Re: [PATCH 1/2] vdpa/mlx5: Fix mr->initialized semantics
From: Si-Wei Liu
Date: Thu Aug 10 2023 - 18:21:16 EST
On 8/9/2023 8:10 PM, Jason Wang wrote:
On Thu, Aug 10, 2023 at 8:40 AM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> wrote:
On 8/8/2023 11:52 PM, Jason Wang wrote:
On Wed, Aug 9, 2023 at 6:58 AM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> wrote:
On 8/7/2023 8:00 PM, Jason Wang wrote:
On Fri, Aug 4, 2023 at 1:58 AM Si-Wei Liu <si-wei.liu@xxxxxxxxxx> wrote:
On 8/3/2023 1:03 AM, Jason Wang wrote:
On Thu, Aug 3, 2023 at 1:13 AM Dragos Tatulea <dtatulea@xxxxxxxxxx> wrote:
The mr->initialized flag is shared between the control vq and data vq
part of the mr init/uninit. But if the control vq and data vq get placed
in different ASIDs, it can happen that initializing the control vq will
prevent the data vq mr from being initialized.
This patch consolidates the control and data vq init parts into their
own init functions. The mr->initialized will now be used for the data vq
only. The control vq currently doesn't need a flag.
The uninitializing part is also taken care of: mlx5_vdpa_destroy_mr got
split into data and control vq functions which are now also ASID aware.
Fixes: 8fcd20c30704 ("vdpa/mlx5: Support different address spaces for control and data")
Signed-off-by: Dragos Tatulea <dtatulea@xxxxxxxxxx>
Reviewed-by: Eugenio Pérez <eperezma@xxxxxxxxxx>
Reviewed-by: Gal Pressman <gal@xxxxxxxxxx>
---
drivers/vdpa/mlx5/core/mlx5_vdpa.h | 1 +
drivers/vdpa/mlx5/core/mr.c | 97 +++++++++++++++++++++---------
2 files changed, 71 insertions(+), 27 deletions(-)
diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
index 25fc4120b618..a0420be5059f 100644
--- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
+++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
@@ -31,6 +31,7 @@ struct mlx5_vdpa_mr {
struct list_head head;
unsigned long num_directs;
unsigned long num_klms;
+ /* state of dvq mr */
bool initialized;
/* serialize mkey creation and destruction */
diff --git a/drivers/vdpa/mlx5/core/mr.c b/drivers/vdpa/mlx5/core/mr.c
index 03e543229791..4ae14a248a4b 100644
--- a/drivers/vdpa/mlx5/core/mr.c
+++ b/drivers/vdpa/mlx5/core/mr.c
@@ -489,60 +489,103 @@ static void destroy_user_mr(struct mlx5_vdpa_dev *mvdev, struct mlx5_vdpa_mr *mr
}
}
-void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev)
+static void _mlx5_vdpa_destroy_cvq_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
+{
+ if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] != asid)
+ return;
+
+ prune_iotlb(mvdev);
+}
+
+static void _mlx5_vdpa_destroy_dvq_mr(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
{
struct mlx5_vdpa_mr *mr = &mvdev->mr;
- mutex_lock(&mr->mkey_mtx);
+ if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
+ return;
+
if (!mr->initialized)
- goto out;
+ return;
- prune_iotlb(mvdev);
if (mr->user_mr)
destroy_user_mr(mvdev, mr);
else
destroy_dma_mr(mvdev, mr);
mr->initialized = false;
-out:
+}
+
+static void mlx5_vdpa_destroy_mr_asid(struct mlx5_vdpa_dev *mvdev, unsigned int asid)
+{
+ struct mlx5_vdpa_mr *mr = &mvdev->mr;
+
+ mutex_lock(&mr->mkey_mtx);
+
+ _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
+ _mlx5_vdpa_destroy_cvq_mr(mvdev, asid);
+
mutex_unlock(&mr->mkey_mtx);
}
-static int _mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev,
- struct vhost_iotlb *iotlb, unsigned int asid)
+void mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev)
+{
+ mlx5_vdpa_destroy_mr_asid(mvdev, mvdev->group2asid[MLX5_VDPA_CVQ_GROUP]);
+ mlx5_vdpa_destroy_mr_asid(mvdev, mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP]);
+}
+
+static int _mlx5_vdpa_create_cvq_mr(struct mlx5_vdpa_dev *mvdev,
+ struct vhost_iotlb *iotlb,
+ unsigned int asid)
+{
+ if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] != asid)
+ return 0;
+
+ return dup_iotlb(mvdev, iotlb);
This worries me as conceptually, there should be no difference between
dvq mr and cvq mr. The virtqueue should be loosely coupled with mr.
One example is that, if we only do dup_iotlb() but not try to create
dma mr here, we will break virtio-vdpa:
For this case, I guess we may need another way to support virtio-vdpa
1:1 mapping rather than overloading virtio device reset semantics, see:
https://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg953755.html
> Conceptually, the address mapping is not a part of the abstraction for
> a virtio device now. So resetting the memory mapping during virtio
> device reset seems wrong.
where we want to keep memory mapping intact across virtio device reset
for best live migration latency/downtime. I wonder would it work to
reset the mapping in vhost-vdpa life cycle out of virtio reset, say
introduce a .reset_map() op to restore 1:1 mapping within
vhost_vdpa_remove_as() right after vhost_vdpa_iotlb_unmap()? Then we can
move the iotlb reset logic to there without worry breaking virtio-vdpa.
