Patchwork [36/48] mmu-hash*: Don't update PTE flags when permission is denied

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Submitter David Gibson
Date March 12, 2013, 10:31 a.m.
Message ID <1363084310-4115-37-git-send-email-david@gibson.dropbear.id.au>
Download mbox | patch
Permalink /patch/226914/
State New
Headers show

Comments

David Gibson - March 12, 2013, 10:31 a.m.
BEHAVIOUR CHANGE

Currently if ppc_hash{32,64}_translate() finds a PTE matching the given
virtual address, it will always update the PTE's R & C (Referenced and
Changed) bits.  This happens even if the PTE's permissions mean we are
about to deny the translation.

This is clearly a bug, although we get away with it because:
  a) It will only incorrectly set, never reset the bits, which should not
cause guest correctness problems.
  b) Linux guests never use the R & C bits anyway.

This patch fixes the behaviour, only updating R & C when access is granted
by the PTE.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 target-ppc/mmu-hash32.c |   12 +++++++-----
 target-ppc/mmu-hash64.c |   12 +++++++-----
 2 files changed, 14 insertions(+), 10 deletions(-)

Patch

diff --git a/target-ppc/mmu-hash32.c b/target-ppc/mmu-hash32.c
index 3488092..ae606fd 100644
--- a/target-ppc/mmu-hash32.c
+++ b/target-ppc/mmu-hash32.c
@@ -439,15 +439,17 @@  static int ppc_hash32_translate(CPUPPCState *env, struct mmu_ctx_hash32 *ctx,
     ctx->raddr = pte.pte1;
     ctx->prot = access;
     ret = ppc_hash32_check_prot(ctx->prot, rwx);
-    if (ret == 0) {
-        /* Access granted */
-        LOG_MMU("PTE access granted !\n");
-    } else {
+
+    if (ret) {
         /* Access right violation */
         LOG_MMU("PTE access rejected\n");
+        return ret;
     }
 
-    /* Update page flags */
+    LOG_MMU("PTE access granted !\n");
+
+    /* 8. Update PTE referenced and changed bits if necessary */
+
     if (ppc_hash32_pte_update_flags(ctx, &pte.pte1, ret, rwx) == 1) {
         ppc_hash32_store_hpte1(env, pte_offset, pte.pte1);
     }
diff --git a/target-ppc/mmu-hash64.c b/target-ppc/mmu-hash64.c
index 2e109f4..f7aa352 100644
--- a/target-ppc/mmu-hash64.c
+++ b/target-ppc/mmu-hash64.c
@@ -460,15 +460,17 @@  static int ppc_hash64_translate(CPUPPCState *env, struct mmu_ctx_hash64 *ctx,
     ctx->raddr = pte.pte1;
     ctx->prot = access;
     ret = ppc_hash64_check_prot(ctx->prot, rwx);
-    if (ret == 0) {
-        /* Access granted */
-        LOG_MMU("PTE access granted !\n");
-    } else {
+
+    if (ret) {
         /* Access right violation */
         LOG_MMU("PTE access rejected\n");
+        return ret;
     }
 
-    /* Update page flags */
+    LOG_MMU("PTE access granted !\n");
+
+    /* 6. Update PTE referenced and changed bits if necessary */
+
     if (ppc_hash64_pte_update_flags(ctx, &pte.pte1, ret, rwx) == 1) {
         ppc_hash64_store_hpte1(env, pte_offset, pte.pte1);
     }