[XEN PATCH v4 2/5] AMD-Vi: Disable IOMMU if cx16 isn't supported

[Teddy Astie <teddy.astie@xxxxxxxxxx>]

All hardware with AMD-Vi has CMPXCHG16 support. Check this at initialisation
time, and remove the effectively-dead logic for the non-cx16 case.

Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx>
---
 xen/drivers/passthrough/amd/iommu_map.c     | 42 +++++++--------------
 xen/drivers/passthrough/amd/pci_amd_iommu.c |  6 +++
 2 files changed, 20 insertions(+), 28 deletions(-)

diff --git a/xen/drivers/passthrough/amd/iommu_map.c 
b/xen/drivers/passthrough/amd/iommu_map.c
index e0f4fe736a..f67975e700 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 +184,20 @@ 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..3a6a23f706 100644
--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -305,6 +305,12 @@ static int __init cf_check iov_detect(void)
     if ( !iommu_enable && !iommu_intremap )
         return 0;
 
+    if ( unlikely(!cpu_has_cx16) )
+    {
+        printk("AMD-Vi: CPU doesn't support CMPXCHG16B, disabling\n");
+        return -ENODEV;
+    }
+
     if ( (init_done ? amd_iommu_init_late()
                     : amd_iommu_init(false)) != 0 )
     {
-- 
2.44.0



Teddy Astie | Vates XCP-ng Intern

XCP-ng & Xen Orchestra - Vates solutions

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