Messages in this thread | | | Date | Fri, 10 Jun 2022 14:05:37 +0800 | Subject | Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support | From | Baolu Lu <> |
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On 2022/6/10 01:06, Raj, Ashok wrote: > 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
Above updated. Thank you!
>> >> 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? >
As discussed in another reply, I am about to drop the driver opt-in and wrapper the helper around the iommu_iotlb_gather.
> >> }; >> >> 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' :-)
Updated.
> >> +{ >> + 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 >>
Best regards, baolu
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