[Qemu-devel] [PATCH] intel-iommu: send PSI always when notify_unmap set

[Peter Xu <peterx@redhat.com>]

During IOVA page table walk, there is a special case when:

- notify_unmap is set, meanwhile
- entry is invalid

In the past, we skip the entry always.  This is not correct.  We should
send UNMAP notification to registered notifiers in this case.  Otherwise
some stall pages will still be mapped in the host even if L1 guest
unmapped them already.

Without this patch, nested device assignment to L2 guests might dump
some errors like:

qemu-system-x86_64: VFIO_MAP_DMA: -17
qemu-system-x86_64: vfio_dma_map(0x557305420c30, 0xad000, 0x1000,
                    0x7f89a920d000) = -17 (File exists)

To fix this, we need to apply this patch to L1 QEMU (L2 QEMU is not
affected by this problem).

Signed-off-by: Peter Xu <peterx@redhat.com>
---

To test nested assignment, one also needs to apply below patchset:
https://lkml.org/lkml/2018/4/18/5
---
 hw/i386/intel_iommu.c | 42 ++++++++++++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index fb31de9416..b359efd6f9 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -722,6 +722,15 @@ static int vtd_iova_to_slpte(VTDContextEntry *ce, uint64_t iova, bool is_write,
 
 typedef int (*vtd_page_walk_hook)(IOMMUTLBEntry *entry, void *private);
 
+static int vtd_page_walk_one(IOMMUTLBEntry *entry, int level,
+                             vtd_page_walk_hook hook_fn, void *private)
+{
+    assert(hook_fn);
+    trace_vtd_page_walk_one(level, entry->iova, entry->translated_addr,
+                            entry->addr_mask, entry->perm);
+    return hook_fn(entry, private);
+}
+
 /**
  * vtd_page_walk_level - walk over specific level for IOVA range
  *
@@ -781,28 +790,37 @@ static int vtd_page_walk_level(dma_addr_t addr, uint64_t start,
          */
         entry_valid = read_cur | write_cur;
 
+        entry.target_as = &address_space_memory;
+        entry.iova = iova & subpage_mask;
+        entry.perm = IOMMU_ACCESS_FLAG(read_cur, write_cur);
+        entry.addr_mask = ~subpage_mask;
+
         if (vtd_is_last_slpte(slpte, level)) {
-            entry.target_as = &address_space_memory;
-            entry.iova = iova & subpage_mask;
             /* NOTE: this is only meaningful if entry_valid == true */
             entry.translated_addr = vtd_get_slpte_addr(slpte, aw);
-            entry.addr_mask = ~subpage_mask;
-            entry.perm = IOMMU_ACCESS_FLAG(read_cur, write_cur);
             if (!entry_valid && !notify_unmap) {
                 trace_vtd_page_walk_skip_perm(iova, iova_next);
                 goto next;
             }
-            trace_vtd_page_walk_one(level, entry.iova, entry.translated_addr,
-                                    entry.addr_mask, entry.perm);
-            if (hook_fn) {
-                ret = hook_fn(&entry, private);
-                if (ret < 0) {
-                    return ret;
-                }
+            ret = vtd_page_walk_one(&entry, level, hook_fn, private);
+            if (ret < 0) {
+                return ret;
             }
         } else {
             if (!entry_valid) {
-                trace_vtd_page_walk_skip_perm(iova, iova_next);
+                if (notify_unmap) {
+                    /*
+                     * The whole entry is invalid; unmap it all.
+                     * Translated address is meaningless, zero it.
+                     */
+                    entry.translated_addr = 0x0;
+                    ret = vtd_page_walk_one(&entry, level, hook_fn, private);
+                    if (ret < 0) {
+                        return ret;
+                    }
+                } else {
+                    trace_vtd_page_walk_skip_perm(iova, iova_next);
+                }
                 goto next;
             }
             ret = vtd_page_walk_level(vtd_get_slpte_addr(slpte, aw), iova,
-- 
2.14.3