amd_iommu: Helper to decode size of page invalidation command

The size of the region to invalidate depends on the S bit and address
encoded in the command. Add a helper to extract this information, which
will be used to sync shadow page tables in upcoming changes.

Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <20250919213515.917111-5-alejandro.j.jimenez@oracle.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

2 files changed, 38 insertions, 0 deletions

diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index 3cbc9499db..202f0f8c6e 100644
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -577,6 +577,40 @@ static gboolean amdvi_iotlb_remove_by_domid(gpointer key, gpointer value,
     return entry->domid == domid;
 }
 
+/*
+ * Helper to decode the size of the range to invalidate encoded in the
+ * INVALIDATE_IOMMU_PAGES Command format.
+ * The size of the region to invalidate depends on the S bit and address.
+ * S bit value:
+ * 0 :  Invalidation size is 4 Kbytes.
+ * 1 :  Invalidation size is determined by first zero bit in the address
+ *      starting from Address[12].
+ *
+ * In the AMD IOMMU Linux driver, an invalidation command with address
+ * ((1 << 63) - 1) is sent when intending to clear the entire cache.
+ * However, Table 14: Example Page Size Encodings shows that an address of
+ * ((1ULL << 51) - 1) encodes the entire cache, so effectively any address with
+ * first zero at bit 51 or larger is a request to invalidate the entire address
+ * space.
+ */
+static uint64_t __attribute__((unused))
+amdvi_decode_invalidation_size(hwaddr addr, uint16_t flags)
+{
+    uint64_t size = AMDVI_PAGE_SIZE;
+    uint8_t fzbit = 0;
+
+    if (flags & AMDVI_CMD_INVAL_IOMMU_PAGES_S) {
+        fzbit = cto64(addr | 0xFFF);
+
+        if (fzbit >= 51) {
+            size = AMDVI_INV_ALL_PAGES;
+        } else {
+            size = 1ULL << (fzbit + 1);
+        }
+    }
+    return size;
+}
+
 /* we don't have devid - we can't remove pages by address */
 static void amdvi_inval_pages(AMDVIState *s, uint64_t *cmd)
 {
diff --git a/hw/i386/amd_iommu.h b/hw/i386/amd_iommu.h
index 2476296c49..c1170a8202 100644
--- a/hw/i386/amd_iommu.h
+++ b/hw/i386/amd_iommu.h
@@ -126,6 +126,10 @@
 #define AMDVI_CMD_COMPLETE_PPR_REQUEST    0x07
 #define AMDVI_CMD_INVAL_AMDVI_ALL         0x08
 
+
+#define AMDVI_CMD_INVAL_IOMMU_PAGES_S   (1ULL << 0)
+#define AMDVI_INV_ALL_PAGES             (1ULL << 52)
+
 #define AMDVI_DEVTAB_ENTRY_SIZE           32
 
 /* Device table entry bits 0:63 */