amd_iommu: Toggle address translation mode on devtab entry invalidation

A guest must issue an INVALIDATE_DEVTAB_ENTRY command after changing a
Device Table entry (DTE) e.g. after attaching a device and setting up its
DTE. When intercepting this event, determine if the DTE has been configured
for paging or not, and toggle the appropriate memory regions to allow DMA
address translation for the address space if needed. Requires dma-remap=on.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250919213515.917111-19-alejandro.j.jimenez@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index ce5d4c36624fdc0f9311b3358581fc3718be872d..e916dcb2be381b2550dad6f969a92db05f03647b 100644 (file)
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -1032,18 +1032,136 @@ static void amdvi_reset_address_translation_all(AMDVIState *s)
     }
 }
 
+static void enable_dma_mode(AMDVIAddressSpace *as, bool inval_current)
+{
+    /*
+     * When enabling DMA mode for the purpose of isolating guest devices on
+     * a failure to retrieve or invalid DTE, all existing mappings must be
+     * dropped.
+     */
+    if (inval_current) {
+        IOMMUNotifier *n;
+        IOMMU_NOTIFIER_FOREACH(n, &as->iommu) {
+            amdvi_address_space_unmap(as, n);
+        }
+    }
+
+    if (as->addr_translation) {
+        return;
+    }
+
+    /* Installing DTE enabling translation, activate region */
+    as->addr_translation = true;
+    amdvi_switch_address_space(as);
+    /* Sync shadow page tables */
+    amdvi_address_space_sync(as);
+}
+
+/*
+ * If paging was previously in use in the address space
+ * - invalidate all existing mappings
+ * - switch to no_dma memory region
+ */
+static void enable_nodma_mode(AMDVIAddressSpace *as)
+{
+    IOMMUNotifier *n;
+
+    if (!as->addr_translation) {
+        /* passthrough is already active, nothing to do */
+        return;
+    }
+
+    as->addr_translation = false;
+    IOMMU_NOTIFIER_FOREACH(n, &as->iommu) {
+        /* Drop all mappings for the address space */
+        amdvi_address_space_unmap(as, n);
+    }
+    amdvi_switch_address_space(as);
+}
+
+/*
+ * A guest driver must issue the INVALIDATE_DEVTAB_ENTRY command to the IOMMU
+ * after changing a Device Table entry. We can use this fact to detect when a
+ * Device Table entry is created for a device attached to a paging domain and
+ * enable the corresponding IOMMU memory region to allow for DMA translation if
+ * appropriate.
+ */
+static void amdvi_update_addr_translation_mode(AMDVIState *s, uint16_t devid)
+{
+    uint8_t bus_num, devfn, dte_mode;
+    AMDVIAddressSpace *as;
+    uint64_t dte[4] = { 0 };
+    int ret;
+
+    /*
+     * Convert the devid encoded in the command to a bus and devfn in
+     * order to retrieve the corresponding address space.
+     */
+    bus_num = PCI_BUS_NUM(devid);
+    devfn = devid & 0xff;
+
+    /*
+     * The main buffer of size (AMDVIAddressSpace *) * (PCI_BUS_MAX) has already
+     * been allocated within AMDVIState, but must be careful to not access
+     * unallocated devfn.
+     */
+    if (!s->address_spaces[bus_num] || !s->address_spaces[bus_num][devfn]) {
+        return;
+    }
+    as = s->address_spaces[bus_num][devfn];
+
+    ret = amdvi_as_to_dte(as, dte);
+
+    if (!ret) {
+        dte_mode = (dte[0] >> AMDVI_DEV_MODE_RSHIFT) & AMDVI_DEV_MODE_MASK;
+    }
+
+    switch (ret) {
+    case 0:
+        /* DTE was successfully retrieved */
+        if (!dte_mode) {
+            enable_nodma_mode(as); /* DTE[V]=1 && DTE[Mode]=0 => passthrough */
+        } else {
+            enable_dma_mode(as, false); /* Enable DMA translation */
+        }
+        break;
+    case -AMDVI_FR_DTE_V:
+        /* DTE[V]=0, address is passed untranslated */
+        enable_nodma_mode(as);
+        break;
+    case -AMDVI_FR_DTE_RTR_ERR:
+    case -AMDVI_FR_DTE_TV:
+        /*
+         * Enforce isolation by using DMA in rare scenarios where the DTE cannot
+         * be retrieved or DTE[TV]=0. Existing mappings are dropped.
+         */
+        enable_dma_mode(as, true);
+        break;
+    }
+}
+
 /* log error without aborting since linux seems to be using reserved bits */
 static void amdvi_inval_devtab_entry(AMDVIState *s, uint64_t *cmd)
 {
     uint16_t devid = cpu_to_le16((uint16_t)extract64(cmd[0], 0, 16));
 
+    trace_amdvi_devtab_inval(PCI_BUS_NUM(devid), PCI_SLOT(devid),
+                             PCI_FUNC(devid));
+
     /* This command should invalidate internal caches of which there isn't */
     if (extract64(cmd[0], 16, 44) || cmd[1]) {
         amdvi_log_illegalcom_error(s, extract64(cmd[0], 60, 4),
                                    s->cmdbuf + s->cmdbuf_head);
+        return;
+    }
+
+    /*
+     * When DMA remapping capability is enabled, check if updated DTE is setup
+     * for paging or not, and configure the corresponding memory regions.
+     */
+    if (s->dma_remap) {
+        amdvi_update_addr_translation_mode(s, devid);
     }
-    trace_amdvi_devtab_inval(PCI_BUS_NUM(devid), PCI_SLOT(devid),
-                             PCI_FUNC(devid));
 }
 
 static void amdvi_complete_ppr(AMDVIState *s, uint64_t *cmd)