x86: add support for on-demand mappings

This makes x86 compatible with K_MEM_MAP_UNPAGED.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>

arch/Kconfig

@@ -92,6 +92,7 @@ config X86
 	select ARCH_HAS_TIMING_FUNCTIONS
 	select ARCH_HAS_THREAD_LOCAL_STORAGE
 	select ARCH_HAS_DEMAND_PAGING if !X86_64
+	select ARCH_HAS_DEMAND_MAPPING if ARCH_HAS_DEMAND_PAGING
 	select IRQ_OFFLOAD_NESTED if IRQ_OFFLOAD
 	select NEED_LIBC_MEM_PARTITION if USERSPACE && TIMING_FUNCTIONS \
 					  && !BOARD_HAS_TIMING_FUNCTIONS \

arch/x86/core/x86_mmu.c

@@ -1281,6 +1281,12 @@ static pentry_t flags_to_entry(uint32_t flags)
 		entry_flags |= ENTRY_XD;
 	}
 
+	if (IS_ENABLED(CONFIG_DEMAND_MAPPING) && (flags & K_MEM_MAP_UNPAGED) != 0U) {
+		/* same state as in arch_mem_page_out() */
+		entry_flags &= ~MMU_P;
+		entry_flags |= MMU_A;
+	}
+
 	return entry_flags;
 }
 

include/zephyr/arch/x86/mmustructs.h

@@ -32,6 +32,20 @@
 /* Use an PAT bit for this one since it's never set in a mapped PTE */
 #define ARCH_DATA_PAGE_NOT_MAPPED	((uintptr_t)BIT(7))
 
+/*
+ * Special unpaged "location" tags. These are defined as the highest possible
+ * PTE address values unlikely to conflict with backing store locations.
+ * As noted in arch_page_info_get(), those values on PAE systems, whose
+ * pentry_t is larger than uintptr_t get truncated.
+ */
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
+#define ARCH_UNPAGED_ANON_ZERO		((uintptr_t)0x07FFFFFFFFFFF000ULL)
+#define ARCH_UNPAGED_ANON_UNINIT	((uintptr_t)0x07FFFFFFFFFFE000ULL)
+#else
+#define ARCH_UNPAGED_ANON_ZERO		((uintptr_t)0xFFFFF000U)
+#define ARCH_UNPAGED_ANON_UNINIT	((uintptr_t)0xFFFFE000U)
+#endif
+
 /* Always true with 32-bit page tables, don't enable
  * CONFIG_EXECUTE_XOR_WRITE and expect it to work for you
  */