[RFC PATCH V2 7/7] x86/entry: remove DB1 stack and DB2 hole from cpu entry area

Lai Jiangshan
2020-05-26T01:42:49Z

IST-shift code is removed from entry code, #DB will stick to
DB stack only. So we remove the DB1 stack and the DB2 hole.

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86@kernel.org
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/include/asm/cpu_entry_area.h | 12 +++---------
arch/x86/kernel/asm-offsets_64.c | 4 ----
arch/x86/kernel/dumpstack_64.c | 10 +++-------
arch/x86/mm/cpu_entry_area.c | 4 +---
4 files changed, 7 insertions(+), 23 deletions(-)

diff --git a/arch/x86/include/asm/cpu_entry_area.h b/arch/x86/include/asm/cpu_entry_area.h
index 02c0078d3787..8902fdb7de13 100644
--- a/arch/x86/include/asm/cpu_entry_area.h
+++ b/arch/x86/include/asm/cpu_entry_area.h
@@ -11,15 +11,11 @@
#ifdef CONFIG_X86_64

/* Macro to enforce the same ordering and stack sizes */
-#define ESTACKS_MEMBERS(guardsize, db2_holesize)\
+#define ESTACKS_MEMBERS(guardsize) \
char DF_stack_guard[guardsize]; \
char DF_stack[EXCEPTION_STKSZ]; \
char NMI_stack_guard[guardsize]; \
char NMI_stack[EXCEPTION_STKSZ]; \
- char DB2_stack_guard[guardsize]; \
- char DB2_stack[db2_holesize]; \
- char DB1_stack_guard[guardsize]; \
- char DB1_stack[EXCEPTION_STKSZ]; \
char DB_stack_guard[guardsize]; \
char DB_stack[EXCEPTION_STKSZ]; \
char MCE_stack_guard[guardsize]; \
@@ -28,12 +24,12 @@

/* The exception stacks' physical storage. No guard pages required */
struct exception_stacks {
- ESTACKS_MEMBERS(0, 0)
+ ESTACKS_MEMBERS(0)
};

/* The effective cpu entry area mapping with guard pages. */
struct cea_exception_stacks {
- ESTACKS_MEMBERS(PAGE_SIZE, EXCEPTION_STKSZ)
+ ESTACKS_MEMBERS(PAGE_SIZE)
};

/*
@@ -42,8 +38,6 @@ struct cea_exception_stacks {
enum exception_stack_ordering {
ESTACK_DF,
ESTACK_NMI,
- ESTACK_DB2,
- ESTACK_DB1,
ESTACK_DB,
ESTACK_MCE,
N_EXCEPTION_STACKS
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index 472378330169..4b4974d91d90 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -57,10 +57,6 @@ int main(void)
BLANK();
#undef ENTRY

- DEFINE(DB_STACK_OFFSET, offsetof(struct cea_exception_stacks, DB_stack) -
- offsetof(struct cea_exception_stacks, DB1_stack));
- BLANK();
-
#ifdef CONFIG_STACKPROTECTOR
DEFINE(stack_canary_offset, offsetof(struct fixed_percpu_data, stack_canary));
BLANK();
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 460ae7f66818..6b7051fa3669 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -22,15 +22,13 @@
static const char * const exception_stack_names[] = {
[ ESTACK_DF ] = "#DF",
[ ESTACK_NMI ] = "NMI",
- [ ESTACK_DB2 ] = "#DB2",
- [ ESTACK_DB1 ] = "#DB1",
[ ESTACK_DB ] = "#DB",
[ ESTACK_MCE ] = "#MC",
};

const char *stack_type_name(enum stack_type type)
{
- BUILD_BUG_ON(N_EXCEPTION_STACKS != 6);
+ BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);

if (type == STACK_TYPE_IRQ)
return "IRQ";
@@ -72,14 +70,12 @@ struct estack_pages {
/*
* Array of exception stack page descriptors. If the stack is larger than
* PAGE_SIZE, all pages covering a particular stack will have the same
- * info. The guard pages including the not mapped DB2 stack are zeroed
- * out.
+ * info. The guard pages are zeroed out.
*/
static const
struct estack_pages estack_pages[CEA_ESTACK_PAGES] ____cacheline_aligned = {
EPAGERANGE(DF),
EPAGERANGE(NMI),
- EPAGERANGE(DB1),
EPAGERANGE(DB),
EPAGERANGE(MCE),
};
@@ -91,7 +87,7 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
struct pt_regs *regs;
unsigned int k;

- BUILD_BUG_ON(N_EXCEPTION_STACKS != 6);
+ BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);

begin = (unsigned long)__this_cpu_read(cea_exception_stacks);
/*
diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index 5199d8a1daf1..686af163be20 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -102,12 +102,10 @@ static void __init percpu_setup_exception_stacks(unsigned int cpu)

/*
* The exceptions stack mappings in the per cpu area are protected
- * by guard pages so each stack must be mapped separately. DB2 is
- * not mapped; it just exists to catch triple nesting of #DB.
+ * by guard pages so each stack must be mapped separately.
*/
cea_map_stack(DF);
cea_map_stack(NMI);
- cea_map_stack(DB1);
cea_map_stack(DB);
cea_map_stack(MCE);
}
--
2.20.1