linux-kernel - Re: [PATCH] iommu: Fix iommu_sva_bind

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Date: Wed, 21 Feb 2024 15:57:18 +0800
From: Zhangfei Gao <zhangfei.gao@...aro.org>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	jean-philippe <jean-philippe@...aro.org>, Jason Gunthorpe <jgg@...dia.com>, 
	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>, "Zhang, Tina" <tina.zhang@...el.com>, 
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu: Fix iommu_sva_bind_device to the same domain

On Wed, 21 Feb 2024 at 15:09, Tian, Kevin <kevin.tian@...el.com> wrote:
>
> > From: Zhangfei Gao <zhangfei.gao@...aro.org>
> > Sent: Wednesday, February 21, 2024 2:19 PM
> >
> > 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.
> >
> > 'commit 092edaddb660 ("iommu: Support mm PASID 1:n with sva domains")'
> > removes the possibility, so fix it
> >
> > Fixs: '092edaddb660 ("iommu: Support mm PASID 1:n with sva domains")'
> > Signed-off-by: Zhangfei Gao <zhangfei.gao@...aro.org>
> > ---
> >  drivers/iommu/iommu-sva.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > 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 = iommu_attach_device_pasid(domain, dev, iommu_mm-
> > >pasid);
> > -             if (!ret) {
> > +             if (!ret || ret == -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.

Thanks Kevin.

How about this

diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
index c3fc9201d0be..20b232c7675d 100644
--- a/drivers/iommu/iommu-sva.c
+++ b/drivers/iommu/iommu-sva.c
@@ -141,8 +141,8 @@ void iommu_sva_unbind_device(struct iommu_sva *handle)
        struct device *dev = handle->dev;

        mutex_lock(&iommu_sva_lock);
-       iommu_detach_device_pasid(domain, dev, iommu_mm->pasid);
        if (--domain->users == 0) {
+               iommu_detach_device_pasid(domain, dev, iommu_mm->pasid);
                list_del(&domain->next);
                iommu_domain_free(domain);
        }

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index d14413916f93..a16ade93db25 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -3551,7 +3551,7 @@ int iommu_attach_device_pasid(struct iommu_domain *domain,
        mutex_lock(&group->mutex);
        curr = xa_cmpxchg(&group->pasid_array, pasid, NULL, domain, GFP_KERNEL);
        if (curr) {
-               ret = xa_err(curr) ? : -EBUSY;
+               ret = xa_err(curr) ? : 0;
                goto out_unlock;
        }

if pasid is already attached, does not treat as error,
and domain->user++ in iommu_sva_bind_device.

Thanks