[PATCH RFC v2 12/29] mm: asi: Add basic infrastructure for global non-sensitive mappings

From: Junaid Shahid <[email protected]>

A pseudo-PGD is added to store global non-sensitive ASI mappings.
Actual ASI PGDs copy entries from this pseudo-PGD during asi_init().

Memory can be mapped as globally non-sensitive by calling asi_map()
with ASI_GLOBAL_NONSENSITIVE.

Page tables allocated for global non-sensitive mappings are never
freed.

These page tables are shared between all domains and init_mm, so they
don't need special synchronization.

RFC note: A refactoring/prep commit should be split out of this patch.

Signed-off-by: Junaid Shahid <[email protected]>
Signed-off-by: Brendan Jackman <[email protected]>
---
 arch/x86/include/asm/asi.h |  3 +++
 arch/x86/mm/asi.c          | 37 +++++++++++++++++++++++++++++++++++++
 arch/x86/mm/init_64.c      | 25 ++++++++++++++++---------
 arch/x86/mm/mm_internal.h  |  3 +++
 include/asm-generic/asi.h  |  2 ++
 5 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/asi.h b/arch/x86/include/asm/asi.h
index 33f18be0e268b3a6725196619cbb8d847c21e197..555edb5f292e4d6baba782f51d014aa48dc850b6 100644
--- a/arch/x86/include/asm/asi.h
+++ b/arch/x86/include/asm/asi.h
@@ -120,6 +120,9 @@ struct asi_taint_policy {
 	asi_taints_t set;
 };
 
+extern struct asi __asi_global_nonsensitive;
+#define ASI_GLOBAL_NONSENSITIVE	(&__asi_global_nonsensitive)
+
 /*
  * An ASI domain (struct asi) represents a restricted address space. The
  * unrestricted address space (and user address space under PTI) are not
diff --git a/arch/x86/mm/asi.c b/arch/x86/mm/asi.c
index f2d8fbc0366c289891903e1c2ac6c59b9476d95f..17391ec8b22e3c0903cd5ca29cbb03fcc4cbacce 100644
--- a/arch/x86/mm/asi.c
+++ b/arch/x86/mm/asi.c
@@ -13,6 +13,7 @@
 #include <asm/mmu_context.h>
 #include <asm/traps.h>
 
+#include "mm_internal.h"
 #include "../../../mm/internal.h"
 
 static struct asi_taint_policy *taint_policies[ASI_MAX_NUM_CLASSES];
@@ -26,6 +27,13 @@ const char *asi_class_names[] = {
 DEFINE_PER_CPU_ALIGNED(struct asi *, curr_asi);
 EXPORT_SYMBOL(curr_asi);
 
+static __aligned(PAGE_SIZE) pgd_t asi_global_nonsensitive_pgd[PTRS_PER_PGD];
+
+struct asi __asi_global_nonsensitive = {
+	.pgd = asi_global_nonsensitive_pgd,
+	.mm = &init_mm,
+};
+
 static inline bool asi_class_id_valid(enum asi_class_id class_id)
 {
 	return class_id >= 0 && class_id < ASI_MAX_NUM_CLASSES;
@@ -156,6 +164,31 @@ void __init asi_check_boottime_disable(void)
 		pr_info("ASI enablement ignored due to incomplete implementation.\n");
 }
 
+static int __init asi_global_init(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_ASI))
+		return 0;
+
+	/*
+	 * Lower-level pagetables for global nonsensitive mappings are shared,
+	 * but the PGD has to be copied into each domain during asi_init. To
+	 * avoid needing to synchronize new mappings into pre-existing domains
+	 * we just pre-allocate all of the relevant level N-1 entries so that
+	 * the global nonsensitive PGD already has pointers that can be copied
+	 * when new domains get asi_init()ed.
+	 */
+	preallocate_sub_pgd_pages(asi_global_nonsensitive_pgd,
+				  PAGE_OFFSET,
+				  PAGE_OFFSET + PFN_PHYS(max_pfn) - 1,
+				  "ASI Global Non-sensitive direct map");
+	preallocate_sub_pgd_pages(asi_global_nonsensitive_pgd,
+				  VMALLOC_START, VMALLOC_END,
+				  "ASI Global Non-sensitive vmalloc");
+
+	return 0;
+}
+subsys_initcall(asi_global_init)
+
 static void __asi_destroy(struct asi *asi)
 {
 	WARN_ON_ONCE(asi->ref_count <= 0);
@@ -170,6 +203,7 @@ int asi_init(struct mm_struct *mm, enum asi_class_id class_id, struct asi **out_
 {
 	struct asi *asi;
 	int err = 0;
+	uint i;
 
