[RFC PATCH v5 03/12] __wr_after_init: Core and default arch

@@ -814,6 +814,13 @@ config ARCH_HAS_PRMEM
 	  architecture specific symbol stating that the architecture provides
 	  a back-end function for the write rare operation.
 
+config ARCH_HAS_PRMEM_HEADER
+	def_bool n
+	depends on ARCH_HAS_PRMEM
+	help
+	  architecture specific symbol stating that the architecture provides
+	  own specific header back-end for the write rare operation.
+
 config PRMEM
 	bool "Write protect critical data that doesn't need high write speed."
 	depends on ARCH_HAS_PRMEM

@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * prmem.h: Header for memory protection library - generic part
+ *
+ * (C) Copyright 2018-2019 Huawei Technologies Co. Ltd.
+ * Author: Igor Stoppa <igor.stoppa@huawei.com>
+ */
+
+#ifndef _LINUX_PRMEM_H
+#define _LINUX_PRMEM_H
+
+#include <linux/set_memory.h>
+#include <linux/mutex.h>
+#include <linux/mm.h>
+
+#ifndef CONFIG_PRMEM
+
+static inline void *wr_memset(void *p, int c, __kernel_size_t n)
+{
+	return memset(p, c, n);
+}
+
+static inline void *wr_memcpy(void *p, const void *q, __kernel_size_t n)
+{
+	return memcpy(p, q, n);
+}
+
+#define wr_assign(var, val)	((var) = (val))
+#define wr_rcu_assign_pointer(p, v)	rcu_assign_pointer(p, v)
+
+#else
+
+void *wr_memset(void *p, int c, __kernel_size_t n);
+void *wr_memcpy(void *p, const void *q, __kernel_size_t n);
+
+/**
+ * wr_assign() - sets a write-rare variable to a specified value
+ * @var: the variable to set
+ * @val: the new value
+ *
+ * Returns: the variable
+ */
+
+#define wr_assign(dst, val) ({			\
+	typeof(dst) tmp = (typeof(dst))val;	\
+						\
+	wr_memcpy(&dst, &tmp, sizeof(dst));	\
+	dst;					\
+})
+
+/**
+ * wr_rcu_assign_pointer() - initialize a pointer in rcu mode
+ * @p: the rcu pointer - it MUST be aligned to a machine word
+ * @v: the new value
+ *
+ * Returns the value assigned to the rcu pointer.
+ *
+ * It is provided as macro, to match rcu_assign_pointer()
+ * The rcu_assign_pointer() is implemented as equivalent of:
+ *
+ * smp_mb();
+ * WRITE_ONCE();
+ */
+#define wr_rcu_assign_pointer(p, v) ({	\
+	smp_mb();			\
+	wr_assign(p, v);		\
+	p;				\
+})
+#endif
+#endif

@@ -58,6 +58,7 @@ obj-$(CONFIG_SPARSEMEM)	+= sparse.o
 obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
 obj-$(CONFIG_SLOB) += slob.o
 obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
+obj-$(CONFIG_PRMEM) += prmem.o
 obj-$(CONFIG_KSM) += ksm.o
 obj-$(CONFIG_PAGE_POISONING) += page_poison.o
 obj-$(CONFIG_SLAB) += slab.o

