[PATCH v3 2/7] dma: Introduce dma_aligned_pow2_mask()

[Eric Auger]

Currently get_naturally_aligned_size() is used by the intel iommu
to compute the maximum invalidation range based on @size which is
a power of 2 while being aligned with the @start address and less
than the maximum range defined by @gaw.

This helper is also useful for other iommu devices (virtio-iommu,
SMMUv3) to make sure IOMMU UNMAP notifiers only are called with
power of 2 range sizes.

Let's move this latter into dma-helpers.c and rename it into
dma_aligned_pow2_mask(). Also rewrite the helper so that it
accomodates UINT64_MAX values for the size mask and max mask.
It now returns a mask instead of a size. Change the caller.

Signed-off-by: Eric Auger <eric.auger@redhat.com>

---

v2 -> v3:
- Added doc-comment as suggested by Peter Xu and Peter Maydell
---
 hw/i386/intel_iommu.c | 30 +++++++-----------------------
 include/sysemu/dma.h  | 12 ++++++++++++
 softmmu/dma-helpers.c | 26 ++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 23 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 3206f379f8..6be8f32918 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -35,6 +35,7 @@
 #include "hw/i386/x86-iommu.h"
 #include "hw/pci-host/q35.h"
 #include "sysemu/kvm.h"
+#include "sysemu/dma.h"
 #include "sysemu/sysemu.h"
 #include "hw/i386/apic_internal.h"
 #include "kvm/kvm_i386.h"
@@ -3455,24 +3456,6 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, 
PCIBus *bus, int devfn)
     return vtd_dev_as;
 }
 
-static uint64_t get_naturally_aligned_size(uint64_t start,
-                                           uint64_t size, int gaw)
-{
-    uint64_t max_mask = 1ULL << gaw;
-    uint64_t alignment = start ? start & -start : max_mask;
-
-    alignment = MIN(alignment, max_mask);
-    size = MIN(size, max_mask);
-
-    if (alignment <= size) {
-        /* Increase the alignment of start */
-        return alignment;
-    } else {
-        /* Find the largest page mask from size */
-        return 1ULL << (63 - clz64(size));
-    }
-}
-
 /* Unmap the whole range in the notifier's scope. */
 static void vtd_address_space_unmap(VTDAddressSpace *as, IOMMUNotifier *n)
 {
@@ -3501,13 +3484,14 @@ static void vtd_address_space_unmap(VTDAddressSpace 
*as, IOMMUNotifier *n)
 
     while (remain >= VTD_PAGE_SIZE) {
         IOMMUTLBEvent event;
-        uint64_t mask = get_naturally_aligned_size(start, remain, s->aw_bits);
+        uint64_t mask = dma_aligned_pow2_mask(start, end, s->aw_bits);
+        uint64_t size = mask + 1;
 
-        assert(mask);
+        assert(size);
 
         event.type = IOMMU_NOTIFIER_UNMAP;
         event.entry.iova = start;
-        event.entry.addr_mask = mask - 1;
+        event.entry.addr_mask = mask;
         event.entry.target_as = &address_space_memory;
         event.entry.perm = IOMMU_NONE;
         /* This field is meaningless for unmap */
@@ -3515,8 +3499,8 @@ static void vtd_address_space_unmap(VTDAddressSpace *as, 
IOMMUNotifier *n)
 
         memory_region_notify_iommu_one(n, &event);
 
-        start += mask;
-        remain -= mask;
+        start += size;
+        remain -= size;
     }
 
     assert(!remain);
diff --git a/include/sysemu/dma.h b/include/sysemu/dma.h
index a052f7bca3..3201e7901d 100644
--- a/include/sysemu/dma.h
+++ b/include/sysemu/dma.h
@@ -296,4 +296,16 @@ uint64_t dma_buf_write(uint8_t *ptr, int32_t len, 
QEMUSGList *sg);
 void dma_acct_start(BlockBackend *blk, BlockAcctCookie *cookie,
                     QEMUSGList *sg, enum BlockAcctType type);
 
+/**
+ * dma_aligned_pow2_mask: Return the address bit mask of the largest
+ * power of 2 size less or equal than @end - @start + 1, aligned with @start,
+ * and bounded by 1 << @max_addr_bits bits.
+ *
+ * @start: range start address
+ * @end: range end address (greater than @start)
+ * @max_addr_bits: max address bits (<= 64)
+ */
+uint64_t dma_aligned_pow2_mask(uint64_t start, uint64_t end,
+                               int max_addr_bits);
+
 #endif
diff --git a/softmmu/dma-helpers.c b/softmmu/dma-helpers.c
index 29001b5459..7d766a5e89 100644
--- a/softmmu/dma-helpers.c
+++ b/softmmu/dma-helpers.c
@@ -330,3 +330,29 @@ void dma_acct_start(BlockBackend *blk, BlockAcctCookie 
*cookie,
 {
     block_acct_start(blk_get_stats(blk), cookie, sg->size, type);
 }
+
+uint64_t dma_aligned_pow2_mask(uint64_t start, uint64_t end, int max_addr_bits)
+{
+    uint64_t max_mask = UINT64_MAX, addr_mask = end - start;
+    uint64_t alignment_mask, size_mask;
+
+    if (max_addr_bits != 64) {
+        max_mask = (1ULL << max_addr_bits) - 1;
+    }
+
+    alignment_mask = start ? (start & -start) - 1 : max_mask;
+    alignment_mask = MIN(alignment_mask, max_mask);
+    size_mask = MIN(addr_mask, max_mask);
+
+    if (alignment_mask <= size_mask) {
+        /* Increase the alignment of start */
+        return alignment_mask;
+    } else {
+        /* Find the largest page mask from size */
+        if (addr_mask == UINT64_MAX) {
+            return UINT64_MAX;
+        }
+        return (1ULL << (63 - clz64(addr_mask + 1))) - 1;
+    }
+}
+
-- 
2.26.2