From: Jason Gunthorpe via iommu <iommu@lists.linux-foundation.org> To: Lu Baolu <baolu.lu@linux.intel.com> Cc: Kevin Tian <kevin.tian@intel.com>, Ashok Raj <ashok.raj@intel.com>, Robin Murphy <robin.murphy@arm.com>, linux-kernel@vger.kernel.org, Christoph Hellwig <hch@infradead.org>, iommu@lists.linux-foundation.org, Joao Martins <joao.m.martins@oracle.com>, Will Deacon <will@kernel.org> Subject: Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support Date: Thu, 9 Jun 2022 09:49:34 -0300 [thread overview] Message-ID: <20220609124934.GZ1343366@nvidia.com> (raw) In-Reply-To: <20220609070811.902868-1-baolu.lu@linux.intel.com> 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. > > 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. > > 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; > }; > > 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; > +} ?? If you want it to be a driver opt in I would just add a flags to the domain ops. "DOMAIN_FLAG_RCU_FREE_PAGES" > +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); > + } It seems OK, but I wonder if there is benifit to using put_pages_list() from the rcu callback Jason _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
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From: Jason Gunthorpe <jgg@nvidia.com> To: Lu Baolu <baolu.lu@linux.intel.com> Cc: Joerg Roedel <joro@8bytes.org>, Robin Murphy <robin.murphy@arm.com>, Kevin Tian <kevin.tian@intel.com>, Ashok Raj <ashok.raj@intel.com>, Christoph Hellwig <hch@infradead.org>, Will Deacon <will@kernel.org>, Joao Martins <joao.m.martins@oracle.com>, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCHES 1/2] iommu: Add RCU-protected page free support Date: Thu, 9 Jun 2022 09:49:34 -0300 [thread overview] Message-ID: <20220609124934.GZ1343366@nvidia.com> (raw) In-Reply-To: <20220609070811.902868-1-baolu.lu@linux.intel.com> 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. > > 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. > > 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; > }; > > 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; > +} ?? If you want it to be a driver opt in I would just add a flags to the domain ops. "DOMAIN_FLAG_RCU_FREE_PAGES" > +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); > + } It seems OK, but I wonder if there is benifit to using put_pages_list() from the rcu callback Jason
next prev parent reply other threads:[~2022-06-09 12:49 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-06-09 7:08 [RFC PATCHES 1/2] iommu: Add RCU-protected page free support Lu Baolu 2022-06-09 7:08 ` Lu Baolu 2022-06-09 7:08 ` [RFC PATCHES 2/2] iommu: Replace put_pages_list() with iommu_free_pgtbl_pages() Lu Baolu 2022-06-09 7:08 ` Lu Baolu 2022-06-09 12:49 ` Jason Gunthorpe via iommu [this message] 2022-06-09 12:49 ` [RFC PATCHES 1/2] iommu: Add RCU-protected page free support Jason Gunthorpe 2022-06-09 13:19 ` Robin Murphy 2022-06-09 13:19 ` Robin Murphy 2022-06-09 13:32 ` Jason Gunthorpe 2022-06-09 13:32 ` Jason Gunthorpe via iommu 2022-06-10 5:59 ` Baolu Lu 2022-06-10 5:59 ` Baolu Lu 2022-06-10 5:37 ` Baolu Lu 2022-06-10 5:37 ` Baolu Lu 2022-06-15 15:40 ` Jason Gunthorpe 2022-06-15 15:40 ` Jason Gunthorpe via iommu 2022-06-16 2:27 ` Baolu Lu 2022-06-16 2:27 ` Baolu Lu 2022-06-20 4:04 ` Jason Gunthorpe 2022-06-20 4:04 ` Jason Gunthorpe via iommu 2022-06-09 17:06 ` Raj, Ashok 2022-06-09 17:06 ` Raj, Ashok 2022-06-10 6:05 ` Baolu Lu 2022-06-10 6:05 ` Baolu Lu
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