[ARM] kmap support

The kmap virtual area borrows a 2MB range at the top of the 16MB area
below PAGE_OFFSET currently reserved for kernel modules and/or the
XIP kernel.  This 2MB corresponds to the range covered by 2 consecutive
second-level page tables, or a single pmd entry as seen by the Linux
page table abstraction.  Because XIP kernels are unlikely to be seen
on systems needing highmem support, there shouldn't be any shortage of
VM space for modules (14 MB for modules is still way more than twice the
typical usage).

Because the virtual mapping of highmem pages can go away at any moment
after kunmap() is called on them, we need to bypass the delayed cache
flushing provided by flush_dcache_page() in that case.

The atomic kmap versions are based on fixmaps, and
__cpuc_flush_dcache_page() is used directly in that case.

Signed-off-by: Nicolas Pitre <nico@marvell.com>

1 files changed, 116 insertions, 0 deletions

diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
new file mode 100644
index 000000000000..a34954d9df7d
--- /dev/null
+++ b/arch/arm/mm/highmem.c
@@ -0,0 +1,116 @@
+/*
+ * arch/arm/mm/highmem.c -- ARM highmem support
+ *
+ * Author:	Nicolas Pitre
+ * Created:	september 8, 2008
+ * Copyright:	Marvell Semiconductors Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/highmem.h>
+#include <linux/interrupt.h>
+#include <asm/fixmap.h>
+#include <asm/cacheflush.h>
+#include <asm/tlbflush.h>
+#include "mm.h"
+
+void *kmap(struct page *page)
+{
+	might_sleep();
+	if (!PageHighMem(page))
+		return page_address(page);
+	return kmap_high(page);
+}
+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, enum km_type type)
+{
+	unsigned int idx;
+	unsigned long vaddr;
+
+	pagefault_disable();
+	if (!PageHighMem(page))
+		return page_address(page);
+
+	idx = type + KM_TYPE_NR * smp_processor_id();
+	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
+#ifdef CONFIG_DEBUG_HIGHMEM
+	/*
+	 * With debugging enabled, kunmap_atomic forces that entry to 0.
+	 * Make sure it was indeed properly unmapped.
+	 */
+	BUG_ON(!pte_none(*(TOP_PTE(vaddr))));
+#endif
+	set_pte_ext(TOP_PTE(vaddr), mk_pte(page, kmap_prot), 0);
+	/*
+	 * When debugging is off, kunmap_atomic leaves the previous mapping
+	 * in place, so this TLB flush ensures the TLB is updated with the
+	 * new mapping.
+	 */
+	local_flush_tlb_kernel_page(vaddr);
+
+	return (void *)vaddr;
+}
+EXPORT_SYMBOL(kmap_atomic);
+
+void kunmap_atomic(void *kvaddr, enum km_type type)
+{
+	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
+	unsigned int idx = type + KM_TYPE_NR * smp_processor_id();
+
+	if (kvaddr >= (void *)FIXADDR_START) {
+		__cpuc_flush_dcache_page((void *)vaddr);
+#ifdef CONFIG_DEBUG_HIGHMEM
+		BUG_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));
+		set_pte_ext(TOP_PTE(vaddr), __pte(0), 0);
+		local_flush_tlb_kernel_page(vaddr);
+#else
+		(void) idx;  /* to kill a warning */
+#endif
+	}
+	pagefault_enable();
+}
+EXPORT_SYMBOL(kunmap_atomic);
+
+void *kmap_atomic_pfn(unsigned long pfn, enum km_type type)
+{
+	unsigned int idx;
+	unsigned long vaddr;
+
+	pagefault_disable();
+
+	idx = type + KM_TYPE_NR * smp_processor_id();
+	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
+#ifdef CONFIG_DEBUG_HIGHMEM
+	BUG_ON(!pte_none(*(TOP_PTE(vaddr))));
+#endif
+	set_pte_ext(TOP_PTE(vaddr), pfn_pte(pfn, kmap_prot), 0);
+	local_flush_tlb_kernel_page(vaddr);
+
+	return (void *)vaddr;
+}
+
+struct page *kmap_atomic_to_page(const void *ptr)
+{
+	unsigned long vaddr = (unsigned long)ptr;
+	pte_t *pte;
+
+	if (vaddr < FIXADDR_START)
+		return virt_to_page(ptr);
+
+	pte = TOP_PTE(vaddr);
+	return pte_page(*pte);
+}