[XEN PATCH 2/3] AMD-Vi: Disable IOMMU if cx16 isn't supported

[Teddy Astie <teddy.astie@vates.tech>]

No hardware has VT-d support while not having cx16 support, consider disabling IOMMU in this case to avoid potentially buggy code.

Now that IOMMU is only enabled if cx16 is supported, drop dead code that handles cases where cx16 isn't supported.

Signed-off-by Teddy Astie <teddy.astie@vates.tech>
---
 xen/drivers/passthrough/amd/iommu_map.c     | 43 +++++++--------------
 xen/drivers/passthrough/amd/pci_amd_iommu.c |  6 +++
 2 files changed, 21 insertions(+), 28 deletions(-)

diff --git a/xen/drivers/passthrough/amd/iommu_map.c b/xen/drivers/passthrough/amd/iommu_map.c
index e0f4fe736a..c8c1c0cfae 100644
--- a/xen/drivers/passthrough/amd/iommu_map.c
+++ b/xen/drivers/passthrough/amd/iommu_map.c
@@ -167,15 +167,14 @@ int amd_iommu_set_root_page_table(struct amd_iommu_dte *dte,
 {
     bool valid = flags & SET_ROOT_VALID;
 
-    if ( dte->v && dte->tv &&
-         (cpu_has_cx16 || (flags & SET_ROOT_WITH_UNITY_MAP)) )
+    if ( dte->v && dte->tv )
     {
         union {
             struct amd_iommu_dte dte;
             uint64_t raw64[4];
             __uint128_t raw128[2];
         } ldte = { .dte = *dte };
-        __uint128_t old = ldte.raw128[0];
+        __uint128_t res, old = ldte.raw128[0];
         int ret = 0;
 
         ldte.dte.domain_id = domain_id;
@@ -185,33 +184,21 @@ int amd_iommu_set_root_page_table(struct amd_iommu_dte *dte,
         ldte.dte.paging_mode = paging_mode;
         ldte.dte.v = valid;
 
-        if ( cpu_has_cx16 )
-        {
-            __uint128_t res = cmpxchg16b(dte, &old, &ldte.raw128[0]);
+    
+        res = cmpxchg16b(dte, &old, &ldte.raw128[0]);
 
-            /*
-             * Hardware does not update the DTE behind our backs, so the
-             * return value should match "old".
-             */
-            if ( res != old )
-            {
-                printk(XENLOG_ERR
-                       "Dom%d: unexpected DTE %016lx_%016lx (expected %016lx_%016lx)\n",
-                       domain_id,
-                       (uint64_t)(res >> 64), (uint64_t)res,
-                       (uint64_t)(old >> 64), (uint64_t)old);
-                ret = -EILSEQ;
-            }
-        }
-        else /* Best effort, updating domain_id last. */
+        /*
+         * Hardware does not update the DTE behind our backs, so the
+         * return value should match "old".
+         */
+        if ( res != old )
         {
-            uint64_t *ptr = (void *)dte;
-
-            write_atomic(ptr + 0, ldte.raw64[0]);
-            /* No barrier should be needed between these two. */
-            write_atomic(ptr + 1, ldte.raw64[1]);
-
-            ret = 1;
+            printk(XENLOG_ERR
+                   "Dom%d: unexpected DTE %016lx_%016lx (expected %016lx_%016lx)\n",
+                   domain_id,
+                   (uint64_t)(res >> 64), (uint64_t)res,
+                   (uint64_t)(old >> 64), (uint64_t)old);
+            ret = -EILSEQ;
         }
 
         return ret;
diff --git a/xen/drivers/passthrough/amd/pci_amd_iommu.c b/xen/drivers/passthrough/amd/pci_amd_iommu.c
index f6efd88e36..656c5eda5d 100644
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -312,6 +312,12 @@ static int __init cf_check iov_detect(void)
         return -ENODEV;
     }
 
+    if ( unlikely(!cpu_has_cx16) )
+    {
+        printk("AMD-Vi: CPU doesn't support CMPXCHG16B, disabling\n");
+        return -ENOSYS;
+    }
+
     init_done = 1;
 
     if ( !amd_iommu_perdev_intremap )
-- 
2.44.0



Teddy Astie | Vates XCP-ng Intern

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech