[PATCH v4] target/riscv: update checks on writing pmpcfg for Smepmp to version 1.0

[Alvin Chang]

Current checks on writing pmpcfg for Smepmp follows Smepmp version
0.9.1. However, Smepmp specification has already been ratified, and
there are some differences between version 0.9.1 and 1.0. In this
commit we update the checks of writing pmpcfg to follow Smepmp version
1.0.

When mseccfg.MML is set, the constraints to modify PMP rules are:
1. Locked rules cannot be removed or modified until a PMP reset, unless
   mseccfg.RLB is set.
2. From Smepmp specification version 1.0, chapter 2 section 4b:
   Adding a rule with executable privileges that either is M-mode-only
   or a locked Shared-Region is not possible and such pmpcfg writes are
   ignored, leaving pmpcfg unchanged.

The commit transfers the value of pmpcfg into the index of the Smepmp
truth table, and checks the rules by aforementioned specification
changes.

Signed-off-by: Alvin Chang <alvinga@andestech.com>
---
Changes from v3: Modify "epmp_operation" to "smepmp_operation".

Changes from v2: Adopt switch case ranges and numerical order.

Changes from v1: Convert ePMP over to Smepmp.

 target/riscv/pmp.c | 40 ++++++++++++++++++++++++++++++++--------
 1 file changed, 32 insertions(+), 8 deletions(-)

diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index a08cd95658..2ebf18c941 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -99,16 +99,40 @@ static void pmp_write_cfg(CPURISCVState *env, uint32_t 
pmp_index, uint8_t val)
                 locked = false;
             }
 
-            /* mseccfg.MML is set */
-            if (MSECCFG_MML_ISSET(env)) {
-                /* not adding execute bit */
-                if ((val & PMP_LOCK) != 0 && (val & PMP_EXEC) != PMP_EXEC) {
+            /*
+             * mseccfg.MML is set. Locked rules cannot be removed or modified
+             * until a PMP reset. Besides, from Smepmp specification version 
1.0
+             * , chapter 2 section 4b says:
+             * Adding a rule with executable privileges that either is
+             * M-mode-only or a locked Shared-Region is not possible and such
+             * pmpcfg writes are ignored, leaving pmpcfg unchanged.
+             */
+            if (MSECCFG_MML_ISSET(env) && !pmp_is_locked(env, pmp_index)) {
+                /*
+                 * Convert the PMP permissions to match the truth table in the
+                 * Smepmp spec.
+                 */
+                const uint8_t smepmp_operation =
+                    ((val & PMP_LOCK) >> 4) | ((val & PMP_READ) << 2) |
+                    (val & PMP_WRITE) | ((val & PMP_EXEC) >> 2);
+
+                switch (smepmp_operation) {
+                case 0 ... 8:
                     locked = false;
-                }
-                /* shared region and not adding X bit */
-                if ((val & PMP_LOCK) != PMP_LOCK &&
-                    (val & 0x7) != (PMP_WRITE | PMP_EXEC)) {
+                    break;
+                case 9 ... 11:
+                    break;
+                case 12:
+                    locked = false;
+                    break;
+                case 13:
+                    break;
+                case 14:
+                case 15:
                     locked = false;
+                    break;
+                default:
+                    g_assert_not_reached();
                 }
             }
         } else {
-- 
2.34.1