[v6,01/12] target/riscv: Update pmp_get_tlb_size()

Commit Message

Weiwei Li May 17, 2023, 9:15 a.m. UTC

PMP entries before (including) the matched PMP entry may only cover partial
of the TLB page, and this may split the page into regions with different
permissions. Such as for PMP0 (0x80000008~0x8000000F, R) and PMP1 (0x80000000~
0x80000FFF, RWX), write access to 0x80000000 will match PMP1. However we cannot
cache the translation result in the TLB since this will make the write access
to 0x80000008 bypass the check of PMP0. So we should check all of them instead
of the matched PMP entry in pmp_get_tlb_size() and set the tlb_size to 1 in
this case.
Set tlb_size to TARGET_PAGE_SIZE if PMP is not support or there is no PMP rules.

Signed-off-by: Weiwei Li <[e-mail]>
Signed-off-by: Junqiang Wang <[e-mail]>
Reviewed-by: LIU Zhiwei <[e-mail]>
Reviewed-by: Alistair Francis <[e-mail]>
---
 target/riscv/cpu_helper.c |  7 ++--
 target/riscv/pmp.c        | 69 ++++++++++++++++++++++++++++++---------
 target/riscv/pmp.h        |  3 +-
 3 files changed, 57 insertions(+), 22 deletions(-)

Patch

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 57d04385f1..de585b14cc 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -714,11 +714,8 @@  static int get_physical_address_pmp(CPURISCVState *env, int *prot,
     }
 
     *prot = pmp_priv_to_page_prot(pmp_priv);
-    if ((tlb_size != NULL) && pmp_index != MAX_RISCV_PMPS) {
-        target_ulong tlb_sa = addr & ~(TARGET_PAGE_SIZE - 1);
-        target_ulong tlb_ea = tlb_sa + TARGET_PAGE_SIZE - 1;
-
-        *tlb_size = pmp_get_tlb_size(env, pmp_index, tlb_sa, tlb_ea);
+    if (tlb_size != NULL) {
+        *tlb_size = pmp_get_tlb_size(env, addr);
     }
 
     return TRANSLATE_SUCCESS;
diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index 1f5aca42e8..406cff74f2 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -601,28 +601,67 @@  target_ulong mseccfg_csr_read(CPURISCVState *env)
 }
 
 /*
- * Calculate the TLB size if the start address or the end address of
- * PMP entry is presented in the TLB page.
+ * Calculate the TLB size.
+ * It's possible that PMP regions only cover partial of the TLB page, and
+ * this may split the page into regions with different permissions.
+ * For example if PMP0 is (0x80000008~0x8000000F, R) and PMP1 is (0x80000000
+ * ~0x80000FFF, RWX), then region 0x80000008~0x8000000F has R permission, and
+ * the other regions in this page have RWX permissions.
+ * A write access to 0x80000000 will match PMP1. However we cannot cache the
+ * translation result in the TLB since this will make the write access to
+ * 0x80000008 bypass the check of PMP0.
+ * To avoid this we return a size of 1 (which means no caching) if the PMP
+ * region only covers partial of the TLB page.
  */
-target_ulong pmp_get_tlb_size(CPURISCVState *env, int pmp_index,
-                              target_ulong tlb_sa, target_ulong tlb_ea)
+target_ulong pmp_get_tlb_size(CPURISCVState *env, target_ulong addr)
 {
-    target_ulong pmp_sa = env->pmp_state.addr[pmp_index].sa;
-    target_ulong pmp_ea = env->pmp_state.addr[pmp_index].ea;
+    target_ulong pmp_sa;
+    target_ulong pmp_ea;
+    target_ulong tlb_sa = addr & ~(TARGET_PAGE_SIZE - 1);
+    target_ulong tlb_ea = tlb_sa + TARGET_PAGE_SIZE - 1;
+    int i;
 
-    if (pmp_sa <= tlb_sa && pmp_ea >= tlb_ea) {
+    /*
+     * If PMP is not supported or there are no PMP rules, the TLB page will not
+     * be split into regions with different permissions by PMP so we set the
+     * size to TARGET_PAGE_SIZE.
+     */
+    if (!riscv_cpu_cfg(env)->pmp || !pmp_get_num_rules(env)) {
         return TARGET_PAGE_SIZE;
-    } else {
+    }
+
+    for (i = 0; i < MAX_RISCV_PMPS; i++) {
+        if (pmp_get_a_field(env->pmp_state.pmp[i].cfg_reg) == PMP_AMATCH_OFF) {
+            continue;
+        }
+
+        pmp_sa = env->pmp_state.addr[i].sa;
+        pmp_ea = env->pmp_state.addr[i].ea;
+
         /*
-         * At this point we have a tlb_size that is the smallest possible size
-         * That fits within a TARGET_PAGE_SIZE and the PMP region.
-         *
-         * If the size is less then TARGET_PAGE_SIZE we drop the size to 1.
-         * This means the result isn't cached in the TLB and is only used for
-         * a single translation.
+         * Only the first PMP entry that covers (whole or partial of) the TLB
+         * page really matters:
+         * If it covers the whole TLB page, set the size to TARGET_PAGE_SIZE,
+         * since the following PMP entries have lower priority and will not
+         * affect the permissions of the page.
+         * If it only covers partial of the TLB page, set the size to 1 since
+         * the allowed permissions of the region may be different from other
+         * region of the page.
          */
-        return 1;
+        if (pmp_sa <= tlb_sa && pmp_ea >= tlb_ea) {
+            return TARGET_PAGE_SIZE;
+        } else if ((pmp_sa >= tlb_sa && pmp_sa <= tlb_ea) ||
+                   (pmp_ea >= tlb_sa && pmp_ea <= tlb_ea)) {
+            return 1;
+        }
     }
+
+    /*
+     * If no PMP entry matches the TLB page, the TLB page will also not be
+     * split into regions with different permissions by PMP so we set the size
+     * to TARGET_PAGE_SIZE.
+     */
+    return TARGET_PAGE_SIZE;
 }
 
 /*
diff --git a/target/riscv/pmp.h b/target/riscv/pmp.h
index b296ea1fc6..0a7e24750b 100644
--- a/target/riscv/pmp.h
+++ b/target/riscv/pmp.h
@@ -76,8 +76,7 @@  int pmp_hart_has_privs(CPURISCVState *env, target_ulong addr,
                        target_ulong size, pmp_priv_t privs,
                        pmp_priv_t *allowed_privs,
                        target_ulong mode);
-target_ulong pmp_get_tlb_size(CPURISCVState *env, int pmp_index,
-                              target_ulong tlb_sa, target_ulong tlb_ea);
+target_ulong pmp_get_tlb_size(CPURISCVState *env, target_ulong addr);
 void pmp_update_rule_addr(CPURISCVState *env, uint32_t pmp_index);
 void pmp_update_rule_nums(CPURISCVState *env);
 uint32_t pmp_get_num_rules(CPURISCVState *env);