x86_iommu/amd: remove V=1 check from amdvi_validate_dte()

Currently, the amdvi_validate_dte() assumes that a valid DTE will
always have V=1. This is not true. The V=1 means that bit[127:1] are
valid. A valid DTE can have IV=1 and V=0 (i.e address translation
disabled and interrupt remapping enabled)

Remove the V=1 check from amdvi_validate_dte(), make the caller
responsible to check for V or IV bits.

This also fixes a bug in existing code that when error is
detected during the translation we'll fail the translation
instead of assuming a passthrough mode.

Signed-off-by: Brijesh Singh <[email protected]>
Reviewed-by: Peter Xu <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Richard Henderson <[email protected]>
Cc: Eduardo Habkost <[email protected]>
Cc: Marcel Apfelbaum <[email protected]>
Cc: Tom Lendacky <[email protected]>
Cc: Suravee Suthikulpanit <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>

hw/i386/amd_iommu.c

@@ -807,7 +807,7 @@ static inline uint64_t amdvi_get_perms(uint64_t entry)
            AMDVI_DEV_PERM_SHIFT;
 }
 
-/* a valid entry should have V = 1 and reserved bits honoured */
+/* validate that reserved bits are honoured */
 static bool amdvi_validate_dte(AMDVIState *s, uint16_t devid,
                                uint64_t *dte)
 {
@@ -820,7 +820,7 @@ static bool amdvi_validate_dte(AMDVIState *s, uint16_t devid,
         return false;
     }
 
-    return dte[0] & AMDVI_DEV_VALID;
+    return true;
 }
 
 /* get a device table entry given the devid */
@@ -966,8 +966,12 @@ static void amdvi_do_translate(AMDVIAddressSpace *as, hwaddr addr,
         return;
     }
 
-    /* devices with V = 0 are not translated */
     if (!amdvi_get_dte(s, devid, entry)) {
+        return;
+    }
+
+    /* devices with V = 0 are not translated */
+    if (!(entry[0] & AMDVI_DEV_VALID)) {
         goto out;
     }