arm64: kvm: Introduce nvhe stack size constants

Refactor nvhe stack code to use NVHE_STACK_SIZE/SHIFT constants,
instead of directly using PAGE_SIZE/SHIFT. This makes the code a bit
easier to read, without introducing any functional changes.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Link: https://lore.kernel.org/r/20241112003336.1375584-1-kaleshsingh@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/include/asm/memory.h

@@ -145,13 +145,16 @@
 
 #define OVERFLOW_STACK_SIZE	SZ_4K
 
+#define NVHE_STACK_SHIFT       PAGE_SHIFT
+#define NVHE_STACK_SIZE        (UL(1) << NVHE_STACK_SHIFT)
+
 /*
  * With the minimum frame size of [x29, x30], exactly half the combined
  * sizes of the hyp and overflow stacks is the maximum size needed to
  * save the unwinded stacktrace; plus an additional entry to delimit the
  * end.
  */
-#define NVHE_STACKTRACE_SIZE	((OVERFLOW_STACK_SIZE + PAGE_SIZE) / 2 + sizeof(long))
+#define NVHE_STACKTRACE_SIZE	((OVERFLOW_STACK_SIZE + NVHE_STACK_SIZE) / 2 + sizeof(long))
 
 /*
  * Alignment of kernel segments (e.g. .text, .data).

arch/arm64/include/asm/stacktrace/nvhe.h

@@ -47,7 +47,7 @@ static inline void kvm_nvhe_unwind_init(struct unwind_state *state,
 
 DECLARE_KVM_NVHE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack);
 DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_stacktrace_info, kvm_stacktrace_info);
-DECLARE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
+DECLARE_PER_CPU(unsigned long, kvm_arm_hyp_stack_base);
 
 void kvm_nvhe_dump_backtrace(unsigned long hyp_offset);
 

arch/arm64/kvm/arm.c

@@ -61,7 +61,7 @@ static enum kvm_wfx_trap_policy kvm_wfe_trap_policy __read_mostly = KVM_WFX_NOTR
 
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
 
-DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
+DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_base);
 DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);
 
 DECLARE_KVM_NVHE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
@@ -2339,7 +2339,7 @@ static void __init teardown_hyp_mode(void)
 
 	free_hyp_pgds();
 	for_each_possible_cpu(cpu) {
-		free_page(per_cpu(kvm_arm_hyp_stack_page, cpu));
+		free_pages(per_cpu(kvm_arm_hyp_stack_base, cpu), NVHE_STACK_SHIFT - PAGE_SHIFT);
 		free_pages(kvm_nvhe_sym(kvm_arm_hyp_percpu_base)[cpu], nvhe_percpu_order());
 
 		if (free_sve) {
@@ -2527,15 +2527,15 @@ static int __init init_hyp_mode(void)
 	 * Allocate stack pages for Hypervisor-mode
 	 */
 	for_each_possible_cpu(cpu) {
-		unsigned long stack_page;
+		unsigned long stack_base;
 
-		stack_page = __get_free_page(GFP_KERNEL);
-		if (!stack_page) {
+		stack_base = __get_free_pages(GFP_KERNEL, NVHE_STACK_SHIFT - PAGE_SHIFT);
+		if (!stack_base) {
 			err = -ENOMEM;
 			goto out_err;
 		}
 
-		per_cpu(kvm_arm_hyp_stack_page, cpu) = stack_page;
+		per_cpu(kvm_arm_hyp_stack_base, cpu) = stack_base;
 	}
 
 	/*
@@ -2604,9 +2604,9 @@ static int __init init_hyp_mode(void)
 	 */
 	for_each_possible_cpu(cpu) {
 		struct kvm_nvhe_init_params *params = per_cpu_ptr_nvhe_sym(kvm_init_params, cpu);
-		char *stack_page = (char *)per_cpu(kvm_arm_hyp_stack_page, cpu);
+		char *stack_base = (char *)per_cpu(kvm_arm_hyp_stack_base, cpu);
 
-		err = create_hyp_stack(__pa(stack_page), &params->stack_hyp_va);
+		err = create_hyp_stack(__pa(stack_base), &params->stack_hyp_va);
 		if (err) {
 			kvm_err("Cannot map hyp stack\n");
 			goto out_err;
@@ -2618,7 +2618,7 @@ static int __init init_hyp_mode(void)
 		 * __hyp_pa() won't do the right thing there, since the stack
 		 * has been mapped in the flexible private VA space.
 		 */
-		params->stack_pa = __pa(stack_page);
+		params->stack_pa = __pa(stack_base);
 	}
 
 	for_each_possible_cpu(cpu) {

arch/arm64/kvm/hyp/nvhe/host.S

@@ -188,12 +188,12 @@ SYM_FUNC_END(__host_hvc)
 
 	/*
 	 * Test whether the SP has overflowed, without corrupting a GPR.
-	 * nVHE hypervisor stacks are aligned so that the PAGE_SHIFT bit
+	 * nVHE hypervisor stacks are aligned so that the NVHE_STACK_SHIFT bit
 	 * of SP should always be 1.
 	 */
 	add	sp, sp, x0			// sp' = sp + x0
 	sub	x0, sp, x0			// x0' = sp' - x0 = (sp + x0) - x0 = sp
-	tbz	x0, #PAGE_SHIFT, .L__hyp_sp_overflow\@
+	tbz	x0, #NVHE_STACK_SHIFT, .L__hyp_sp_overflow\@
 	sub	x0, sp, x0			// x0'' = sp' - x0' = (sp + x0) - sp = x0
 	sub	sp, sp, x0			// sp'' = sp' - x0 = (sp + x0) - x0 = sp
 

