Take read and write from the s1perms.gcs bit computed
by the Arm pseudocode.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/ptw.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/target/arm/ptw.c b/target/arm/ptw.c
index 6c52ed1ad0..d4386ede73 100644
--- a/target/arm/ptw.c
+++ b/target/arm/ptw.c
@@ -1619,12 +1619,16 @@ static int get_S1prot_indirect(CPUARMState *env, S1Translate *ptw,
         }
     }
 
-    if (perm & PAGE_WXN) {
+    if (regime_is_gcs(mmu_idx)) {
+        /*
+         * Note that the one s1perms.gcs bit controls both read and write
+         * access via AccessType_GCS.  See AArch64.S1CheckPermissions.
+         */
+        perm = (perm & PAGE_GCS ? PAGE_READ | PAGE_WRITE : 0);
+    } else if (perm & PAGE_WXN) {
         perm &= ~PAGE_EXEC;
     }
 
-    /* TODO: FEAT_GCS */
-
     return perm & PAGE_RWX;
 }
 
@@ -2277,6 +2281,13 @@ static bool get_phys_addr_lpae(CPUARMState *env, S1Translate *ptw,
              */
             prot = get_S1prot_indirect(env, ptw, mmu_idx, pi, po,
                                        result->f.attrs.space, out_space);
+        } else if (regime_is_gcs(mmu_idx)) {
+            /*
+             * While one must use indirect permissions to successfully
+             * use GCS instructions, AArch64.S1DirectBasePermissions
+             * faithfully supplies s1perms.gcs = 0, Just In Case.
+             */
+            prot = 0;
         } else {
             int xn = extract64(attrs, 54, 1);
             int pxn = extract64(attrs, 53, 1);
-- 
2.43.0