RE: [PATCH v2 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

2022-06-15 Thread Tian, Kevin
> From: Nicolin Chen 
> Sent: Thursday, June 16, 2022 8:03 AM
> 
> Cases like VFIO wish to attach a device to an existing domain that was
> not allocated specifically from the device. This raises a condition
> where the IOMMU driver can fail the domain attach because the domain and
> device are incompatible with each other.
> 
> This is a soft failure that can be resolved by using a different domain.
> 
> Provide a dedicated errno from the IOMMU driver during attach that the
> reason attached failed is because of domain incompatability. EMEDIUMTYPE
> is chosen because it is never used within the iommu subsystem today and
> evokes a sense that the 'medium' aka the domain is incompatible.
> 
> VFIO can use this to know attach is a soft failure and it should continue
> searching. Otherwise the attach will be a hard failure and VFIO will
> return the code to userspace.
> 
> Update all drivers to return EMEDIUMTYPE in their failure paths that are
> related to domain incompatability. Also turn adjacent error prints into
> debug prints, for these soft failures, to prevent a kernel log spam.
> 
> Add kdocs describing this behavior.
> 
> Suggested-by: Jason Gunthorpe 
> Signed-off-by: Nicolin Chen 

Reviewed-by: Kevin Tian 
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Re: [PATCH v2 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

2022-06-15 Thread Nicolin Chen via iommu
On Thu, Jun 16, 2022 at 10:09:49AM +0800, Baolu Lu wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 2022/6/16 08:03, Nicolin Chen wrote:
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index 44016594831d..0dd13330fe12 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -4323,7 +4323,7 @@ static int prepare_domain_attach_device(struct 
> > iommu_domain *domain,
> >   return -ENODEV;
> > 
> >   if (dmar_domain->force_snooping && !ecap_sc_support(iommu->ecap))
> > - return -EOPNOTSUPP;
> > + return -EMEDIUMTYPE;
> > 
> >   /* check if this iommu agaw is sufficient for max mapped address */
> >   addr_width = agaw_to_width(iommu->agaw);
> > @@ -4331,10 +4331,10 @@ static int prepare_domain_attach_device(struct 
> > iommu_domain *domain,
> >   addr_width = cap_mgaw(iommu->cap);
> > 
> >   if (dmar_domain->max_addr > (1LL << addr_width)) {
> > - dev_err(dev, "%s: iommu width (%d) is not "
> > + dev_dbg(dev, "%s: iommu width (%d) is not "
> >   "sufficient for the mapped address (%llx)\n",
> >   __func__, addr_width, dmar_domain->max_addr);
> > - return -EFAULT;
> > + return -EMEDIUMTYPE;
> >   }
> >   dmar_domain->gaw = addr_width;
> 
> Can we simply remove the dev_err()? As the return value has explicitly
> explained the failure reason, putting a print statement won't help much.

Yes. As long as no one has objection, I can remove that in the next
version.
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Re: [PATCH v2 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

2022-06-15 Thread Baolu Lu

On 2022/6/16 08:03, Nicolin Chen wrote:

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 44016594831d..0dd13330fe12 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4323,7 +4323,7 @@ static int prepare_domain_attach_device(struct 
iommu_domain *domain,
return -ENODEV;
  
  	if (dmar_domain->force_snooping && !ecap_sc_support(iommu->ecap))

-   return -EOPNOTSUPP;
+   return -EMEDIUMTYPE;
  
  	/* check if this iommu agaw is sufficient for max mapped address */

addr_width = agaw_to_width(iommu->agaw);
@@ -4331,10 +4331,10 @@ static int prepare_domain_attach_device(struct 
iommu_domain *domain,
addr_width = cap_mgaw(iommu->cap);
  
  	if (dmar_domain->max_addr > (1LL << addr_width)) {

-   dev_err(dev, "%s: iommu width (%d) is not "
+   dev_dbg(dev, "%s: iommu width (%d) is not "
"sufficient for the mapped address (%llx)\n",
__func__, addr_width, dmar_domain->max_addr);
-   return -EFAULT;
+   return -EMEDIUMTYPE;
}
dmar_domain->gaw = addr_width;


Can we simply remove the dev_err()? As the return value has explicitly
explained the failure reason, putting a print statement won't help much.

Best regards,
baolu
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