sel4utils: properly cache ept pages (#43)

A kernel bug previously always cached EPT page regardless of the cacheable flag. When the bug was fixed, this function would always map EPT pages as uncacheable, due to the attributes difference between an EPT map and a normal page map. This commit checks if the function is mapping an EPT and provides the proper cache attribute to the kernel. Signed-off-by: Chris Guikema <[email protected]>
seL4 · Sep 6, 2021 · dd02025 · dd02025
1 parent 6de2249
commit dd02025
Showing 1 changed file with 13 additions and 0 deletions.
diff --git a/libsel4utils/src/mapping.c b/libsel4utils/src/mapping.c
@@ -31,6 +31,19 @@ static int map_page(vka_t *vka, vspace_map_page_fn_t map_page_fn, vspace_get_map
     seL4_ARCH_VMAttributes attr = cacheable ? seL4_ARCH_Default_VMAttributes :
                                   seL4_ARCH_Uncached_VMAttributes;
 
+    /* EPT attributes are different than a standard page table. Previously, a kernel bug
+     * masked the problem by always setting EPT mappings to WriteBack. Once the bug was
+     * fixed, every page became uncached, killing VM performance.
+     *
+     * This check ensure the pages are properly cached
+     */
+#ifdef CONFIG_VTX
+    if (seL4_X86_Page_MapEPT == map_page_fn) {
+        attr = cacheable ? seL4_X86_EPT_Default_VMAttributes :
+               seL4_X86_EPT_Uncached_VMAttributes;
+    }
+#endif
+
     *num_objects = 0;
     int error = map_page_fn(frame, root, (seL4_Word) vaddr, rights, attr);
     while (error == seL4_FailedLookup) {