[PATCH 2/3] riscv/mm: Implement kmap() and kmap_atomic()

[Eric Lin]

Both kmap() and kmap_atomic() help kernel to create
temporary mappings from a highmem page.

Be aware that use kmap() might put calling function to sleep
and it cannot use in interrupt context. kmap_atomic() is an
atomic version of kmap() which can be used in interrupt context
and it is faster than kmap() because it doesn't hold a lock.

Here we preserve some memory slots from fixmap region for
kmap_atomic() and kmap() will use pkmap region.

Signed-off-by: Eric Lin <tesheng@xxxxxxxxxxxxx>
Cc: Alan Kao <alankao@xxxxxxxxxxxxx>
---
 arch/riscv/include/asm/fixmap.h  |  9 +++-
 arch/riscv/include/asm/highmem.h | 30 +++++++++++++
 arch/riscv/include/asm/pgtable.h |  5 +++
 arch/riscv/mm/Makefile           |  1 +
 arch/riscv/mm/highmem.c          | 74 ++++++++++++++++++++++++++++++++
 5 files changed, 118 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/mm/highmem.c

diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
index 42d2c42f3cc9..8dedc2bf2917 100644
--- a/arch/riscv/include/asm/fixmap.h
+++ b/arch/riscv/include/asm/fixmap.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2019 Western Digital Corporation or its affiliates.
+ * Copyright (C) 2020 Andes Technology Corporation
  */
 
 #ifndef _ASM_RISCV_FIXMAP_H
@@ -10,6 +11,7 @@
 #include <linux/sizes.h>
 #include <asm/page.h>
 #include <asm/pgtable.h>
+#include <asm/kmap_types.h>
 
 #ifdef CONFIG_MMU
 /*
@@ -28,7 +30,12 @@ enum fixed_addresses {
 	FIX_PTE,
 	FIX_PMD,
 	FIX_EARLYCON_MEM_BASE,
-	__end_of_fixed_addresses
+#ifdef CONFIG_HIGHMEM
+	FIX_KMAP_RESERVED,
+	FIX_KMAP_BEGIN,
+	FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS),
+#endif
+	__end_of_fixed_addresses,
 };
 
 #define FIXMAP_PAGE_IO		PAGE_KERNEL
diff --git a/arch/riscv/include/asm/highmem.h b/arch/riscv/include/asm/highmem.h
index 7fc79e58f607..ec7c83d55830 100644
--- a/arch/riscv/include/asm/highmem.h
+++ b/arch/riscv/include/asm/highmem.h
@@ -17,3 +17,33 @@
 #define PKMAP_NR(virt)	(((virt) - (PKMAP_BASE)) >> PAGE_SHIFT)
 #define PKMAP_ADDR(nr)	(PKMAP_BASE + ((nr) << PAGE_SHIFT))
 #define kmap_prot		PAGE_KERNEL
+
+static inline void flush_cache_kmaps(void)
+{
+	flush_cache_all();
+}
+
+/* Declarations for highmem.c */
+extern unsigned long highstart_pfn, highend_pfn;
+
+extern pte_t *pkmap_page_table;
+
+extern void *kmap_high(struct page *page);
+extern void kunmap_high(struct page *page);
+
+extern void kmap_init(void);
+
+/*
+ * The following functions are already defined by <linux/highmem.h>
+ * when CONFIG_HIGHMEM is not set.
+ */
+#ifdef CONFIG_HIGHMEM
+extern void *kmap(struct page *page);
+extern void kunmap(struct page *page);
+extern void *kmap_atomic(struct page *page);
+extern void __kunmap_atomic(void *kvaddr);
+extern void *kmap_atomic_pfn(unsigned long pfn);
+extern struct page *kmap_atomic_to_page(void *ptr);
+#endif
+
+#endif
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index d9a3769f1f4e..1a774d5a8bbc 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -200,6 +200,11 @@ static inline pgd_t *pgd_offset(const struct mm_struct *mm, unsigned long addr)
 /* Locate an entry in the kernel page global directory */
 #define pgd_offset_k(addr)      pgd_offset(&init_mm, (addr))
 
+#ifdef CONFIG_HIGHMEM
+/* Locate an entry in the second-level page table */
+#define pmd_off_k(addr)  pmd_offset((pud_t *)pgd_offset_k(addr), addr)
+#endif
+
 static inline struct page *pmd_page(pmd_t pmd)
 {
 	return pfn_to_page(pmd_val(pmd) >> _PAGE_PFN_SHIFT);
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index 50b7af58c566..6f9305afc632 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -16,6 +16,7 @@ obj-$(CONFIG_SMP) += tlbflush.o
 endif
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
 obj-$(CONFIG_KASAN)   += kasan_init.o
+obj-$(CONFIG_HIGHMEM) += highmem.o
 
 ifdef CONFIG_KASAN
 KASAN_SANITIZE_kasan_init.o := n
diff --git a/arch/riscv/mm/highmem.c b/arch/riscv/mm/highmem.c
new file mode 100644
index 000000000000..b01ebe34619e
--- /dev/null
+++ b/arch/riscv/mm/highmem.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2005-2020 Andes Technology Corporation
+ */
+
+#include <linux/export.h>
+#include <linux/highmem.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/interrupt.h>
+#include <asm/fixmap.h>
+#include <asm/pgtable.h>
+#include <asm/tlbflush.h>
+
+void *kmap(struct page *page)
+{
+	unsigned long vaddr;
+
+	might_sleep();
+	if (!PageHighMem(page))
+		return page_address(page);
+	vaddr = (unsigned long)kmap_high(page);
+	return (void *)vaddr;
+}
+EXPORT_SYMBOL(kmap);
+
+void kunmap(struct page *page)
+{
+	BUG_ON(in_interrupt());
+	if (!PageHighMem(page))
+		return;
+	kunmap_high(page);
+}
+EXPORT_SYMBOL(kunmap);
+
+void *kmap_atomic(struct page *page)
+{
+	unsigned int idx;
+	unsigned long vaddr;
+	int type;
+	pte_t *ptep;
+
+	preempt_disable();
+	pagefault_disable();
+
+	if (!PageHighMem(page))
+		return page_address(page);
+
+	type = kmap_atomic_idx_push();
+
+	idx = type + KM_TYPE_NR * smp_processor_id();
+	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
+
+	ptep = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
+	set_pte(ptep, mk_pte(page, kmap_prot));
+
+	return (void *)vaddr;
+}
+EXPORT_SYMBOL(kmap_atomic);
+
+void __kunmap_atomic(void *kvaddr)
+{
+	if (kvaddr >= (void *)FIXADDR_START && kvaddr < (void *)FIXADDR_TOP) {
+		unsigned long vaddr = (unsigned long)kvaddr;
+		pte_t *ptep;
+
+		kmap_atomic_idx_pop();
+		ptep = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
+		set_pte(ptep, __pte(0));
+	}
+	pagefault_enable();
+	preempt_enable();
+}
+EXPORT_SYMBOL(__kunmap_atomic);
-- 
2.17.0