From: Julien Grall <jgr...@amazon.com> The new x86 IOMMU page-tables allocator will release the pages when relinquishing the domain resources. However, this is not sufficient when the domain is dying because nothing prevents page-table to be allocated.
As the domain is dying, it is not necessary to continue to modify the IOMMU page-tables as they are going to be destroyed soon. At the moment, page-table allocates will only happen when iommu_map(). So after this change there will be no more page-table allocation happening. In order to observe d->is_dying correctly, we need to rely on per-arch locking, so the check to ignore IOMMU mapping is added on the per-driver map_page() callback. Signed-off-by: Julien Grall <jgr...@amazon.com> --- As discussed in v3, this is only covering 4.15. We can discuss post-4.15 how to catch page-table allocations if another caller (e.g. iommu_unmap() if we ever decide to support superpages) start to use the page-table allocator. Changes in v4: - Move the patch to the top of the queue - Reword the commit message Changes in v3: - Patch added. This is a replacement of "xen/iommu: iommu_map: Don't crash the domain if it is dying" --- xen/drivers/passthrough/amd/iommu_map.c | 12 ++++++++++++ xen/drivers/passthrough/vtd/iommu.c | 12 ++++++++++++ xen/drivers/passthrough/x86/iommu.c | 6 ++++++ 3 files changed, 30 insertions(+) diff --git a/xen/drivers/passthrough/amd/iommu_map.c b/xen/drivers/passthrough/amd/iommu_map.c index d3a8b1aec766..560af54b765b 100644 --- a/xen/drivers/passthrough/amd/iommu_map.c +++ b/xen/drivers/passthrough/amd/iommu_map.c @@ -285,6 +285,18 @@ int amd_iommu_map_page(struct domain *d, dfn_t dfn, mfn_t mfn, spin_lock(&hd->arch.mapping_lock); + /* + * IOMMU mapping request can be safely ignored when the domain is dying. + * + * hd->arch.mapping_lock guarantees that d->is_dying will be observed + * before any page tables are freed (see iommu_free_pgtables()). + */ + if ( d->is_dying ) + { + spin_unlock(&hd->arch.mapping_lock); + return 0; + } + rc = amd_iommu_alloc_root(d); if ( rc ) { diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c index d136fe36883b..b549a71530d5 100644 --- a/xen/drivers/passthrough/vtd/iommu.c +++ b/xen/drivers/passthrough/vtd/iommu.c @@ -1762,6 +1762,18 @@ static int __must_check intel_iommu_map_page(struct domain *d, dfn_t dfn, spin_lock(&hd->arch.mapping_lock); + /* + * IOMMU mapping request can be safely ignored when the domain is dying. + * + * hd->arch.mapping_lock guarantees that d->is_dying will be observed + * before any page tables are freed (see iommu_free_pgtables()) + */ + if ( d->is_dying ) + { + spin_unlock(&hd->arch.mapping_lock); + return 0; + } + pg_maddr = addr_to_dma_page_maddr(d, dfn_to_daddr(dfn), 1); if ( !pg_maddr ) { diff --git a/xen/drivers/passthrough/x86/iommu.c b/xen/drivers/passthrough/x86/iommu.c index cea1032b3d02..c6b03624fe28 100644 --- a/xen/drivers/passthrough/x86/iommu.c +++ b/xen/drivers/passthrough/x86/iommu.c @@ -267,6 +267,12 @@ int iommu_free_pgtables(struct domain *d) struct page_info *pg; unsigned int done = 0; + if ( !is_iommu_enabled(d) ) + return 0; + + /* After this barrier, no more IOMMU mapping can happen */ + spin_barrier(&hd->arch.mapping_lock); + while ( (pg = page_list_remove_head(&hd->arch.pgtables.list)) ) { free_domheap_page(pg); -- 2.17.1