linux-kernel - Re: [PATCH] iommu: iommu_group_alloc_default_domain: Fix ops->default

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Date: Tue, 23 Jan 2024 13:49:05 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: ovidiu.panait@...driver.com
Cc: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	robin.murphy@....com, will@...nel.org, joro@...tes.org
Subject: Re: [PATCH] iommu: iommu_group_alloc_default_domain: Fix
 ops->default_domain codepath

On Tue, Jan 23, 2024 at 06:58:29PM +0200, ovidiu.panait@...driver.com wrote:
> From: Ovidiu Panait <ovidiu.panait@...driver.com>
> 
> Since commit [1], FSL_PAMU initialization on t4240rdb board fails
> with: "fsl-pamu-domain: pamu_domain_init: Can't register iommu device".
> 
> Commit [1] changed the behavior for drivers that set ops->default_domain,
> as the function iommu_group_alloc_default_domain() is now called with
> "req_type == IOMMU_DOMAIN_IDENTITY", rather than "req_type == 0". This
> causes the following EINVAL condition to be hit during FSL_PAMU
> initialization:
>   ...
>        if (ops->default_domain) {
>                if (req_type)
>                        return ERR_PTR(-EINVAL);
>                return ops->default_domain;
>        }
>   ...
> 
> To avoid this issue when ops->default_domain != NULL, remove the check for
> non-zero req_type and always return the proper default domain, as set in
> the driver.
> 
>   [1] 0f6a90436a57 ("iommu: Do not use IOMMU_DOMAIN_DMA [...]")
> 
> Fixes: 0f6a90436a57 ("iommu: Do not use IOMMU_DOMAIN_DMA if CONFIG_IOMMU_DMA is not enabled")
> Signed-off-by: Ovidiu Panait <ovidiu.panait@...driver.com>
> ---
>  drivers/iommu/iommu.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)

Oh, that is a neat combination of things

Removing the test will cause problems for the sys flow - I think the
right thing is to get the correct req_type earlier. paml wants to use
a specific domain type so it should not be switching to identity at
all.

Does the below work for you?

Also, what is your interest here? I have been wanting to delete this
driver, would your system still be OK for your usage if it was
removed?

Thanks,
Jason

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 68e648b5576706..7fa3ccdc3286e6 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -1799,7 +1799,7 @@ iommu_group_alloc_default_domain(struct iommu_group *group, int req_type)
 	 * domain. Do not use in new drivers.
 	 */
 	if (ops->default_domain) {
-		if (req_type)
+		if (req_type != ops->default_domain->type)
 			return ERR_PTR(-EINVAL);
 		return ops->default_domain;
 	}
@@ -1871,10 +1871,18 @@ static int iommu_get_def_domain_type(struct iommu_group *group,
 	const struct iommu_ops *ops = dev_iommu_ops(dev);
 	int type;
 
-	if (!ops->def_domain_type)
-		return cur_type;
-
-	type = ops->def_domain_type(dev);
+	if (ops->default_domain) {
+		/*
+		 * Drivers that declare a global static default_domain will
+		 * always choose that.
+		 */
+		type = ops->default_domain->type;
+	} else {
+		if (ops->def_domain_type)
+			type = ops->def_domain_type(dev);
+		else
+			type = cur_type;
+	}
 	if (!type || cur_type == type)
 		return cur_type;
 	if (!cur_type)