[for-4.15][PATCH v3 2/3] xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying

[Julien Grall <julien@xen.org>]

From: Julien Grall <jgrall@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.

Currently page-table allocations can only happen from iommu_map(). As
the domain is dying, there is no good reason to continue to modify the
IOMMU page-tables.

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 <jgrall@amazon.com>

---

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 | 13 +++++++++++++
 xen/drivers/passthrough/vtd/iommu.c     | 13 +++++++++++++
 xen/drivers/passthrough/x86/iommu.c     |  3 +++
 3 files changed, 29 insertions(+)

diff --git a/xen/drivers/passthrough/amd/iommu_map.c b/xen/drivers/passthrough/amd/iommu_map.c
index d3a8b1aec766..ed78a083ba12 100644
--- a/xen/drivers/passthrough/amd/iommu_map.c
+++ b/xen/drivers/passthrough/amd/iommu_map.c
@@ -285,6 +285,19 @@ 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() and
+     * iommu_clear_root_pgtable()).
+     */
+    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 e1871f6c2bc1..239a63f74f64 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -1771,6 +1771,19 @@ 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() and
+     * iommu_clear_root_pgtable()).
+     */
+    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 f54fc8093f18..faa0078db595 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -273,6 +273,9 @@ int iommu_free_pgtables(struct domain *d)
     /*
      * Pages will be moved to the free list below. So we want to
      * clear the root page-table to avoid any potential use after-free.
+     *
+     * After this call, no more IOMMU mapping can happen.
+     *
      */
     hd->platform_ops->clear_root_pgtable(d);
 
-- 
2.17.1