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Subject[PATCH v5] ARM: early fixmap support for earlycon
Date
Add early fixmap support, initially to support permanent, fixed
mapping support for early console. A temporary, early pte is
created which is migrated to a permanent mapping in paging_init.
This is also needed since the attributes may change as the memory
types are initialized. The 3MiB range of fixmap spans two pte
tables, but currently only one pte is created for early fixmap
support.

Re-add FIX_KMAP_BEGIN to the index calculation in highmem.c since
the index for kmap does not start at zero anymore. This reverts
4221e2e6b316 ("ARM: 8031/1: fixmap: remove FIX_KMAP_BEGIN and
FIX_KMAP_END") to some extent.

Cc: Mark Salter <msalter@redhat.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Kees Cook <keescook@chromium.org>
Cc: Laura Abbott <lauraa@codeaurora.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stefan Agner <stefan@agner.ch>
---
Hi Russel,

All three compile issues were related to MMU/!MMU differences. The solution
is rather simple: This patch now only configures FIX_EARLYCON_MEM if the
MMU is available. This makes sense since on !MMU platform we can use ioremap
very early...

--
Stefan

Changes since v4:
- Add MMU dependency for FIX_EARLYCON_MEM
- Call early_fixmap_init conditionally, only if FIX_EARLYCON_MEM is set

Changes since v3:
- Remove address of on functions
- Clear all pmd's except early fixmap pmd in devicemaps_init
- Update comment in devicemaps_init since earlycon works now as debug method
- Add comment regarding FIXMAP_PAGE_IO/FIXMAP_PAGE_NOCACHE use

Changes since v2:
- Rebased and tested on rmk/for-next
- Flush TLB's when clearing the temporary PMD in early_fixmap_shutdown

Changes since v1 (RFC):
- Rebased and tested on v3.19-rc5
- Spelling errors in comments and commit message
- Added Rob's SOB

arch/arm/Kconfig | 3 ++
arch/arm/include/asm/fixmap.h | 15 +++++++-
arch/arm/kernel/setup.c | 4 ++
arch/arm/mm/highmem.c | 6 +--
arch/arm/mm/mmu.c | 88 +++++++++++++++++++++++++++++++++++++++----
5 files changed, 105 insertions(+), 11 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index a750c14..1bcda7c 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -188,6 +188,9 @@ config ARCH_HAS_ILOG2_U64
config ARCH_HAS_BANDGAP
bool

+config FIX_EARLYCON_MEM
+ def_bool y if MMU
+
config GENERIC_HWEIGHT
bool
default y
diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
index 0415eae..58cfe9f 100644
--- a/arch/arm/include/asm/fixmap.h
+++ b/arch/arm/include/asm/fixmap.h
@@ -6,9 +6,13 @@
#define FIXADDR_TOP (FIXADDR_END - PAGE_SIZE)

#include <asm/kmap_types.h>
+#include <asm/pgtable.h>

enum fixed_addresses {
- FIX_KMAP_BEGIN,
+ FIX_EARLYCON_MEM_BASE,
+ __end_of_permanent_fixed_addresses,
+
+ FIX_KMAP_BEGIN = __end_of_permanent_fixed_addresses,
FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS) - 1,

/* Support writing RO kernel text via kprobes, jump labels, etc. */
@@ -18,7 +22,16 @@ 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)
+
+/* Used by set_fixmap_(io|nocache), both meant for mapping a device */
+#define FIXMAP_PAGE_IO (FIXMAP_PAGE_COMMON | L_PTE_MT_DEV_SHARED | L_PTE_SHARED)
+#define FIXMAP_PAGE_NOCACHE FIXMAP_PAGE_IO
+
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>

diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 36c18b7..b3b7831 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -37,6 +37,7 @@
#include <asm/cpu.h>
#include <asm/cputype.h>
#include <asm/elf.h>
+#include <asm/fixmap.h>
#include <asm/procinfo.h>
#include <asm/psci.h>
#include <asm/sections.h>
@@ -954,6 +955,9 @@ void __init setup_arch(char **cmdline_p)
strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE);
*cmdline_p = cmd_line;

