987518..e2c5f6d0e7 100644
--- a/softmmu/memory.c
+++ b/softmmu/memory.c
@@ -1895,6 +1895,7 @@ void memory_region_notify_one(IOMMUNotifier *notifier,
(we probably need a better name of this function, at least something
like "memory_region_iommu_notify_one").

Ok will change.

        IOMMUNotifierFlag request_flags;
        hwaddr entry_end = entry->iova + entry->addr_mask;
+    IOMMUTLBEntry tmp = *entry;

         * Skip the notification if the notification does not overlap
@@ -1904,7 +1905,12 @@ void memory_region_notify_one(IOMMUNotifier *notifier,

-    assert(entry->iova >= notifier->start && entry_end <= notifier->end);
+    if (notifier->notifier_flags & IOMMU_NOTIFIER_IOTLB) {
+        tmp.iova = MAX(tmp.iova, notifier->start);
+        tmp.addr_mask = MIN(entry_end, notifier->end) - tmp.iova;
Any reason for doing such re-calculation here, a comment would be helpful.

It was proposed by Peter, but I understand as limiting the
address+range we pass to the notifier. Although vhost seems to support
it as long as it contains (notifier->start, notifier->end) in range, a
future notifier might not.

Yes, actually, I feel confused after reading the codes. Is
notifier->start IOVA or GPA?

In vfio.c, we did:

          iommu_notifier_init(&giommu->n, vfio_iommu_map_notify,

So it looks to me the start and end are GPA, but the assertion above
check it against IOVA which seems to be wrong ....


I see.

I didn't go so deep, I just assumed that:
* all the addresses were GPA in the vhost-net+virtio-net case,
although the name iova in IOMMUTLBEntry.
* memory region was initialized with IOVA addresses in case of VFIO.

If there's no vIOMMU, IOVA = GPA, so we're fine. But if vIOMMU is enabled, IOVA allocation is done inside guest so the start/end here not IOVA anymore.

Maybe the comment should warn about the bad "iova" name, if I'm right?

I assumed that nothing changed in the VFIO case since its notifier has
no IOMMU_NOTIFIER_DEVIOTLB flag and the new conditional in
memory_region_notify_one_iommu, but I will test with a device
passthrough and DPDK again. Do you think another test would be needed?

I'm not sure if it's easy, but it might be interesting to teach DPDK to use IOVA which is outside the range of [start, end] here.

Maybe Peter can go deeper on this.

Yes, or wait for Peter's comment.



It could be done as iommu_entry_crop(IOMMUTLBEntry *entry, const
IOMMUNotifier *notifier) though.

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