arm64: add basic VMAP_STACK support

This patch enables arm64 to be built with vmap'd task and IRQ stacks.

As vmap'd stacks are mapped at page granularity, stacks must be a multiple of
PAGE_SIZE. This means that a 64K page kernel must use stacks of at least 64K in
size.

To minimize the increase in Image size, IRQ stacks are dynamically allocated at
boot time, rather than embedding the boot CPU's IRQ stack in the kernel image.

This patch was co-authored by Ard Biesheuvel and Mark Rutland.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>

arch/arm64/Kconfig

@@ -75,6 +75,7 @@ config ARM64
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
+	select HAVE_ARCH_VMAP_STACK
 	select HAVE_ARM_SMCCC
 	select HAVE_EBPF_JIT
 	select HAVE_C_RECORDMCOUNT

arch/arm64/include/asm/efi.h

@@ -49,7 +49,12 @@ int efi_set_mapping_permissions(struct mm_struct *mm, efi_memory_desc_t *md);
  */
 #define EFI_FDT_ALIGN	SZ_2M   /* used by allocate_new_fdt_and_exit_boot() */
 
-#define EFI_KIMG_ALIGN	SEGMENT_ALIGN
+/*
+ * In some configurations (e.g. VMAP_STACK && 64K pages), stacks built into the
+ * kernel need greater alignment than we require the segments to be padded to.
+ */
+#define EFI_KIMG_ALIGN	\
+	(SEGMENT_ALIGN > THREAD_ALIGN ? SEGMENT_ALIGN : THREAD_ALIGN)
 
 /* on arm64, the FDT may be located anywhere in system RAM */
 static inline unsigned long efi_get_max_fdt_addr(unsigned long dram_base)

arch/arm64/include/asm/memory.h

@@ -102,7 +102,17 @@
 #define KASAN_SHADOW_SIZE	(0)
 #endif
 
-#define THREAD_SHIFT		14
+#define MIN_THREAD_SHIFT	14
+
+/*
+ * VMAP'd stacks are allocated at page granularity, so we must ensure that such
+ * stacks are a multiple of page size.
+ */
+#if defined(CONFIG_VMAP_STACK) && (MIN_THREAD_SHIFT < PAGE_SHIFT)
+#define THREAD_SHIFT		PAGE_SHIFT
+#else
+#define THREAD_SHIFT		MIN_THREAD_SHIFT
+#endif
 
 #if THREAD_SHIFT >= PAGE_SHIFT
 #define THREAD_SIZE_ORDER	(THREAD_SHIFT - PAGE_SHIFT)
@@ -110,6 +120,17 @@
 
 #define THREAD_SIZE		(UL(1) << THREAD_SHIFT)
 
+/*
+ * By aligning VMAP'd stacks to 2 * THREAD_SIZE, we can detect overflow by
+ * checking sp & (1 << THREAD_SHIFT), which we can do cheaply in the entry
+ * assembly.
+ */
+#ifdef CONFIG_VMAP_STACK
+#define THREAD_ALIGN		(2 * THREAD_SIZE)
+#else
+#define THREAD_ALIGN		THREAD_SIZE
+#endif
+
 #define IRQ_STACK_SIZE		THREAD_SIZE
 
 /*

arch/arm64/kernel/irq.c

@@ -23,15 +23,15 @@
 
 #include <linux/kernel_stat.h>
 #include <linux/irq.h>
+#include <linux/memory.h>
 #include <linux/smp.h>
 #include <linux/init.h>
 #include <linux/irqchip.h>
 #include <linux/seq_file.h>
+#include <linux/vmalloc.h>
 
 unsigned long irq_err_count;
 
-/* irq stack only needs to be 16 byte aligned - not IRQ_STACK_SIZE aligned. */
-DEFINE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack) __aligned(16);
 DEFINE_PER_CPU(unsigned long *, irq_stack_ptr);
 
 int arch_show_interrupts(struct seq_file *p, int prec)
@@ -51,6 +51,31 @@ void __init set_handle_irq(void (*handle_irq)(struct pt_regs *))
 	handle_arch_irq = handle_irq;
 }
 
+#ifdef CONFIG_VMAP_STACK
+static void init_irq_stacks(void)
+{
+	int cpu;
+	unsigned long *p;
+
+	for_each_possible_cpu(cpu) {
+		/*
+		* To ensure that VMAP'd stack overflow detection works
+		* correctly, the IRQ stacks need to have the same
+		* alignment as other stacks.
+		*/
+		p = __vmalloc_node_range(IRQ_STACK_SIZE, THREAD_ALIGN,
+					 VMALLOC_START, VMALLOC_END,
+					 THREADINFO_GFP, PAGE_KERNEL,
+					 0, cpu_to_node(cpu),
+					 __builtin_return_address(0));
+
+		per_cpu(irq_stack_ptr, cpu) = p;
+	}
+}
+#else
+/* irq stack only needs to be 16 byte aligned - not IRQ_STACK_SIZE aligned. */
+DEFINE_PER_CPU_ALIGNED(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack);
+
 static void init_irq_stacks(void)
 {
 	int cpu;
@@ -58,6 +83,7 @@ static void init_irq_stacks(void)
 	for_each_possible_cpu(cpu)
 		per_cpu(irq_stack_ptr, cpu) = per_cpu(irq_stack, cpu);
 }
+#endif
 
 void __init init_IRQ(void)
 {

arch/arm64/kernel/vmlinux.lds.S

@@ -176,7 +176,7 @@ SECTIONS
 
 	_data = .;
 	_sdata = .;
-	RW_DATA_SECTION(L1_CACHE_BYTES, PAGE_SIZE, THREAD_SIZE)
+	RW_DATA_SECTION(L1_CACHE_BYTES, PAGE_SIZE, THREAD_ALIGN)
 
 	/*
 	 * Data written with the MMU off but read with the MMU on requires