xtensa: add HIGHMEM support

Introduce fixmap area just below the vmalloc region. Use it for atomic
mapping of high memory pages.
High memory on cores with cache aliasing is not supported and is still
to be implemented. Fail build for such configurations for now.

Signed-off-by: Max Filippov <[e-mail]>

arch/xtensa/Kconfig

···
 
 	  If in doubt, say Y.
 
+config HIGHMEM
+	bool "High Memory Support"
+	help
+	  Linux can use the full amount of RAM in the system by
+	  default. However, the default MMUv2 setup only maps the
+	  lowermost 128 MB of memory linearly to the areas starting
+	  at 0xd0000000 (cached) and 0xd8000000 (uncached).
+	  When there are more than 128 MB memory in the system not
+	  all of it can be "permanently mapped" by the kernel.
+	  The physical memory that's not permanently mapped is called
+	  "high memory".
+
+	  If you are compiling a kernel which will never run on a
+	  machine with more than 128 MB total physical RAM, answer
+	  N here.
+
+	  If unsure, say Y.
+
 endmenu
 
 config XTENSA_CALIBRATE_CCOUNT

arch/xtensa/include/asm/fixmap.h

···
+/*
+ * fixmap.h: compile-time virtual memory allocation
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 1998 Ingo Molnar
+ *
+ * Support of BIGMEM added by Gerhard Wichert, Siemens AG, July 1999
+ */
+
+#ifndef _ASM_FIXMAP_H
+#define _ASM_FIXMAP_H
+
+#include <asm/pgtable.h>
+#ifdef CONFIG_HIGHMEM
+#include <linux/threads.h>
+#include <asm/kmap_types.h>
+#endif
+
+/*
+ * Here we define all the compile-time 'special' virtual
+ * addresses. The point is to have a constant address at
+ * compile time, but to set the physical address only
+ * in the boot process. We allocate these special  addresses
+ * from the end of the consistent memory region backwards.
+ * Also this lets us do fail-safe vmalloc(), we
+ * can guarantee that these special addresses and
+ * vmalloc()-ed addresses never overlap.
+ *
+ * these 'compile-time allocated' memory buffers are
+ * fixed-size 4k pages. (or larger if used with an increment
+ * higher than 1) use fixmap_set(idx,phys) to associate
+ * physical memory with fixmap indices.
+ */
+enum fixed_addresses {
+#ifdef CONFIG_HIGHMEM
+	/* reserved pte's for temporary kernel mappings */
+	FIX_KMAP_BEGIN,
+	FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS) - 1,
+#endif
+	__end_of_fixed_addresses
+};
+
+#define FIXADDR_TOP     (VMALLOC_START - PAGE_SIZE)
+#define FIXADDR_SIZE	(__end_of_fixed_addresses << PAGE_SHIFT)
+#define FIXADDR_START	((FIXADDR_TOP - FIXADDR_SIZE) & PMD_MASK)
+
+#include <asm-generic/fixmap.h>
+
+#define kmap_get_fixmap_pte(vaddr) \
+	pte_offset_kernel( \
+		pmd_offset(pud_offset(pgd_offset_k(vaddr), (vaddr)), (vaddr)), \
+		(vaddr) \
+	)
+
+#endif

arch/xtensa/include/asm/highmem.h

···
  * this archive for more details.
  *
  * Copyright (C) 2003 - 2005 Tensilica Inc.
+ * Copyright (C) 2014 Cadence Design Systems Inc.
  */
 
 #ifndef _XTENSA_HIGHMEM_H
 #define _XTENSA_HIGHMEM_H
 
-extern void flush_cache_kmaps(void);
+#include <asm/cacheflush.h>
+#include <asm/fixmap.h>
+#include <asm/kmap_types.h>
+#include <asm/pgtable.h>
+
+#define PKMAP_BASE		(FIXADDR_START - PMD_SIZE)
+#define LAST_PKMAP		PTRS_PER_PTE
+#define LAST_PKMAP_MASK		(LAST_PKMAP - 1)
+#define PKMAP_NR(virt)		(((virt) - PKMAP_BASE) >> PAGE_SHIFT)
+#define PKMAP_ADDR(nr)		(PKMAP_BASE + ((nr) << PAGE_SHIFT))
+
+#define kmap_prot		PAGE_KERNEL
+
+extern pte_t *pkmap_page_table;
+
+void *kmap_high(struct page *page);
+void kunmap_high(struct page *page);
+
+static inline void *kmap(struct page *page)
+{
+	BUG_ON(in_interrupt());
+	if (!PageHighMem(page))
+		return page_address(page);
+	return kmap_high(page);
+}
+
+static inline void kunmap(struct page *page)
+{
+	BUG_ON(in_interrupt());
+	if (!PageHighMem(page))
+		return;
+	kunmap_high(page);
+}
+
+static inline void flush_cache_kmaps(void)
+{
+	flush_cache_all();
+}
+
+void *kmap_atomic(struct page *page);
+void __kunmap_atomic(void *kvaddr);
+
+void kmap_init(void);
 
