[v3,20/20] target/arm: Fix alignment fault priority in get_phys_addr_lpae

Commit Message

Richard Henderson Oct. 9, 2024, 12:04 a.m. UTC

Now that we have the MemOp for the access, we can order
the alignment fault caused by memory type before the
permission fault for the page.

For subsequent page hits, permission and stage 2 checks
are known to pass, and so the TLB_CHECK_ALIGNED fault
raised in generic code is not mis-ordered.

Reviewed-by: Peter Maydell <[e-mail]>
Signed-off-by: Richard Henderson <[e-mail]>
---
 target/arm/ptw.c | 51 ++++++++++++++++++++++++++++--------------------
 1 file changed, 30 insertions(+), 21 deletions(-)

Patch

diff --git a/target/arm/ptw.c b/target/arm/ptw.c
index 0a1a820362..dd40268397 100644
--- a/target/arm/ptw.c
+++ b/target/arm/ptw.c
@@ -2129,6 +2129,36 @@  static bool get_phys_addr_lpae(CPUARMState *env, S1Translate *ptw,
         device = S1_attrs_are_device(result->cacheattrs.attrs);
     }
 
+    /*
+     * Enable alignment checks on Device memory.
+     *
+     * Per R_XCHFJ, the correct ordering for alignment, permission,
+     * and stage 2 faults is:
+     *    - Alignment fault caused by the memory type
+     *    - Permission fault
+     *    - A stage 2 fault on the memory access
+     * Perform the alignment check now, so that we recognize it in
+     * the correct order.  Set TLB_CHECK_ALIGNED so that any subsequent
+     * softmmu tlb hit will also check the alignment; clear along the
+     * non-device path so that tlb_fill_flags is consistent in the
+     * event of restart_atomic_update.
+     *
+     * In v7, for a CPU without the Virtualization Extensions this
+     * access is UNPREDICTABLE; we choose to make it take the alignment
+     * fault as is required for a v7VE CPU. (QEMU doesn't emulate any
+     * CPUs with ARM_FEATURE_LPAE but not ARM_FEATURE_V7VE anyway.)
+     */
+    if (device) {
+        unsigned a_bits = memop_atomicity_bits(memop);
+        if (address & ((1 << a_bits) - 1)) {
+            fi->type = ARMFault_Alignment;
+            goto do_fault;
+        }
+        result->f.tlb_fill_flags = TLB_CHECK_ALIGNED;
+    } else {
+        result->f.tlb_fill_flags = 0;
+    }
+
     if (!(result->f.prot & (1 << access_type))) {
         fi->type = ARMFault_Permission;
         goto do_fault;
@@ -2156,27 +2186,6 @@  static bool get_phys_addr_lpae(CPUARMState *env, S1Translate *ptw,
     result->f.attrs.space = out_space;
     result->f.attrs.secure = arm_space_is_secure(out_space);
 
-    /*
-     * Enable alignment checks on Device memory.
-     *
-     * Per R_XCHFJ, this check is mis-ordered. The correct ordering
-     * for alignment, permission, and stage 2 faults should be:
-     *    - Alignment fault caused by the memory type
-     *    - Permission fault
-     *    - A stage 2 fault on the memory access
-     * but due to the way the TCG softmmu TLB operates, we will have
-     * implicitly done the permission check and the stage2 lookup in
-     * finding the TLB entry, so the alignment check cannot be done sooner.
-     *
-     * In v7, for a CPU without the Virtualization Extensions this
-     * access is UNPREDICTABLE; we choose to make it take the alignment
-     * fault as is required for a v7VE CPU. (QEMU doesn't emulate any
-     * CPUs with ARM_FEATURE_LPAE but not ARM_FEATURE_V7VE anyway.)
-     */
-    if (device) {
-        result->f.tlb_fill_flags |= TLB_CHECK_ALIGNED;
-    }
-
     /*
      * For FEAT_LPA2 and effective DS, the SH field in the attributes
      * was re-purposed for output address bits.  The SH attribute in