[PATCH] target/arm: Do alignment check when translation disabled

[Richard Henderson <richard.henderson@linaro.org>]

If translation is disabled, the default memory type is Device,
which requires alignment checking.  Document, but defer, the
more general case of per-page alignment checking.

Reported-by: Idan Horowitz <idan.horowitz@gmail.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1204
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/helper.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index d7bc467a2a..79609443aa 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -10713,6 +10713,39 @@ ARMMMUIdx arm_mmu_idx(CPUARMState *env)
     return arm_mmu_idx_el(env, arm_current_el(env));
 }
 
+/*
+ * Return true if memory alignment should be enforced.
+ */
+static bool aprofile_require_alignment(CPUARMState *env, int el, uint64_t sctlr)
+{
+    /* Check the alignment enable bit. */
+    if (sctlr & SCTLR_A) {
+        return true;
+    }
+
+    /*
+     * If translation is disabled, then the default memory type
+     * may be Device(-nGnRnE) instead of Normal, which requires that
+     * alignment be enforced.
+     *
+     * TODO: The more general case is translation enabled, with a per-page
+     * check of the memory type as assigned via MAIR_ELx and the PTE.
+     * We could arrange for a bit in MemTxAttrs to enforce alignment
+     * via forced use of the softmmu slow path.  Given that such pages
+     * are intended for MMIO, where the slow path is required anyhow,
+     * this should not result in extra overhead.
+     */
+    if (sctlr & SCTLR_M) {
+        /* Translation enabled: memory type in PTE via MAIR_ELx. */
+        return false;
+    }
+    if (el < 2 && (arm_hcr_el2_eff(env) & (HCR_DC | HCR_VM))) {
+        /* Stage 2 translation enabled: memory type in PTE. */
+        return false;
+    }
+    return true;
+}
+
 static CPUARMTBFlags rebuild_hflags_common(CPUARMState *env, int fp_el,
                                            ARMMMUIdx mmu_idx,
                                            CPUARMTBFlags flags)
@@ -10777,8 +10810,9 @@ static CPUARMTBFlags rebuild_hflags_a32(CPUARMState *env, int fp_el,
 {
     CPUARMTBFlags flags = {};
     int el = arm_current_el(env);
+    uint64_t sctlr = arm_sctlr(env, el);
 
-    if (arm_sctlr(env, el) & SCTLR_A) {
+    if (aprofile_require_alignment(env, el, sctlr)) {
         DP_TBFLAG_ANY(flags, ALIGN_MEM, 1);
     }
 
@@ -10871,7 +10905,7 @@ static CPUARMTBFlags rebuild_hflags_a64(CPUARMState *env, int el, int fp_el,
 
     sctlr = regime_sctlr(env, stage1);
 
-    if (sctlr & SCTLR_A) {
+    if (aprofile_require_alignment(env, el, sctlr)) {
         DP_TBFLAG_ANY(flags, ALIGN_MEM, 1);
     }
 
-- 
2.34.1