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From: "Tian, Kevin" <kevin.tian@intel.com>
To: Zhangfei Gao <zhangfei.gao@linaro.org>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>, jean-philippe <jean-philippe@linaro.org>,
	Jason Gunthorpe <jgg@nvidia.com>, "baolu.lu@linux.intel.com"
	<baolu.lu@linux.intel.com>, "Zhang, Tina" <tina.zhang@intel.com>
CC: "iommu@lists.linux.dev" <iommu@lists.linux.dev>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] iommu: Fix iommu_sva_bind_device to the same domain
Thread-Topic: [PATCH] iommu: Fix iommu_sva_bind_device to the same domain
Thread-Index: AQHaZI3ars2WxaUdb0ObfriZ3G40C7EUX32A
Date: Wed, 21 Feb 2024 07:09:24 +0000
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References: <20240221061832.430-1-zhangfei.gao@linaro.org>
In-Reply-To: <20240221061832.430-1-zhangfei.gao@linaro.org>
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> From: Zhangfei Gao <zhangfei.gao@linaro.org>
> Sent: Wednesday, February 21, 2024 2:19 PM
>=20
> The accelerator dev can provide multi-queue and bind to
> the same domain in multi-thread for better performance,
> and domain refcount takes care of it.
>=20
> 'commit 092edaddb660 ("iommu: Support mm PASID 1:n with sva domains")'
> removes the possibility, so fix it
>=20
> Fixs: '092edaddb660 ("iommu: Support mm PASID 1:n with sva domains")'
> Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
> ---
>  drivers/iommu/iommu-sva.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>=20
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> index c3fc9201d0be..a95c8f3a5407 100644
> --- a/drivers/iommu/iommu-sva.c
> +++ b/drivers/iommu/iommu-sva.c
> @@ -91,7 +91,7 @@ struct iommu_sva *iommu_sva_bind_device(struct
> device *dev, struct mm_struct *mm
>  	/* Search for an existing domain. */
>  	list_for_each_entry(domain, &mm->iommu_mm->sva_domains,
> next) {
>  		ret =3D iommu_attach_device_pasid(domain, dev, iommu_mm-
> >pasid);
> -		if (!ret) {
> +		if (!ret || ret =3D=3D -EBUSY) {
>  			domain->users++;
>  			goto out;

-EBUSY is not a right indicator for reuse.

It may simply indicate that the pasid has been used for other purposes
e.g. attached to a domain different from what the caller expects here.