arch/arm64/kvm/hyp/nvhe/mm.c

@@ -360,10 +360,10 @@ int pkvm_create_stack(phys_addr_t phys, unsigned long *haddr)
 
 	prev_base = __io_map_base;
 	/*
-	 * Efficient stack verification using the PAGE_SHIFT bit implies
+	 * Efficient stack verification using the NVHE_STACK_SHIFT bit implies
 	 * an alignment of our allocation on the order of the size.
 	 */
-	size = PAGE_SIZE * 2;
+	size = NVHE_STACK_SIZE * 2;
 	addr = ALIGN(__io_map_base, size);
 
 	ret = __pkvm_alloc_private_va_range(addr, size);
@@ -373,12 +373,12 @@ int pkvm_create_stack(phys_addr_t phys, unsigned long *haddr)
 		 * at the higher address and leave the lower guard page
 		 * unbacked.
 		 *
-		 * Any valid stack address now has the PAGE_SHIFT bit as 1
+		 * Any valid stack address now has the NVHE_STACK_SHIFT bit as 1
 		 * and addresses corresponding to the guard page have the
-		 * PAGE_SHIFT bit as 0 - this is used for overflow detection.
+		 * NVHE_STACK_SHIFT bit as 0 - this is used for overflow detection.
 		 */
-		ret = kvm_pgtable_hyp_map(&pkvm_pgtable, addr + PAGE_SIZE,
-					  PAGE_SIZE, phys, PAGE_HYP);
+		ret = kvm_pgtable_hyp_map(&pkvm_pgtable, addr + NVHE_STACK_SIZE,
+					  NVHE_STACK_SIZE, phys, PAGE_HYP);
 		if (ret)
 			__io_map_base = prev_base;
 	}

arch/arm64/kvm/hyp/nvhe/stacktrace.c

@@ -28,7 +28,7 @@ static void hyp_prepare_backtrace(unsigned long fp, unsigned long pc)
 	struct kvm_nvhe_stacktrace_info *stacktrace_info = this_cpu_ptr(&kvm_stacktrace_info);
 	struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
 
-	stacktrace_info->stack_base = (unsigned long)(params->stack_hyp_va - PAGE_SIZE);
+	stacktrace_info->stack_base = (unsigned long)(params->stack_hyp_va - NVHE_STACK_SIZE);
 	stacktrace_info->overflow_stack_base = (unsigned long)this_cpu_ptr(overflow_stack);
 	stacktrace_info->fp = fp;
 	stacktrace_info->pc = pc;
@@ -54,7 +54,7 @@ static struct stack_info stackinfo_get_hyp(void)
 {
 	struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
 	unsigned long high = params->stack_hyp_va;
-	unsigned long low = high - PAGE_SIZE;
+	unsigned long low = high - NVHE_STACK_SIZE;
 
 	return (struct stack_info) {
 		.low = low,

arch/arm64/kvm/mmu.c

@@ -706,10 +706,10 @@ int create_hyp_stack(phys_addr_t phys_addr, unsigned long *haddr)
 
 	mutex_lock(&kvm_hyp_pgd_mutex);
 	/*
-	 * Efficient stack verification using the PAGE_SHIFT bit implies
+	 * Efficient stack verification using the NVHE_STACK_SHIFT bit implies
 	 * an alignment of our allocation on the order of the size.
 	 */
-	size = PAGE_SIZE * 2;
+	size = NVHE_STACK_SIZE * 2;
 	base = ALIGN_DOWN(io_map_base - size, size);
 
 	ret = __hyp_alloc_private_va_range(base);
@@ -726,12 +726,12 @@ int create_hyp_stack(phys_addr_t phys_addr, unsigned long *haddr)
 	 * at the higher address and leave the lower guard page
 	 * unbacked.
 	 *
-	 * Any valid stack address now has the PAGE_SHIFT bit as 1
+	 * Any valid stack address now has the NVHE_STACK_SHIFT bit as 1
 	 * and addresses corresponding to the guard page have the
-	 * PAGE_SHIFT bit as 0 - this is used for overflow detection.
+	 * NVHE_STACK_SHIFT bit as 0 - this is used for overflow detection.
 	 */
-	ret = __create_hyp_mappings(base + PAGE_SIZE, PAGE_SIZE, phys_addr,
-				    PAGE_HYP);
+	ret = __create_hyp_mappings(base + NVHE_STACK_SIZE, NVHE_STACK_SIZE,
+				    phys_addr, PAGE_HYP);
 	if (ret)
 		kvm_err("Cannot map hyp stack\n");
 

arch/arm64/kvm/stacktrace.c

@@ -51,7 +51,7 @@ static struct stack_info stackinfo_get_hyp(void)
 	struct kvm_nvhe_stacktrace_info *stacktrace_info
 				= this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);
 	unsigned long low = (unsigned long)stacktrace_info->stack_base;
-	unsigned long high = low + PAGE_SIZE;
+	unsigned long high = low + NVHE_STACK_SIZE;
 
 	return (struct stack_info) {
 		.low = low,
@@ -61,8 +61,8 @@ static struct stack_info stackinfo_get_hyp(void)
 
 static struct stack_info stackinfo_get_hyp_kern_va(void)
 {
-	unsigned long low = (unsigned long)*this_cpu_ptr(&kvm_arm_hyp_stack_page);
-	unsigned long high = low + PAGE_SIZE;
+	unsigned long low = (unsigned long)*this_cpu_ptr(&kvm_arm_hyp_stack_base);
+	unsigned long high = low + NVHE_STACK_SIZE;
 
 	return (struct stack_info) {
 		.low = low,