[PATCH v2 4/4] intel_iommu: Optimize out some unnecessary UNMAP calls

[Zhenzhong Duan]

Commit 63b88968f1 ("intel-iommu: rework the page walk logic") adds IOVA
tree to cache mapped ranges so we only need to send MAP or UNMAP when
there are changes. But there is still a corner case of unnecessary UNMAP.

During invalidation, either domain or device selective, we only need to
unmap when there are recorded mapped IOVA ranges, presuming most of OSes
allocating IOVA range continuously, e.g. on x86, linux sets up mapping
from 0xffffffff downwards.

Strace shows UNMAP ioctl taking 0.000014us and we have 28 such ioctl()
in one invalidation, as two notifiers in x86 are split into power of 2
pieces.

ioctl(48, VFIO_IOMMU_UNMAP_DMA, 0x7ffffd5c42f0) = 0 <0.000014>

The other purpose of this patch is to eliminate noisy error log when we
work with IOMMUFD. It looks the duplicate UNMAP call will fail with IOMMUFD
while always succeed with legacy container. This behavior difference leads
to below error log for IOMMUFD:

IOMMU_IOAS_UNMAP failed: No such file or directory
vfio_container_dma_unmap(0x562012d6b6d0, 0x0, 0x80000000) = -2 (No such file or 
directory)
IOMMU_IOAS_UNMAP failed: No such file or directory
vfio_container_dma_unmap(0x562012d6b6d0, 0x80000000, 0x40000000) = -2 (No such 
file or directory)
...

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
---
 hw/i386/intel_iommu.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 061fcded0dfb..a5fd144aa246 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -3743,6 +3743,7 @@ static void vtd_address_space_unmap(VTDAddressSpace *as, 
IOMMUNotifier *n)
     hwaddr start = n->start;
     hwaddr end = n->end;
     IntelIOMMUState *s = as->iommu_state;
+    IOMMUTLBEvent event;
     DMAMap map;
 
     /*
@@ -3762,22 +3763,25 @@ static void vtd_address_space_unmap(VTDAddressSpace 
*as, IOMMUNotifier *n)
     assert(start <= end);
     size = remain = end - start + 1;
 
+    event.type = IOMMU_NOTIFIER_UNMAP;
+    event.entry.target_as = &address_space_memory;
+    event.entry.perm = IOMMU_NONE;
+    /* This field is meaningless for unmap */
+    event.entry.translated_addr = 0;
+
     while (remain >= VTD_PAGE_SIZE) {
-        IOMMUTLBEvent event;
         uint64_t mask = dma_aligned_pow2_mask(start, end, s->aw_bits);
         uint64_t size = mask + 1;
 
         assert(size);
 
-        event.type = IOMMU_NOTIFIER_UNMAP;
-        event.entry.iova = start;
-        event.entry.addr_mask = mask;
-        event.entry.target_as = &address_space_memory;
-        event.entry.perm = IOMMU_NONE;
-        /* This field is meaningless for unmap */
-        event.entry.translated_addr = 0;
-
-        memory_region_notify_iommu_one(n, &event);
+        map.iova = start;
+        map.size = mask;
+        if (iova_tree_find(as->iova_tree, &map)) {
+            event.entry.iova = start;
+            event.entry.addr_mask = mask;
+            memory_region_notify_iommu_one(n, &event);
+        }
 
         start += size;
         remain -= size;
@@ -3791,7 +3795,7 @@ static void vtd_address_space_unmap(VTDAddressSpace *as, 
IOMMUNotifier *n)
                              n->start, size);
 
     map.iova = n->start;
-    map.size = size;
+    map.size = size - 1; /* Inclusive */
     iova_tree_remove(as->iova_tree, map);
 }
 
-- 
2.34.1