[Qemu-devel] [PATCH v2 2/4] intel_iommu: let iotlb size tunable

[Peter Xu <peterx@redhat.com>]

We were having static IOTLB size as 1024. Let it be a tunable. We can
also turns IOTLB off if we want, by specify the size as zero.

The tunable is named as "x-iotlb-size" since that should not really be
something used by user yet, but mostly for debugging purpose now.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 hw/i386/intel_iommu.c          | 11 ++++++++++-
 hw/i386/intel_iommu_internal.h |  1 -
 include/hw/i386/intel_iommu.h  |  1 +
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 392da45..9c36866 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -222,6 +222,10 @@ static VTDIOTLBEntry *vtd_lookup_iotlb(IntelIOMMUState *s, uint16_t source_id,
     uint64_t key;
     int level;
 
+    if (s->iotlb_size == 0) {
+        return NULL;
+    }
+
     for (level = VTD_SL_PT_LEVEL; level < VTD_SL_PML4_LEVEL; level++) {
         key = vtd_get_iotlb_key(vtd_get_iotlb_gfn(addr, level),
                                 source_id, level);
@@ -244,8 +248,12 @@ static void vtd_update_iotlb(IntelIOMMUState *s, uint16_t source_id,
     uint64_t *key = g_malloc(sizeof(*key));
     uint64_t gfn = vtd_get_iotlb_gfn(addr, level);
 
+    if (s->iotlb_size == 0) {
+        return;
+    }
+
     trace_vtd_iotlb_page_update(source_id, addr, slpte, domain_id);
-    if (g_hash_table_size(s->iotlb) >= VTD_IOTLB_MAX_SIZE) {
+    if (g_hash_table_size(s->iotlb) >= s->iotlb_size) {
         trace_vtd_iotlb_reset("iotlb exceeds size limit");
         vtd_reset_iotlb(s);
     }
@@ -2397,6 +2405,7 @@ static Property vtd_properties[] = {
                             ON_OFF_AUTO_AUTO),
     DEFINE_PROP_BOOL("x-buggy-eim", IntelIOMMUState, buggy_eim, false),
     DEFINE_PROP_BOOL("caching-mode", IntelIOMMUState, caching_mode, FALSE),
+    DEFINE_PROP_UINT16("x-iotlb-size", IntelIOMMUState, iotlb_size, 1024),
     DEFINE_PROP_END_OF_LIST(),
 };
 
diff --git a/hw/i386/intel_iommu_internal.h b/hw/i386/intel_iommu_internal.h
index d1d6290..dc0257c 100644
--- a/hw/i386/intel_iommu_internal.h
+++ b/hw/i386/intel_iommu_internal.h
@@ -116,7 +116,6 @@
 /* The shift of source_id in the key of IOTLB hash table */
 #define VTD_IOTLB_SID_SHIFT         36
 #define VTD_IOTLB_LVL_SHIFT         52
-#define VTD_IOTLB_MAX_SIZE          1024    /* Max size of the hash table */
 
 /* IOTLB_REG */
 #define VTD_TLB_GLOBAL_FLUSH        (1ULL << 60) /* Global invalidation */
diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
index 3e51876..a57f419 100644
--- a/include/hw/i386/intel_iommu.h
+++ b/include/hw/i386/intel_iommu.h
@@ -288,6 +288,7 @@ struct IntelIOMMUState {
 
     uint32_t context_cache_gen;     /* Should be in [1,MAX] */
     GHashTable *iotlb;              /* IOTLB */
+    uint16_t iotlb_size;            /* IOTLB max cache entries */
 
     MemoryRegionIOMMUOps iommu_ops;
     GHashTable *vtd_as_by_busptr;   /* VTDBus objects indexed by PCIBus* reference */
-- 
2.7.4