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>

5 files changed, 58 insertions, 5 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index dfd908630631..d66f9db3e6db 100644
--- a/arch/arm64/Kconfig
+++ b/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
diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index 0e8cc3b85bb8..2b1e5def2e49 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/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)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 7fa6ad48d574..c5cd2c599b24 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/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
 
 /*
diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
index 5141282e47d5..713561e5bcab 100644
--- a/arch/arm64/kernel/irq.c
+++ b/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)
 {
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 71565386d063..fe56c268a7d9 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/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