Messages in this thread | | | Date | Thu, 9 Jun 2022 17:06:44 +0000 | From | "Raj, Ashok" <> | Subject | Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support |
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On Thu, Jun 09, 2022 at 03:08:10PM +0800, Lu Baolu wrote: > The IOMMU page tables are updated using iommu_map/unmap() interfaces. > Currently, there is no mandatory requirement for drivers to use locks > to ensure concurrent updates to page tables, because it's assumed that > overlapping IOVA ranges do not have concurrent updates. Therefore the > IOMMU drivers only need to take care of concurrent updates to level > page table entries.
The last part doesn't read well.. s/updates to level page table entries/ updates to page-table entries at the same level
> > But enabling new features challenges this assumption. For example, the > hardware assisted dirty page tracking feature requires scanning page > tables in interfaces other than mapping and unmapping. This might result > in a use-after-free scenario in which a level page table has been freed > by the unmap() interface, while another thread is scanning the next level > page table. > > This adds RCU-protected page free support so that the pages are really > freed and reused after a RCU grace period. Hence, the page tables are > safe for scanning within a rcu_read_lock critical region. Considering > that scanning the page table is a rare case, this also adds a domain > flag and the RCU-protected page free is only used when this flat is set.
s/flat/flag
> > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> > --- > include/linux/iommu.h | 9 +++++++++ > drivers/iommu/iommu.c | 23 +++++++++++++++++++++++ > 2 files changed, 32 insertions(+) > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index 5e1afe169549..6f68eabb8567 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -95,6 +95,7 @@ struct iommu_domain { > void *handler_token; > struct iommu_domain_geometry geometry; > struct iommu_dma_cookie *iova_cookie; > + unsigned long concurrent_traversal:1;
Does this need to be a bitfield? Even though you are needing just one bit now, you can probably make have maskbits?
> }; > > static inline bool iommu_is_dma_domain(struct iommu_domain *domain) > @@ -657,6 +658,12 @@ static inline void dev_iommu_priv_set(struct device *dev, void *priv) > dev->iommu->priv = priv; > } > > +static inline void domain_set_concurrent_traversal(struct iommu_domain *domain, > + bool value) > +{ > + domain->concurrent_traversal = value; > +} > + > int iommu_probe_device(struct device *dev); > void iommu_release_device(struct device *dev); > > @@ -677,6 +684,8 @@ int iommu_group_claim_dma_owner(struct iommu_group *group, void *owner); > void iommu_group_release_dma_owner(struct iommu_group *group); > bool iommu_group_dma_owner_claimed(struct iommu_group *group); > > +void iommu_free_pgtbl_pages(struct iommu_domain *domain, > + struct list_head *pages); > #else /* CONFIG_IOMMU_API */ > > struct iommu_ops {}; > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 847ad47a2dfd..ceeb97ebe3e2 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -3252,3 +3252,26 @@ bool iommu_group_dma_owner_claimed(struct iommu_group *group) > return user; > } > EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed); > + > +static void pgtble_page_free_rcu(struct rcu_head *rcu)
maybe the names can be consistent? pgtble_ vs pgtbl below.
vote to drop the 'e' :-)
> +{ > + struct page *page = container_of(rcu, struct page, rcu_head); > + > + __free_pages(page, 0); > +} > + > +void iommu_free_pgtbl_pages(struct iommu_domain *domain, > + struct list_head *pages) > +{ > + struct page *page, *next; > + > + if (!domain->concurrent_traversal) { > + put_pages_list(pages); > + return; > + } > + > + list_for_each_entry_safe(page, next, pages, lru) { > + list_del(&page->lru); > + call_rcu(&page->rcu_head, pgtble_page_free_rcu); > + } > +} > -- > 2.25.1 >
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