@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * prmem.c: Memory Protection Library
+ *
+ * (C) Copyright 2018-2019 Huawei Technologies Co. Ltd.
+ * Author: Igor Stoppa <igor.stoppa@huawei.com>
+ */
+
+#include <linux/mmu_context.h>
+#include <linux/uaccess.h>
+
+/*
+ * In case an architecture needs a different declaration of struct
+ * wr_state, it can select ARCH_HAS_PRMEM_HEADER and provide its own
+ * version, accompanied by matching __wr_enable() and __wr_disable()
+ */
+#ifdef CONFIG_ARCH_HAS_PRMEM_HEADER
+#include <asm/prmem.h>
+#else
+
+struct wr_state {
+	struct mm_struct *prev;
+};
+
+#endif
+
+
+__ro_after_init struct mm_struct *wr_mm;
+__ro_after_init unsigned long wr_base;
+
+/*
+ * Default implementation of arch-specific functionality.
+ * Each arch can override the parts that require special handling.
+ */
+unsigned long __init __weak __init_wr_base(void)
+{
+	return 0UL;
+}
+
+void * __weak __wr_addr(void *addr)
+{
+	return (void *)(wr_base + (unsigned long)addr);
+}
+
+void __weak __wr_enable(struct wr_state *state)
+{
+	lockdep_assert_irqs_disabled();
+	state->prev = current->active_mm;
+	switch_mm_irqs_off(NULL, wr_mm, current);
+}
+
+void __weak __wr_disable(struct wr_state *state)
+{
+	lockdep_assert_irqs_disabled();
+	switch_mm_irqs_off(NULL, state->prev, current);
+}
+
+bool __init __weak __wr_map_address(unsigned long addr)
+{
+	spinlock_t *ptl;
+	pte_t pte;
+	pte_t *ptep;
+	unsigned long wr_addr;
+	struct page *page = virt_to_page(addr);
+
+	if (unlikely(!page))
+		return false;
+	wr_addr = (unsigned long)__wr_addr((void *)addr);
+
+	/* The lock is not needed, but avoids open-coding. */
+	ptep = get_locked_pte(wr_mm, wr_addr, &ptl);
+	if (unlikely(!ptep))
+		return false;
+
+	pte = mk_pte(page, PAGE_KERNEL);
+	set_pte_at(wr_mm, wr_addr, ptep, pte);
+	spin_unlock(ptl);
+	return true;
+}
+
+
+#if ((defined(INLINE_COPY_TO_USER) && !defined(memset_user)) || \
+     !defined(INLINE_COPY_TO_USER))
+unsigned long __weak memset_user(void __user *to, int c, unsigned long n)
+{
+	unsigned long i;
+	char b = (char)c;
+
+	for (i = 0; i < n; i++)
+		copy_to_user((void __user *)((unsigned long)to + i), &b, 1);
+	return n;
+}
+#endif
+
+void * __weak __wr_memset(void *p, int c, __kernel_size_t n)
+{
+	return (void *)memset_user((void __user *)p, (u8)c, n);
+}
+
+void * __weak __wr_memcpy(void *p, const void *q, __kernel_size_t n)
+{
+	return (void *)copy_to_user((void __user *)p, q, n);
+}
+
+/*
+ * The following two variables are statically allocated by the linker
+ * script at the boundaries of the memory region (rounded up to
+ * multiples of PAGE_SIZE) reserved for __wr_after_init.
+ */
+extern long __start_wr_after_init;
+extern long __end_wr_after_init;
+static unsigned long start = (unsigned long)&__start_wr_after_init;
+static unsigned long end = (unsigned long)&__end_wr_after_init;
+static inline bool is_wr_after_init(void *p, __kernel_size_t n)
+{
+	unsigned long low = (unsigned long)p;
+	unsigned long high = low + n;
+
+	return likely(start <= low && high <= end);
+}
+
+#define wr_mem_is_writable() (system_state == SYSTEM_BOOTING)
+
+/**
+ * wr_memcpy() - copies n bytes from q to p
+ * @p: beginning of the memory to write to
+ * @q: beginning of the memory to read from
+ * @n: amount of bytes to copy
+ *
+ * Returns pointer to the destination
+ */
+void *wr_memcpy(void *p, const void *q, __kernel_size_t n)
+{
+	struct wr_state state;
+	void *wr_addr;
+
+	if (WARN_ONCE(!is_wr_after_init(p, n), "Invalid WR range."))
+		return p;
+
+	if (unlikely(wr_mem_is_writable()))
+		return memcpy(p, q, n);
+
+	wr_addr = __wr_addr(p);
+	local_irq_disable();
+	__wr_enable(&state);
+	__wr_memcpy(wr_addr, q, n);
+	__wr_disable(&state);
+	local_irq_enable();
+	return p;
+}
+
+/**
+ * wr_memset() - sets n bytes of the destination p to the c value
+ * @p: beginning of the memory to write to
+ * @c: byte to replicate
+ * @n: amount of bytes to copy
+ *
+ * Returns pointer to the destination
+ */
+void *wr_memset(void *p, int c, __kernel_size_t n)
+{
+	struct wr_state state;
+	void *wr_addr;
+
+	if (WARN_ONCE(!is_wr_after_init(p, n), "Invalid WR range."))
+		return p;
+
+	if (unlikely(wr_mem_is_writable()))
+		return memset(p, c, n);
+
+	wr_addr = __wr_addr(p);
+	local_irq_disable();
+	__wr_enable(&state);
+	__wr_memset(wr_addr, c, n);
+	__wr_disable(&state);
+	local_irq_enable();
+	return p;
+}
+
+struct mm_struct *copy_init_mm(void);
+void __init wr_init(void)
+{
+	unsigned long addr;
+
+	wr_mm = copy_init_mm();
+	BUG_ON(!wr_mm);
+
+	wr_base = __init_wr_base();
+
+	/* Create alternate mapping for the entire wr_after_init range. */
+	for (addr = start; addr < end; addr += PAGE_SIZE)
+		BUG_ON(!__wr_map_address(addr));
+}