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Subject[PATCH v2 18/18] x86/entry/64: Move the IST stacks into cpu_entry_area
Date
The IST stacks are needed when an IST exception occurs and are
accessed before any kernel code at all runs. Move them into
cpu_entry_area.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
arch/x86/include/asm/fixmap.h | 10 ++++++++++
arch/x86/kernel/cpu/common.c | 40 +++++++++++++++++++++++++---------------
2 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index f13ee74d2d58..c9269d1921c5 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -61,6 +61,16 @@ struct cpu_entry_area
struct tss_struct tss;

char entry_trampoline[PAGE_SIZE];
+
+#ifdef CONFIG_X86_64
+ /*
+ * Exception stacks used for IST entries.
+ *
+ * In the future, this should have a separate slot for each stack
+ * with guard pages between them.
+ */
+ char exception_stacks[(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ];
+#endif
};

#define CPU_ENTRY_AREA_PAGES (sizeof(struct cpu_entry_area) / PAGE_SIZE)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 272cc62cdcbd..1f7e7121c8d2 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -503,6 +503,22 @@ static void set_percpu_fixmap_pages(int fixmap_index, void *ptr, int pages,
DEFINE_PER_CPU(struct cpu_entry_area *, cpu_entry_area);
#endif

+#ifdef CONFIG_X86_64
+/*
+ * Special IST stacks which the CPU switches to when it calls
+ * an IST-marked descriptor entry. Up to 7 stacks (hardware
+ * limit), all of them are 4K, except the debug stack which
+ * is 8K.
+ */
+static const unsigned int exception_stack_sizes[N_EXCEPTION_STACKS] = {
+ [0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STKSZ,
+ [DEBUG_STACK - 1] = DEBUG_STKSZ
+};
+
+static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
+ [(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
+#endif
+
/* Setup the fixmap mappings only once per-processor */
static inline void setup_cpu_entry_area(int cpu)
{
@@ -558,6 +574,14 @@ static inline void setup_cpu_entry_area(int cpu)
#endif

#ifdef CONFIG_X86_64
+ BUILD_BUG_ON(sizeof(exception_stacks) % PAGE_SIZE != 0);
+ BUILD_BUG_ON(sizeof(exception_stacks) !=
+ sizeof(((struct cpu_entry_area *)0)->exception_stacks));
+ set_percpu_fixmap_pages(get_cpu_entry_area_index(cpu, exception_stacks),
+ &per_cpu(exception_stacks, cpu),
+ sizeof(exception_stacks) / PAGE_SIZE,
+ PAGE_KERNEL);
+
__set_fixmap(get_cpu_entry_area_index(cpu, entry_trampoline),
__pa_symbol(_entry_trampoline), PAGE_KERNEL_RX);
#endif
@@ -1408,20 +1432,6 @@ DEFINE_PER_CPU(unsigned int, irq_count) __visible = -1;
DEFINE_PER_CPU(int, __preempt_count) = INIT_PREEMPT_COUNT;
EXPORT_PER_CPU_SYMBOL(__preempt_count);

-/*
- * Special IST stacks which the CPU switches to when it calls
- * an IST-marked descriptor entry. Up to 7 stacks (hardware
- * limit), all of them are 4K, except the debug stack which
- * is 8K.
- */
-static const unsigned int exception_stack_sizes[N_EXCEPTION_STACKS] = {
- [0 ... N_EXCEPTION_STACKS - 1] = EXCEPTION_STKSZ,
- [DEBUG_STACK - 1] = DEBUG_STKSZ
-};
-
-static DEFINE_PER_CPU_PAGE_ALIGNED(char, exception_stacks
- [(N_EXCEPTION_STACKS - 1) * EXCEPTION_STKSZ + DEBUG_STKSZ]);
-
/* May not be marked __init: used by software suspend */
void syscall_init(void)
{
@@ -1627,7 +1637,7 @@ void cpu_init(void)
* set up and load the per-CPU TSS
*/
if (!oist->ist[0]) {
- char *estacks = per_cpu(exception_stacks, cpu);
+ char *estacks = get_cpu_entry_area(cpu)->exception_stacks;

for (v = 0; v < N_EXCEPTION_STACKS; v++) {
estacks += exception_stack_sizes[v];
--
2.13.6
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