powerpc/vphn: parsing code rewrite

The current VPHN parsing logic has some flaws that this patch aims to fix:

1) when the value 0xffff is read, the value 0xffffffff gets added to the
   the output list and its element count isn't incremented. This is wrong.
   According to PAPR+ the domain identifiers are packed into a sequence
   terminated by the "reserved value of all ones". This means that 0xffff
   is a stream terminator.

2) the combination of byteswaps and casts make the code hardly readable.
   Let's parse the stream one 16-bit field at a time instead.

3) it is assumed that the hypercall returns 12 32-bit values packed into
   6 64-bit registers. According to PAPR+, the domain identifiers may be
   streamed as 16-bit values. Let's increase the number of expected numbers
   to 24.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

2 files changed, 40 insertions, 20 deletions

diff --git a/arch/powerpc/mm/vphn.c b/arch/powerpc/mm/vphn.c
index c49ed519c381..5f8ef50e5c66 100644
--- a/arch/powerpc/mm/vphn.c
+++ b/arch/powerpc/mm/vphn.c
@@ -2,44 +2,64 @@
 #include "vphn.h"
 
 /*
- * Convert the associativity domain numbers returned from the hypervisor
- * to the sequence they would appear in the ibm,associativity property.
+ * The associativity domain numbers are returned from the hypervisor as a
+ * stream of mixed 16-bit and 32-bit fields. The stream is terminated by the
+ * special value of "all ones" (aka. 0xffff) and its size may not exceed 48
+ * bytes.
+ *
+ *    --- 16-bit fields -->
+ *  _________________________
+ *  |  0  |  1  |  2  |  3  |   be_packed[0]
+ *  ------+-----+-----+------
+ *  _________________________
+ *  |  4  |  5  |  6  |  7  |   be_packed[1]
+ *  -------------------------
+ *            ...
+ *  _________________________
+ *  | 20  | 21  | 22  | 23  |   be_packed[5]
+ *  -------------------------
+ *
+ * Convert to the sequence they would appear in the ibm,associativity property.
  */
 int vphn_unpack_associativity(const long *packed, __be32 *unpacked)
 {
         __be64 be_packed[VPHN_REGISTER_COUNT];
         int i, nr_assoc_doms = 0;
         const __be16 *field = (const __be16 *) be_packed;
+        u16 last = 0;
+        bool is_32bit = false;
 
 #define VPHN_FIELD_UNUSED       (0xffff)
 #define VPHN_FIELD_MSB          (0x8000)
 #define VPHN_FIELD_MASK         (~VPHN_FIELD_MSB)
 
-        /* Let's recreate the original stream. */
+        /* Let's fix the values returned by plpar_hcall9() */
         for (i = 0; i < VPHN_REGISTER_COUNT; i++)
                 be_packed[i] = cpu_to_be64(packed[i]);
 
         for (i = 1; i < VPHN_ASSOC_BUFSIZE; i++) {
-                if (be16_to_cpup(field) == VPHN_FIELD_UNUSED) {
-                        /* All significant fields processed, and remaining
-                         * fields contain the reserved value of all 1's.
-                         * Just store them.
+                u16 new = be16_to_cpup(field++);
+
+                if (is_32bit) {
+                        /* Let's concatenate the 16 bits of this field to the
+                         * 15 lower bits of the previous field
                          */
-                        unpacked[i] = *((__be32 *)field);
-                        field += 2;
-                } else if (be16_to_cpup(field) & VPHN_FIELD_MSB) {
+                        unpacked[++nr_assoc_doms] =
+                                cpu_to_be32(last << 16 | new);
+                        is_32bit = false;
+                } else if (new == VPHN_FIELD_UNUSED)
+                        /* This is the list terminator */
+                        break;
+                else if (new & VPHN_FIELD_MSB) {
                         /* Data is in the lower 15 bits of this field */
-                        unpacked[i] = cpu_to_be32(
-                                be16_to_cpup(field) & VPHN_FIELD_MASK);
-                        field++;
-                        nr_assoc_doms++;
+                        unpacked[++nr_assoc_doms] =
+                                cpu_to_be32(new & VPHN_FIELD_MASK);
                 } else {
                         /* Data is in the lower 15 bits of this field
                          * concatenated with the next 16 bit field
                          */
-                        unpacked[i] = *((__be32 *)field);
-                        field += 2;
-                        nr_assoc_doms++;
+                        last = new;
+                        is_32bit = true;
                 }
         }
 
diff --git a/arch/powerpc/mm/vphn.h b/arch/powerpc/mm/vphn.h
index 96af9a474693..fe8b7805b78f 100644
--- a/arch/powerpc/mm/vphn.h
+++ b/arch/powerpc/mm/vphn.h
@@ -6,10 +6,10 @@
 #define VPHN_REGISTER_COUNT 6
 
 /*
- * 6 64-bit registers unpacked into 12 32-bit associativity values. To form
- * the complete property we have to add the length in the first cell.
+ * 6 64-bit registers unpacked into up to 24 be32 associativity values. To
+ * form the complete property we have to add the length in the first cell.
  */
-#define VPHN_ASSOC_BUFSIZE (VPHN_REGISTER_COUNT*sizeof(u64)/sizeof(u32) + 1)
+#define VPHN_ASSOC_BUFSIZE (VPHN_REGISTER_COUNT*sizeof(u64)/sizeof(u16) + 1)
 
 extern int vphn_unpack_associativity(const long *packed, __be32 *unpacked);