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Re: [PATCH] xen/arm: smmu: Set/clear IOMMU domain for device

Hi, Julien!

On 17.08.21 20:21, Julien Grall wrote:
Hi Oleksandr,

Apologies for the late answer.

On 11/08/2021 14:03, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>

When a device is assigned/de-assigned it is required to properly set
IOMMU domain used to protect the device. This assignment was missing,
thus it was not possible to de-assign the device:

(XEN) Deassigning device 0000:03:00.0 from dom2
(XEN) smmu: 0000:03:00.0:  not attached to domain 2
(XEN) d2: deassign (0000:03:00.0) failed (-3)

Fix this by assigning IOMMU domain on arm_smmu_assign_dev and reset it
to NULL on arm_smmu_deassign_dev.
I think this was introduced by commit 06d1f7a278dd "xen/arm: smmuv1: Keep track of 
S2CR state". If so, please add:

Fixes: 06d1f7a278dd ("xen/arm: smmuv1: Keep track of S2CR state")
Will do

Looking at the commit message, the IOMMU domain used to be set/unset in 
arm_smmu_{attach, detach}_dev() but Linux drop it because they now rely in the 
core IOMMU framework to track the domain.

So I agree with the new position for...

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
  xen/drivers/passthrough/arm/smmu.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/xen/drivers/passthrough/arm/smmu.c 
index c234ad9c7f1e..373d9d4d123a 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -2768,6 +2768,7 @@ static int arm_smmu_assign_dev(struct domain *d, u8 devfn,
      } else {
+        dev_iommu_domain(dev) = domain;

... this one. However...

@@ -2794,7 +2795,10 @@ static int arm_smmu_deassign_dev(struct domain *d, 
struct device *dev)
        if (domain->ref.counter == 0)
+    {
+        dev_iommu_domain(dev) = NULL;
+    }

... I think this one is incorrect because you would only unset 
dev_iommu_domain() is the refcount drop to 0. You can have multiple device in 
the same domain, so the ref.counter may not be 0.

So I think this needs to be moved outside of the if.
Yes, absolutely
Note that it is also a good practice to remove any reference (e.g. set to NULL) 
before freeing even if it doesn't much matter here.

Lastly, the file is using the Linux coding style. So { needs to be on the same 
line as the if.






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