[PATCH for-7.2] target/arm: Don't do two-stage lookup if stage 2 is disabled

[Peter Maydell]

In get_phys_addr_with_struct(), we call get_phys_addr_twostage() if
the CPU supports EL2.  However, we don't check here that stage 2 is
actually enabled.  Instead we only check that inside
get_phys_addr_twostage() to skip stage 2 translation.  This means
that even if stage 2 is disabled we still tell the stage 1 lookup to
do its page table walks via stage 2.

This works by luck for normal CPU accesses, but it breaks for debug
accesses, which are used by the disassembler and also by semihosting
file reads and writes, because the debug case takes a different code
path inside S1_ptw_translate().

This means that setups that use semihosting for file loads are broken
(a regression since 7.1, introduced in recent ptw refactoring), and
that sometimes disassembly in debug logs reports "unable to read
memory" rather than showing the guest insns.

Fix the bug by hoisting the "is stage 2 enabled?" check up to
get_phys_addr_with_struct(), so that we handle S2 disabled the same
way we do the "no EL2" case, with a simple single stage lookup.

Reported-by: Jens Wiklander <jens.wiklan...@linaro.org>
Reviewed-by: Richard Henderson <richard.hender...@linaro.org>
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
This patch has RTH's r-by because I ran a couple of options for
fixing this by him over private email.
---
 target/arm/ptw.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/target/arm/ptw.c b/target/arm/ptw.c
index 3745ac97234..4264002021a 100644
--- a/target/arm/ptw.c
+++ b/target/arm/ptw.c
@@ -2604,8 +2604,8 @@ static bool get_phys_addr_twostage(CPUARMState *env, 
S1Translate *ptw,
 
     ret = get_phys_addr_with_struct(env, ptw, address, access_type, result, 
fi);
 
-    /* If S1 fails or S2 is disabled, return early.  */
-    if (ret || regime_translation_disabled(env, ARMMMUIdx_Stage2, is_secure)) {
+    /* If S1 fails, return early.  */
+    if (ret) {
         return ret;
     }
 
@@ -2731,7 +2731,8 @@ static bool get_phys_addr_with_struct(CPUARMState *env, 
S1Translate *ptw,
          * Otherwise, a stage1+stage2 translation is just stage 1.
          */
         ptw->in_mmu_idx = mmu_idx = s1_mmu_idx;
-        if (arm_feature(env, ARM_FEATURE_EL2)) {
+        if (arm_feature(env, ARM_FEATURE_EL2) &&
+            !regime_translation_disabled(env, ARMMMUIdx_Stage2, is_secure)) {
             return get_phys_addr_twostage(env, ptw, address, access_type,
                                           result, fi);
         }
-- 
2.25.1