commit e5e40999b5e03567ef654546e3d448431643f8f3
author Peter Maydell <peter.maydell@linaro.org> Tue Jun 26 17:50:41 2018 +0100
committer Peter Maydell <peter.maydell@linaro.org> Tue Jun 26 17:50:41 2018 +0100
tree 6a21df55ce3a5ee1f2cbf78e60c2f3840f21e2c7
parent 55df6fcf5476b44bc1b95554e686ab3e91d725c5

target/arm: Set page (region) size in get_phys_addr_pmsav7()

We want to handle small MPU region sizes for ARMv7M. To do this,
make get_phys_addr_pmsav7() set the page size to the region
size if it is less that TARGET_PAGE_SIZE, rather than working
only in TARGET_PAGE_SIZE chunks.

Since the core TCG code con't handle execution from small
MPU regions, we strip the exec permission from them so that
any execution attempts will cause an MPU exception, rather
than allowing it to end up with a cpu_abort() in
get_page_addr_code().

(The previous code's intention was to make any small page be
treated as having no permissions, but unfortunately errors
in the implementation meant that it didn't behave that way.
It's possible that some binaries using small regions were
accidentally working with our old behaviour and won't now.)

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20180620130619.11362-3-peter.maydell@linaro.org

target/arm/helper.c

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 1248d84..a7edeb6 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -9596,6 +9596,7 @@
 static bool get_phys_addr_pmsav7(CPUARMState *env, uint32_t address,
                                  MMUAccessType access_type, ARMMMUIdx mmu_idx,
                                  hwaddr *phys_ptr, int *prot,
+                                 target_ulong *page_size,
                                  ARMMMUFaultInfo *fi)
 {
     ARMCPU *cpu = arm_env_get_cpu(env);
@@ -9603,6 +9604,7 @@
     bool is_user = regime_is_user(env, mmu_idx);
 
     *phys_ptr = address;
+    *page_size = TARGET_PAGE_SIZE;
     *prot = 0;
 
     if (regime_translation_disabled(env, mmu_idx) ||
@@ -9675,16 +9677,12 @@
                     rsize++;
                 }
             }
-            if (rsize < TARGET_PAGE_BITS) {
-                qemu_log_mask(LOG_UNIMP,
-                              "DRSR[%d]: No support for MPU (sub)region size of"
-                              " %" PRIu32 " bytes. Minimum is %d.\n",
-                              n, (1 << rsize), TARGET_PAGE_SIZE);
-                continue;
-            }
             if (srdis) {
                 continue;
             }
+            if (rsize < TARGET_PAGE_BITS) {
+                *page_size = 1 << rsize;
+            }
             break;
         }
 
@@ -9765,6 +9763,17 @@
 
     fi->type = ARMFault_Permission;
     fi->level = 1;
+    /*
+     * Core QEMU code can't handle execution from small pages yet, so
+     * don't try it. This way we'll get an MPU exception, rather than
+     * eventually causing QEMU to exit in get_page_addr_code().
+     */
+    if (*page_size < TARGET_PAGE_SIZE && (*prot & PAGE_EXEC)) {
+        qemu_log_mask(LOG_UNIMP,
+                      "MPU: No support for execution from regions "
+                      "smaller than 1K\n");
+        *prot &= ~PAGE_EXEC;
+    }
     return !(*prot & (1 << access_type));
 }
 
@@ -10334,7 +10343,7 @@
         } else if (arm_feature(env, ARM_FEATURE_V7)) {
             /* PMSAv7 */
             ret = get_phys_addr_pmsav7(env, address, access_type, mmu_idx,
-                                       phys_ptr, prot, fi);
+                                       phys_ptr, prot, page_size, fi);
         } else {
             /* Pre-v7 MPU */
             ret = get_phys_addr_pmsav5(env, address, access_type, mmu_idx,
@@ -10396,9 +10405,15 @@
                         core_to_arm_mmu_idx(env, mmu_idx), &phys_addr,
                         &attrs, &prot, &page_size, fi, NULL);
     if (!ret) {
-        /* Map a single [sub]page.  */
-        phys_addr &= TARGET_PAGE_MASK;
-        address &= TARGET_PAGE_MASK;
+        /*
+         * Map a single [sub]page. Regions smaller than our declared
+         * target page size are handled specially, so for those we
+         * pass in the exact addresses.
+         */
+        if (page_size >= TARGET_PAGE_SIZE) {
+            phys_addr &= TARGET_PAGE_MASK;
+            address &= TARGET_PAGE_MASK;
+        }
         tlb_set_page_with_attrs(cs, address, phys_addr, attrs,
                                 prot, mmu_idx, page_size);
         return 0;