 	*out_asi = NULL;
 
@@ -203,6 +237,9 @@ int asi_init(struct mm_struct *mm, enum asi_class_id class_id, struct asi **out_
 	asi->mm = mm;
 	asi->class_id = class_id;
 
+	for (i = KERNEL_PGD_BOUNDARY; i < PTRS_PER_PGD; i++)
+		set_pgd(asi->pgd + i, asi_global_nonsensitive_pgd[i]);
+
 exit_unlock:
 	if (err)
 		__asi_destroy(asi);
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index ff253648706fa9cd49169a54882014a72ad540cf..9d358a05c4e18ac6d5e115de111758ea6cdd37f2 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1288,18 +1288,15 @@ static void __init register_page_bootmem_info(void)
 #endif
 }
 
-/*
- * Pre-allocates page-table pages for the vmalloc area in the kernel page-table.
- * Only the level which needs to be synchronized between all page-tables is
- * allocated because the synchronization can be expensive.
- */
-static void __init preallocate_vmalloc_pages(void)
+/* Initialize empty pagetables at the level below PGD.  */
+void __init preallocate_sub_pgd_pages(pgd_t *pgd_table, ulong start,
+				      ulong end, const char *name)
 {
 	unsigned long addr;
 	const char *lvl;
 
-	for (addr = VMALLOC_START; addr <= VMEMORY_END; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
-		pgd_t *pgd = pgd_offset_k(addr);
+	for (addr = start; addr <= end; addr = ALIGN(addr + 1, PGDIR_SIZE)) {
+		pgd_t *pgd = pgd_offset_pgd(pgd_table, addr);
 		p4d_t *p4d;
 		pud_t *pud;
 
@@ -1335,7 +1332,17 @@ static void __init preallocate_vmalloc_pages(void)
 	 * The pages have to be there now or they will be missing in
 	 * process page-tables later.
 	 */
-	panic("Failed to pre-allocate %s pages for vmalloc area\n", lvl);
+	panic("Failed to pre-allocate %s pages for %s area\n", lvl, name);
+}
+
+/*
+ * Pre-allocates page-table pages for the vmalloc area in the kernel page-table.
+ * Only the level which needs to be synchronized between all page-tables is
+ * allocated because the synchronization can be expensive.
+ */
+static void __init preallocate_vmalloc_pages(void)
+{
+	preallocate_sub_pgd_pages(init_mm.pgd, VMALLOC_START, VMEMORY_END, "vmalloc");
 }
 
 void __init mem_init(void)
diff --git a/arch/x86/mm/mm_internal.h b/arch/x86/mm/mm_internal.h
index 3f37b5c80bb32ff34656a20789449da92e853eb6..1203a977edcd523589ad88a37aab01398a10a129 100644
--- a/arch/x86/mm/mm_internal.h
+++ b/arch/x86/mm/mm_internal.h
@@ -25,4 +25,7 @@ void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);
 
 extern unsigned long tlb_single_page_flush_ceiling;
 
+extern void preallocate_sub_pgd_pages(pgd_t *pgd_table, ulong start,
+				      ulong end, const char *name);
+
 #endif	/* __X86_MM_INTERNAL_H */
diff --git a/include/asm-generic/asi.h b/include/asm-generic/asi.h
index 5be8f7d657ba0bc2196e333f62b084d0c9eef7b6..7867b8c23449058a1dd06308ab5351e0d210a489 100644
--- a/include/asm-generic/asi.h
+++ b/include/asm-generic/asi.h
@@ -23,6 +23,8 @@ typedef u8 asi_taints_t;
 
 #ifndef CONFIG_MITIGATION_ADDRESS_SPACE_ISOLATION
 
+#define ASI_GLOBAL_NONSENSITIVE		NULL
+
 struct asi_hooks {};
 struct asi {};
 

-- 
2.47.1.613.gc27f4b7a9f-goog