 #endif

arch/xtensa/include/asm/pgtable.h

···
 	update_pte(ptep, pteval);
 }
 
+static inline void set_pte(pte_t *ptep, pte_t pteval)
+{
+	update_pte(ptep, pteval);
+}
 
 static inline void
 set_pmd(pmd_t *pmdp, pmd_t pmdval)

arch/xtensa/mm/Makefile

···
 
 obj-y			:= init.o cache.o misc.o
 obj-$(CONFIG_MMU)	+= fault.o mmu.o tlb.o
+obj-$(CONFIG_HIGHMEM)	+= highmem.o

arch/xtensa/mm/cache.c

···
  *
  */
 
+#if (DCACHE_WAY_SIZE > PAGE_SIZE) && defined(CONFIG_HIGHMEM)
+#error "HIGHMEM is not supported on cores with aliasing cache."
+#endif
+
 #if (DCACHE_WAY_SIZE > PAGE_SIZE) && XCHAL_DCACHE_IS_WRITEBACK
 
 /*
···
 #else
 	if (!PageReserved(page) && !test_bit(PG_arch_1, &page->flags)
 	    && (vma->vm_flags & VM_EXEC) != 0) {
-	    	unsigned long paddr = (unsigned long) page_address(page);
+		unsigned long paddr = (unsigned long)kmap_atomic(page);
 		__flush_dcache_page(paddr);
 		__invalidate_icache_page(paddr);
 		set_bit(PG_arch_1, &page->flags);
+		kunmap_atomic((void *)paddr);
 	}
 #endif
 }

arch/xtensa/mm/highmem.c

···
+/*
+ * High memory support for Xtensa architecture
+ *
+ * This file is subject to the terms and conditions of the GNU General
+ * Public License.  See the file "COPYING" in the main directory of
+ * this archive for more details.
+ *
+ * Copyright (C) 2014 Cadence Design Systems Inc.
+ */
+
+#include <linux/export.h>
+#include <linux/highmem.h>
+#include <asm/tlbflush.h>
+
+static pte_t *kmap_pte;
+
+void *kmap_atomic(struct page *page)
+{
+	enum fixed_addresses idx;
+	unsigned long vaddr;
+	int type;
+
+	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);
+#ifdef CONFIG_DEBUG_HIGHMEM
+	BUG_ON(!pte_none(*(kmap_pte - idx)));
+#endif
+	set_pte(kmap_pte - idx, mk_pte(page, PAGE_KERNEL_EXEC));
+
+	return (void *)vaddr;
+}
+EXPORT_SYMBOL(kmap_atomic);
+
+void __kunmap_atomic(void *kvaddr)
+{
+	int idx, type;
+
+	if (kvaddr >= (void *)FIXADDR_START &&
+	    kvaddr < (void *)FIXADDR_TOP) {
+		type = kmap_atomic_idx();
+		idx = type + KM_TYPE_NR * smp_processor_id();
+
+		/*
+		 * Force other mappings to Oops if they'll try to access this
+		 * pte without first remap it.  Keeping stale mappings around
+		 * is a bad idea also, in case the page changes cacheability
+		 * attributes or becomes a protected page in a hypervisor.
+		 */
+		pte_clear(&init_mm, kvaddr, kmap_pte - idx);
+		local_flush_tlb_kernel_range((unsigned long)kvaddr,
+					     (unsigned long)kvaddr + PAGE_SIZE);
+
+		kmap_atomic_idx_pop();
+	}
+
+	pagefault_enable();
+}
+EXPORT_SYMBOL(__kunmap_atomic);
+
+void __init kmap_init(void)
+{
+	unsigned long kmap_vstart;
+
+	/* cache the first kmap pte */
+	kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);
+	kmap_pte = kmap_get_fixmap_pte(kmap_vstart);
+}

arch/xtensa/mm/init.c

···
 #include <linux/errno.h>
 #include <linux/bootmem.h>
 #include <linux/gfp.h>
+#include <linux/highmem.h>
 #include <linux/swap.h>
 #include <linux/mman.h>
 #include <linux/nodemask.h>
···
 
