[RFC PATCH 2/6] powerpc/64s: Helpers to switch between linear and vmapped stack pointers

@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+// Helpers for VMAP_STACK on book3s64
+// Copyright (C) 2022 IBM Corporation (Andrew Donnellan)
+
+#ifndef _ASM_POWERPC_BOOK3S_64_STACK_H
+#define _ASM_POWERPC_BOOK3S_64_STACK_H
+
+#include <asm/thread_info.h>
+
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+
+#ifdef __ASSEMBLY__
+// Switch the current stack pointer in r1 between a linear map address and a
+// vmalloc address. Used when we need to go in and out of real mode with
+// CONFIG_VMAP_STACK enabled.
+//
+// tmp: scratch register that can be clobbered
+
+#define SWAP_STACK_LINEAR(tmp)			\
+	ld	tmp, PACAKSTACK_LINEAR_BASE(r13);	\
+	andi.	r1, r1, THREAD_SIZE - 1;		\
+	or	r1, r1, tmp;
+#define SWAP_STACK_VMALLOC(tmp)			\
+	ld	tmp, PACAKSTACK_VMALLOC_BASE(r13);	\
+	andi.	r1, r1, THREAD_SIZE - 1;		\
+	or	r1, r1, tmp;
+
+#else // __ASSEMBLY__
+
+#include <asm/paca.h>
+#include <asm/reg.h>
+#include <linux/mm.h>
+
+#define stack_pa(ptr) (is_vmalloc_addr((ptr)) ? (void *)vmalloc_to_phys((void *)(ptr)) : (void *)ptr)
+
+static __always_inline void swap_stack_linear(void)
+{
+	current_stack_pointer = get_paca()->kstack_linear_base |	\
+		(current_stack_pointer & (THREAD_SIZE - 1));
+}
+
+static __always_inline void swap_stack_vmalloc(void)
+{
+	current_stack_pointer = get_paca()->kstack_vmalloc_base |	\
+		(current_stack_pointer & (THREAD_SIZE - 1));
+}
+
+#endif // __ASSEMBLY__
+
+#else // CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64
+
+#define SWAP_STACK_LINEAR(tmp)
+#define SWAP_STACK_VMALLOC(tmp)
+
+static __always_inline void *stack_pa(void *ptr)
+{
+	return ptr;
+}
+
+static __always_inline void swap_stack_linear(void)
+{
+}
+
+static __always_inline void swap_stack_vmalloc(void)
+{
+}
+
+#endif // CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64
+
+#endif // _ASM_POWERPC_BOOK3S_64_STACK_H

@@ -13,6 +13,7 @@
 #ifndef __ASSEMBLY__
 
 #include <linux/notifier.h>
+#include <asm/book3s/64/stack.h>
 
 /* We calculate number of sg entries based on PAGE_SIZE */
 #define SG_ENTRIES_PER_NODE ((PAGE_SIZE - 16) / sizeof(struct opal_sg_entry))

@@ -163,6 +163,10 @@ struct paca_struct {
 	 */
 	struct task_struct *__current;	/* Pointer to current */
 	u64 kstack;			/* Saved Kernel stack addr */
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+	u64 kstack_vmalloc_base;	/* Base address of stack in the vmalloc mapping */
+	u64 kstack_linear_base;		/* Base address of stack in the linear mapping */
+#endif /* CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64 */
 	u64 saved_r1;			/* r1 save for RTAS calls or PM or EE=0 */
 	u64 saved_msr;			/* MSR saved here by enter_rtas */
 #ifdef CONFIG_PPC64

@@ -132,6 +132,12 @@ struct debug_reg {
 
 struct thread_struct {
 	unsigned long	ksp;		/* Kernel stack pointer */
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+	// Kernel stack base addresses in vmalloc and linear mappings
+	// Used for swapping to linear map in real mode code
+	unsigned long	ksp_vmalloc_base;
+	unsigned long	ksp_linear_base;
+#endif /* CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64 */
 
 #ifdef CONFIG_PPC64
 	unsigned long	ksp_vsid;

