[PATCH v2] arm: Fix memory attribute inconsistencies when using fixmap

[Jon Medhurst]

To cope with the variety in ARM architectures and configurations, the
pagetable attributes for kernel memory are generated at runtime to match
the system the kernel finds itself on. This calculated value is stored
in pgprot_kernel.

However, when early fixmap support was added for arm (commit
a5f4c561b3b1) the attributes used for mappings were hard coded because
pgprot_kernel is not set up early enough. Unfortunately, when fixmap is
used after early boot this means the memory being mapped can have
different attributes to existing mappings, potentially leading to
unpredictable behaviour. A specific problem also exists due to the hard
coded values not include the 'shareable' attribute which means on
systems where this matters (e.g. those with multiple CPU clusters) the
cache contents for a memory location can become inconsistent between
CPUs.

To resolve these issues we change fixmap to use the same memory
attributes (from pgprot_kernel) that the rest of the kernel uses. To
enable this we need to refactor the initialisation code so
build_mem_type_table is called early enough. Note, that relies on early
param parsing for memory type overrides passed via the kernel command
line, so we need to make sure this call is still after
parse_early_params().

Fixes: a5f4c561b3b1 ("ARM: 8415/1: early fixmap support for earlycon")
Cc: stable at vger.kernel.org # v4.3+
---

Changes since v1:
- Completely rewritten based on Russell's and Ard's sugestions
- Subject changed from "arm: Fix cache inconsistency when using fixmap"


 arch/arm/include/asm/fixmap.h |  7 +------
 arch/arm/include/asm/mmu.h    |  2 ++
 arch/arm/kernel/setup.c       |  5 +----
 arch/arm/mm/mmu.c             | 12 ++++++++++--
 4 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index 5c17d2dec777..c54f06ace2a1 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -41,7 +41,7 @@ static const enum fixed_addresses __end_of_fixed_addresses =
 
 #define FIXMAP_PAGE_COMMON	(L_PTE_YOUNG | L_PTE_PRESENT | L_PTE_XN | L_PTE_DIRTY)
 
-#define FIXMAP_PAGE_NORMAL	(FIXMAP_PAGE_COMMON | L_PTE_MT_WRITEBACK)
+#define FIXMAP_PAGE_NORMAL	(pgprot_kernel | L_PTE_XN)
 #define FIXMAP_PAGE_RO		(FIXMAP_PAGE_NORMAL | L_PTE_RDONLY)
 
 /* Used by set_fixmap_(io|nocache), both meant for mapping a device */
@@ -53,13 +53,8 @@ static const enum fixed_addresses __end_of_fixed_addresses =
 #ifdef CONFIG_MMU
 
 void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot);
-void __init early_fixmap_init(void);
 
 #include <asm-generic/fixmap.h>
 
-#else
-
-static inline void early_fixmap_init(void) { }
-
 #endif
 #endif
diff --git a/arch/arm/include/asm/mmu.h b/arch/arm/include/asm/mmu.h
index a5b47421059d..920d29ca5c3b 100644
--- a/arch/arm/include/asm/mmu.h
+++ b/arch/arm/include/asm/mmu.h
@@ -24,6 +24,8 @@ typedef struct {
 #define ASID(mm)	(0)
 #endif
 
+void early_mm_init(void);
+
 #else
 
 /*
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index f4e54503afa9..37c59589aac3 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -40,7 +40,6 @@
 #include <asm/efi.h>
 #include <asm/elf.h>
 #include <asm/early_ioremap.h>
-#include <asm/fixmap.h>
 #include <asm/procinfo.h>
 #include <asm/psci.h>
 #include <asm/sections.h>
@@ -1082,12 +1081,10 @@ void __init setup_arch(char **cmdline_p)
 	strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
 	*cmdline_p = cmd_line;
 
-	early_fixmap_init();
-	early_ioremap_init();
-
 	parse_early_param();
 
 #ifdef CONFIG_MMU
+	early_mm_init();
 	early_paging_init(mdesc);
 #endif
 	setup_dma_zone(mdesc);
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 4e016d7f37b3..f81809e6bd10 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -22,6 +22,7 @@
 #include <asm/cputype.h>
 #include <asm/sections.h>
 #include <asm/cachetype.h>
+#include <asm/early_ioremap.h>
 #include <asm/fixmap.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
@@ -382,7 +383,7 @@ static inline pmd_t * __init fixmap_pmd(unsigned long addr)
 	return pmd;
 }
 
-void __init early_fixmap_init(void)
+static void __init early_fixmap_init(void)
 {
 	pmd_t *pmd;
 
@@ -1616,7 +1617,6 @@ void __init paging_init(const struct machine_desc *mdesc)
 {
 	void *zero_page;
 
-	build_mem_type_table();
 	prepare_page_table();
 	map_lowmem();
 	memblock_set_current_limit(arm_lowmem_limit);
@@ -1636,3 +1636,11 @@ void __init paging_init(const struct machine_desc *mdesc)
 	empty_zero_page = virt_to_page(zero_page);
 	__flush_dcache_page(NULL, empty_zero_page);
 }
+
+void __init early_mm_init(void)
+{
+	build_mem_type_table();
+
+	early_fixmap_init();
+	early_ioremap_init();
+}
-- 
2.11.0