[PATCH v3 3/3] target/ppc: Check page dir/table base alignment

[Leandro Lupori]

According to PowerISA 3.1B, Book III 6.7.6 programming note, the
page directory base addresses are expected to be aligned to their
size. Real hardware seems to rely on that and will access the
wrong address if they are misaligned. This results in a
translation failure even if the page tables seem to be properly
populated.

Signed-off-by: Leandro Lupori <leandro.lupori@eldorado.org.br>
---
 target/ppc/mmu-radix64.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/target/ppc/mmu-radix64.c b/target/ppc/mmu-radix64.c
index 705bff76be..00f2e9fa2e 100644
--- a/target/ppc/mmu-radix64.c
+++ b/target/ppc/mmu-radix64.c
@@ -265,7 +265,7 @@ static int ppc_radix64_next_level(AddressSpace *as, vaddr 
eaddr,
                                   uint64_t *pte_addr, uint64_t *nls,
                                   int *psize, uint64_t *pte, int *fault_cause)
 {
-    uint64_t index, pde;
+    uint64_t index, mask, nlb, pde;
 
     /* Read page <directory/table> entry from guest address space */
     pde = ldq_phys(as, *pte_addr);
@@ -280,7 +280,17 @@ static int ppc_radix64_next_level(AddressSpace *as, vaddr 
eaddr,
         *nls = pde & R_PDE_NLS;
         index = eaddr >> (*psize - *nls);       /* Shift */
         index &= ((1UL << *nls) - 1);           /* Mask */
-        *pte_addr = (pde & R_PDE_NLB) + (index * sizeof(pde));
+        nlb = pde & R_PDE_NLB;
+        mask = MAKE_64BIT_MASK(0, *nls + 3);
+
+        if (nlb & mask) {
+            qemu_log_mask(LOG_GUEST_ERROR,
+                "%s: misaligned page dir/table base: 0x"TARGET_FMT_lx
+                " page dir size: 0x"TARGET_FMT_lx"\n",
+                __func__, nlb, mask + 1);
+            nlb &= ~mask;
+        }
+        *pte_addr = nlb + index * sizeof(pde);
     }
     return 0;
 }
@@ -294,8 +304,18 @@ static int ppc_radix64_walk_tree(AddressSpace *as, vaddr 
eaddr,
     int level = 0;
 
     index = eaddr >> (*psize - nls);    /* Shift */
-    index &= ((1UL << nls) - 1);       /* Mask */
-    *pte_addr = base_addr + (index * sizeof(pde));
+    index &= ((1UL << nls) - 1);        /* Mask */
+    mask = MAKE_64BIT_MASK(0, nls + 3);
+
+    if (base_addr & mask) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+            "%s: misaligned page dir base: 0x"TARGET_FMT_lx
+            " page dir size: 0x"TARGET_FMT_lx"\n",
+            __func__, base_addr, mask + 1);
+        base_addr &= ~mask;
+    }
+    *pte_addr = base_addr + index * sizeof(pde);
+
     do {
         int ret;
 
-- 
2.25.1