[PATCH v9 3/8] iommu: flush I/O TLB if iommu_map() or iommu_unmap() fail

[Paul Durrant <paul@xen.org>]

From: Paul Durrant <pdurrant@amazon.com>

This patch adds a full I/O TLB flush to the error paths of iommu_map() and
iommu_unmap().

Without this change callers need constructs such as:

rc = iommu_map/unmap(...)
err = iommu_flush(...)
if ( !rc )
  rc = err;

With this change, it can be simplified to:

rc = iommu_map/unmap(...)
if ( !rc )
  rc = iommu_flush(...)

because, if the map or unmap fails the flush will be unnecessary. This saves
a stack variable and generally makes the call sites tidier.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---

v6:
 - Remove stray blank

v5:
 - Avoid unnecessary flushing if 'page_order' is 0
 - Add missing indirection on 'flush_flags'

v2:
 - New in v2
---
 xen/drivers/passthrough/iommu.c | 34 +++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index 660dc5deb2..eb65631d59 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -274,6 +274,13 @@ int iommu_map(struct domain *d, dfn_t dfn, mfn_t mfn,
         break;
     }
 
+    /*
+     * Something went wrong so, if we were dealing with more than a single
+     * page, flush everything and clear flush flags.
+     */
+    if ( page_order && unlikely(rc) && !iommu_iotlb_flush_all(d, *flush_flags) )
+        *flush_flags = 0;
+
     return rc;
 }
 
@@ -283,14 +290,8 @@ int iommu_legacy_map(struct domain *d, dfn_t dfn, mfn_t mfn,
     unsigned int flush_flags = 0;
     int rc = iommu_map(d, dfn, mfn, page_order, flags, &flush_flags);
 
-    if ( !this_cpu(iommu_dont_flush_iotlb) )
-    {
-        int err = iommu_iotlb_flush(d, dfn, (1u << page_order),
-                                    flush_flags);
-
-        if ( !rc )
-            rc = err;
-    }
+    if ( !this_cpu(iommu_dont_flush_iotlb) && !rc )
+        rc = iommu_iotlb_flush(d, dfn, (1u << page_order), flush_flags);
 
     return rc;
 }
@@ -330,6 +331,13 @@ int iommu_unmap(struct domain *d, dfn_t dfn, unsigned int page_order,
         }
     }
 
+    /*
+     * Something went wrong so, if we were dealing with more than a single
+     * page, flush everything and clear flush flags.
+     */
+    if ( page_order && unlikely(rc) && !iommu_iotlb_flush_all(d, *flush_flags) )
+        *flush_flags = 0;
+
     return rc;
 }
 
@@ -338,14 +346,8 @@ int iommu_legacy_unmap(struct domain *d, dfn_t dfn, unsigned int page_order)
     unsigned int flush_flags = 0;
     int rc = iommu_unmap(d, dfn, page_order, &flush_flags);
 
-    if ( !this_cpu(iommu_dont_flush_iotlb) )
-    {
-        int err = iommu_iotlb_flush(d, dfn, (1u << page_order),
-                                    flush_flags);
-
-        if ( !rc )
-            rc = err;
-    }
+    if ( !this_cpu(iommu_dont_flush_iotlb) && !rc )
+        rc = iommu_iotlb_flush(d, dfn, (1u << page_order), flush_flags);
 
     return rc;
 }
-- 
2.20.1