[PATCH v8 08/12] iommu/arm-smmu-v3: Seize private ASID

[Jean-Philippe Brucker]

Hi Xiang,

On Mon, Jul 06, 2020 at 08:40:27PM +0800, Xiang Zheng wrote:
> > @@ -1836,7 +1880,20 @@ static struct arm_smmu_ctx_desc *arm_smmu_alloc_shared_cd(struct mm_struct *mm)
> >  
> >  	arm_smmu_init_cd(cd);
> >  
> > +	/*
> > +	 * Serialize against arm_smmu_domain_finalise_s1() and
> > +	 * arm_smmu_domain_free() as we might need to replace the private ASID
> > +	 * from an existing CD.
> > +	 */
> > +	mutex_lock(&asid_lock);
> >  	old_cd = arm_smmu_share_asid(asid);
> > +	if (!old_cd) {
> > +		ret = xa_insert(&asid_xa, asid, cd, GFP_KERNEL);
> 
> Should we use "xa_store" here? If "asid" has already been used for private, old_cd would be NULL and
> the entry indexed by "asid" in the asid_xa remains.

Great catch, that's a bug introduced in v7. arm_smmu_share_asid() would
allocate a new asid for the private context but does not remove the old
entry. For the fix I think it looks clearer if arm_smmu_share_asid()
erases the old entry before returning.

Thanks,
Jean