@@ -99,6 +99,10 @@ int main(void)
 #endif
 
 	OFFSET(KSP, thread_struct, ksp);
+#ifdef CONFIG_VMAP_STACK
+	OFFSET(KSP_VMALLOC_BASE, thread_struct, ksp_vmalloc_base);
+	OFFSET(KSP_LINEAR_BASE, thread_struct, ksp_linear_base);
+#endif /* CONFIG_VMAP_STACK */
 	OFFSET(PT_REGS, thread_struct, regs);
 #ifdef CONFIG_BOOKE
 	OFFSET(THREAD_NORMSAVES, thread_struct, normsave[0]);

@@ -181,6 +185,10 @@ int main(void)
 	OFFSET(PACAPACAINDEX, paca_struct, paca_index);
 	OFFSET(PACAPROCSTART, paca_struct, cpu_start);
 	OFFSET(PACAKSAVE, paca_struct, kstack);
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+	OFFSET(PACAKSTACK_VMALLOC_BASE, paca_struct, kstack_vmalloc_base);
+	OFFSET(PACAKSTACK_LINEAR_BASE, paca_struct, kstack_linear_base);
+#endif /* CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64 */
 	OFFSET(PACACURRENT, paca_struct, __current);
 	DEFINE(PACA_THREAD_INFO, offsetof(struct paca_struct, __current) +
 				 offsetof(struct task_struct, thread_info));

@@ -253,6 +253,13 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
 	mr	r1,r8		/* start using new stack pointer */
 	std	r7,PACAKSAVE(r13)
 
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+	ld	r8,KSP_LINEAR_BASE(r4)
+	std	r8,PACAKSTACK_LINEAR_BASE(r13)
+	ld	r8,KSP_VMALLOC_BASE(r4)
+	std	r8,PACAKSTACK_VMALLOC_BASE(r13)
+#endif /* CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64 */
+
 	ld	r6,_CCR(r1)
 	mtcrf	0xFF,r6
 

@@ -1782,6 +1782,10 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	kregs = (struct pt_regs *) sp;
 	sp -= STACK_FRAME_OVERHEAD;
 	p->thread.ksp = sp;
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+	p->thread.ksp_vmalloc_base = sp & ~(THREAD_SIZE - 1);
+	p->thread.ksp_linear_base = (u64)__va(vmalloc_to_pfn((void *)sp) << PAGE_SHIFT);
+#endif /* CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64 */
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 	for (i = 0; i < nr_wp_slots(); i++)
 		p->thread.ptrace_bps[i] = NULL;

@@ -60,6 +60,7 @@
 #include <asm/ftrace.h>
 #include <asm/kup.h>
 #include <asm/fadump.h>
+#include <asm/book3s/64/stack.h>
 
 #ifdef DEBUG
 #include <asm/udbg.h>

@@ -1250,6 +1251,12 @@ static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle)
 	paca_ptrs[cpu]->__current = idle;
 	paca_ptrs[cpu]->kstack = (unsigned long)task_stack_page(idle) +
 				 THREAD_SIZE - STACK_FRAME_OVERHEAD;
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+	paca_ptrs[cpu]->kstack_linear_base = is_vmalloc_addr((void *)paca_ptrs[cpu]->kstack) ?
+		vmalloc_to_phys((void *)(paca_ptrs[cpu]->kstack)) :
+		paca_ptrs[cpu]->kstack;
+	paca_ptrs[cpu]->kstack_vmalloc_base = paca_ptrs[cpu]->kstack & (THREAD_SIZE - 1);
+#endif // CONFIG_VMAP_STACK && CONFIG_PPC_BOOK3S_64
 #endif
 	task_thread_info(idle)->cpu = cpu;
 	secondary_current = current_set[cpu] = idle;

@@ -2697,6 +2697,10 @@ static void dump_one_paca(int cpu)
 	DUMP(p, __current, "%-*px");
 	DUMP(p, kstack, "%#-*llx");
 	printf(" %-*s = 0x%016llx\n", 25, "kstack_base", p->kstack & ~(THREAD_SIZE - 1));
+#if defined(CONFIG_VMAP_STACK) && defined(CONFIG_PPC_BOOK3S_64)
+	DUMP(p, kstack_linear_base, "%#-*llx");
+	DUMP(p, kstack_vmalloc_base, "%#-*llx");
+#endif
 #ifdef CONFIG_STACKPROTECTOR
 	DUMP(p, canary, "%#-*lx");
 #endif