It looks to me we don't need a new ops. We can simply do set_map()
twice
What does it mean, first set_map(0, -1ULL) with zero iotlb entry passed
in to destroy all iotlb mappings previously added, and second set_map(0,
-1ULL) to restore 1:1 DMA MR? But userspace (maybe a buggy one but
doesn't do harm) apart from vhost-vdpa itself can do unmap twice anyway,
this is supported today I think. Why there'll be such obscure
distinction, or what's the benefit to treat second .set_map() as
recreating 1:1 mapping?
Ok, I think I miss some context. I agree that it's better to decouple
memory mappings from the virtio reset. It helps to reduce the
unnecessary memory transactions. It might require a new feature flag.
This I agreed. AFAICT QEMU would need to check this new feature flag to
make sure memory mappings are kept intact across reset, otherwise for
the sake of avoid breaking older kernels it has to recreate all the
mappings after reset like how it is done today.
Regarding the method of restoring to 1:1 DMA MR, it might be dangerous
for (buggy) vhost-vDPA devices. Since its userspace doesn't set up any
mapping it can explore the kernel with that via CVQ?
Not sure I understand this proposal. The 1:1 DMA MR is first created at
vdpa device add, and gets destroyed implicitly when the first .set_map
or .dma_map call is made, which is only possible after the vhost-vdpa
module is loaded and bound to vdpa devices.
So what happens if there's a buggy userspace that doesn't do any IOTLB setup?
Then parent driver doesn't do anything in .reset_map() - as the DMA MR
is still there. Parent driver should be able to tell apart if DMA MR has
been destroyed or not by checking the internal state.
-Siwei
Thanks
Naturally the DMA MR should
be restored to how it was before when vhost-vdpa module is unloaded, or
if anything the 1:1 DMA MR creation can be deferred to until virtio-vdpa
is probed and bound to devices. Today vhost_vdpa_remove_as() as part of
the vhost-vdpa unload code path already gets all mappings purged through
vhost_vdpa_iotlb_unmap(0, -1ULL), and it should be pretty safe to
restore DMA MR via .reset_map() right after. Not sure what's the concern
here with buggy vhost-vdpa device?
Noted when vhost-vdpa is being unloaded there's even no chance to probe
kernel through CVQ, as the virtio feature is not even negotiated at that
point. And it is even trickier to wait for CVQ response from device
indefinitely when trying to unload a module.
Regards,
-Siwei
Thanks
or do you mean it would be faster?
I think with .reset_map() we at least can avoid indefinite latency
hiccup from destroying and recreating 1:1 mapping with the unwarranted
2rd unmap call. And .reset_map() should work with both .dma_map() and
.set_map() APIs with clear semantics.
Regards,
-Siwei
Thanks
Thanks,
-Siwei
commit 6f5312f801836e6af9bcbb0bdb44dc423e129206
Author: Eli Cohen <elic@xxxxxxxxxx>
Date: Wed Jun 2 11:58:54 2021 +0300
vdpa/mlx5: Add support for running with virtio_vdpa
In order to support running vdpa using vritio_vdpa driver, we need to
create a different kind of MR, one that has 1:1 mapping, since the
addresses referring to virtqueues are dma addresses.
We create the 1:1 MR in mlx5_vdpa_dev_add() only in case firmware
supports the general capability umem_uid_0. The reason for that is that
1:1 MRs must be created with uid == 0 while virtqueue objects can be
created with uid == 0 only when the firmware capability is on.
If the set_map() callback is called with new translations provided
through iotlb, the driver will destroy the 1:1 MR and create a regular
one.
Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210602085854.62690-1-elic@xxxxxxxxxx
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Thanks
+}
+
+static int _mlx5_vdpa_create_dvq_mr(struct mlx5_vdpa_dev *mvdev,
+ struct vhost_iotlb *iotlb,
+ unsigned int asid)
{
struct mlx5_vdpa_mr *mr = &mvdev->mr;
int err;
- if (mr->initialized)
+ if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] != asid)
return 0;
- if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid) {
- if (iotlb)
- err = create_user_mr(mvdev, iotlb);
- else
- err = create_dma_mr(mvdev, mr);
+ if (mr->initialized)
+ return 0;
- if (err)
- return err;
- }
+ if (iotlb)
+ err = create_user_mr(mvdev, iotlb);
+ else
+ err = create_dma_mr(mvdev, mr);
- if (mvdev->group2asid[MLX5_VDPA_CVQ_GROUP] == asid) {
- err = dup_iotlb(mvdev, iotlb);
- if (err)
- goto out_err;
- }
+ if (err)
+ return err;
mr->initialized = true;
+
+ return 0;
+}
+
+static int _mlx5_vdpa_create_mr(struct mlx5_vdpa_dev *mvdev,
+ struct vhost_iotlb *iotlb, unsigned int asid)
+{
+ int err;
+
+ err = _mlx5_vdpa_create_dvq_mr(mvdev, iotlb, asid);
+ if (err)
+ return err;
+
+ err = _mlx5_vdpa_create_cvq_mr(mvdev, iotlb, asid);
+ if (err)
+ goto out_err;
+
return 0;
out_err:
- if (mvdev->group2asid[MLX5_VDPA_DATAVQ_GROUP] == asid) {
- if (iotlb)
- destroy_user_mr(mvdev, mr);
- else
- destroy_dma_mr(mvdev, mr);
- }
+ _mlx5_vdpa_destroy_dvq_mr(mvdev, asid);
return err;
}
--
2.41.0
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