 void __init zones_init(void)
 {
-	unsigned long zones_size[MAX_NR_ZONES];
-	int i;
-
 	/* All pages are DMA-able, so we put them all in the DMA zone. */
-
-	zones_size[ZONE_DMA] = max_low_pfn - ARCH_PFN_OFFSET;
-	for (i = 1; i < MAX_NR_ZONES; i++)
-		zones_size[i] = 0;
-
+	unsigned long zones_size[MAX_NR_ZONES] = {
+		[ZONE_DMA] = max_low_pfn - ARCH_PFN_OFFSET,
 #ifdef CONFIG_HIGHMEM
-	zones_size[ZONE_HIGHMEM] = max_pfn - max_low_pfn;
+		[ZONE_HIGHMEM] = max_pfn - max_low_pfn,
 #endif
-
+	};
 	free_area_init_node(0, zones_size, ARCH_PFN_OFFSET, NULL);
 }
 
···
 
 void __init mem_init(void)
 {
-	max_mapnr = max_low_pfn - ARCH_PFN_OFFSET;
-	high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
-
 #ifdef CONFIG_HIGHMEM
-#error HIGHGMEM not implemented in init.c
+	unsigned long tmp;
+
+	reset_all_zones_managed_pages();
+	for (tmp = max_low_pfn; tmp < max_pfn; tmp++)
+		free_highmem_page(pfn_to_page(tmp));
 #endif
+
+	max_mapnr = max_pfn - ARCH_PFN_OFFSET;
+	high_memory = (void *)__va(max_low_pfn << PAGE_SHIFT);
 
 	free_all_bootmem();
 
 	mem_init_print_info(NULL);
+	pr_info("virtual kernel memory layout:\n"
+#ifdef CONFIG_HIGHMEM
+		"    pkmap   : 0x%08lx - 0x%08lx  (%5lu kB)\n"
+		"    fixmap  : 0x%08lx - 0x%08lx  (%5lu kB)\n"
+#endif
+		"    vmalloc : 0x%08x - 0x%08x  (%5u MB)\n"
+		"    lowmem  : 0x%08x - 0x%08lx  (%5lu MB)\n",
+#ifdef CONFIG_HIGHMEM
+		PKMAP_BASE, PKMAP_BASE + LAST_PKMAP * PAGE_SIZE,
+		(LAST_PKMAP*PAGE_SIZE) >> 10,
+		FIXADDR_START, FIXADDR_TOP,
+		(FIXADDR_TOP - FIXADDR_START) >> 10,
+#endif
+		VMALLOC_START, VMALLOC_END,
+		(VMALLOC_END - VMALLOC_START) >> 20,
+		PAGE_OFFSET, PAGE_OFFSET +
+		(max_low_pfn - min_low_pfn) * PAGE_SIZE,
+		((max_low_pfn - min_low_pfn) * PAGE_SIZE) >> 20);
 }
 
 #ifdef CONFIG_BLK_DEV_INITRD

arch/xtensa/mm/mmu.c

···
  *
  * Extracted from init.c
  */
+#include <linux/bootmem.h>
 #include <linux/percpu.h>
 #include <linux/init.h>
 #include <linux/string.h>
···
 #include <asm/initialize_mmu.h>
 #include <asm/io.h>
 
+#if defined(CONFIG_HIGHMEM)
+static void * __init init_pmd(unsigned long vaddr)
+{
+	pgd_t *pgd = pgd_offset_k(vaddr);
+	pmd_t *pmd = pmd_offset(pgd, vaddr);
+
+	if (pmd_none(*pmd)) {
+		unsigned i;
+		pte_t *pte = alloc_bootmem_low_pages(PAGE_SIZE);
+
+		for (i = 0; i < 1024; i++)
+			pte_clear(NULL, 0, pte + i);
+
+		set_pmd(pmd, __pmd(((unsigned long)pte) & PAGE_MASK));
+		BUG_ON(pte != pte_offset_kernel(pmd, 0));
+		pr_debug("%s: vaddr: 0x%08lx, pmd: 0x%p, pte: 0x%p\n",
+			 __func__, vaddr, pmd, pte);
+		return pte;
+	} else {
+		return pte_offset_kernel(pmd, 0);
+	}
+}
+
+static void __init fixedrange_init(void)
+{
+	BUILD_BUG_ON(FIXADDR_SIZE > PMD_SIZE);
+	init_pmd(__fix_to_virt(__end_of_fixed_addresses - 1) & PMD_MASK);
+}
+#endif
+
 void __init paging_init(void)
 {
 	memset(swapper_pg_dir, 0, PAGE_SIZE);
+#ifdef CONFIG_HIGHMEM
+	fixedrange_init();
+	pkmap_page_table = init_pmd(PKMAP_BASE);
+	kmap_init();
+#endif
 }
 
 /*