[xen staging] xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying

[patchbot@xxxxxxx]

commit 1ef48c82e77692f63114cb6bdeee8a9261dbe493
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Fri Feb 26 10:56:39 2021 +0000
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Tue Mar 2 09:52:30 2021 +0000

    xen/x86: iommu: Ignore IOMMU mapping requests when a domain is dying
    
    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 because we don't use superpage mappings yet when not sharing
    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.
    
    Fixes: 15bc9a1ef51c ("x86/iommu: add common page-table allocator")
    Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
 xen/drivers/passthrough/amd/iommu_map.c | 12 ++++++++++++
 xen/drivers/passthrough/vtd/iommu.c     | 12 ++++++++++++
 xen/drivers/passthrough/x86/iommu.c     |  3 +++
 3 files changed, 27 insertions(+)

diff --git a/xen/drivers/passthrough/amd/iommu_map.c 
b/xen/drivers/passthrough/amd/iommu_map.c
index d3a8b1aec7..560af54b76 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 d136fe3688..b549a71530 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 58a330e822..ad19b7dd46 100644
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -270,6 +270,9 @@ int iommu_free_pgtables(struct domain *d)
     if ( !is_iommu_enabled(d) )
         return 0;
 
+    /* After this barrier, no new IOMMU mappings can be inserted. */
+    spin_barrier(&hd->arch.mapping_lock);
+
     while ( (pg = page_list_remove_head(&hd->arch.pgtables.list)) )
     {
         free_domheap_page(pg);
--
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