+ if (IS_ENABLED(CONFIG_FIX_EARLYCON_MEM))
+ early_fixmap_init();
+
parse_early_param();

#ifdef CONFIG_MMU
diff --git a/arch/arm/mm/highmem.c b/arch/arm/mm/highmem.c
index ee8dfa7..9df5f09 100644
--- a/arch/arm/mm/highmem.c
+++ b/arch/arm/mm/highmem.c
@@ -79,7 +79,7 @@ void *kmap_atomic(struct page *page)

type = kmap_atomic_idx_push();

- idx = type + KM_TYPE_NR * smp_processor_id();
+ idx = FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();
vaddr = __fix_to_virt(idx);
#ifdef CONFIG_DEBUG_HIGHMEM
/*
@@ -106,7 +106,7 @@ void __kunmap_atomic(void *kvaddr)

if (kvaddr >= (void *)FIXADDR_START) {
type = kmap_atomic_idx();
- idx = type + KM_TYPE_NR * smp_processor_id();
+ idx = FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();

if (cache_is_vivt())
__cpuc_flush_dcache_area((void *)vaddr, PAGE_SIZE);
@@ -138,7 +138,7 @@ void *kmap_atomic_pfn(unsigned long pfn)
return page_address(page);

type = kmap_atomic_idx_push();
- idx = type + KM_TYPE_NR * smp_processor_id();
+ idx = FIX_KMAP_BEGIN + type + KM_TYPE_NR * smp_processor_id();
vaddr = __fix_to_virt(idx);
#ifdef CONFIG_DEBUG_HIGHMEM
BUG_ON(!pte_none(get_fixmap_pte(vaddr)));
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 6ca7d9a..fb9e817 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -357,6 +357,47 @@ const struct mem_type *get_mem_type(unsigned int type)
}
EXPORT_SYMBOL(get_mem_type);

+static pte_t *(*pte_offset_fixmap)(pmd_t *dir, unsigned long addr);
+
+static pte_t bm_pte[PTRS_PER_PTE + PTE_HWTABLE_PTRS]
+ __aligned(PTE_HWTABLE_OFF + PTE_HWTABLE_SIZE) __initdata;
+
+static pte_t * __init pte_offset_early_fixmap(pmd_t *dir, unsigned long addr)
+{
+ return &bm_pte[pte_index(addr)];
+}
+
+static pte_t *pte_offset_late_fixmap(pmd_t *dir, unsigned long addr)
+{
+ return pte_offset_kernel(dir, addr);
+}
+
+static inline pmd_t * __init fixmap_pmd(unsigned long addr)
+{
+ pgd_t *pgd = pgd_offset_k(addr);
+ pud_t *pud = pud_offset(pgd, addr);
+ pmd_t *pmd = pmd_offset(pud, addr);
+
+ return pmd;
+}
+
+void __init early_fixmap_init(void)
+{
+ pmd_t *pmd;
+
+ /*
+ * The early fixmap range spans multiple pmds, for which
+ * we are not prepared:
+ */
+ BUILD_BUG_ON((__fix_to_virt(__end_of_permanent_fixed_addresses) >> PMD_SHIFT)
+ != FIXADDR_TOP >> PMD_SHIFT);
+
+ pmd = fixmap_pmd(FIXADDR_TOP);
+ pmd_populate_kernel(&init_mm, pmd, bm_pte);
+
+ pte_offset_fixmap = pte_offset_early_fixmap;
+}
+
/*
* To avoid TLB flush broadcasts, this uses local_flush_tlb_kernel_range().
* As a result, this can only be called with preemption disabled, as under
@@ -365,7 +406,7 @@ EXPORT_SYMBOL(get_mem_type);
void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot)
{
unsigned long vaddr = __fix_to_virt(idx);
- pte_t *pte = pte_offset_kernel(pmd_off_k(vaddr), vaddr);
+ pte_t *pte = pte_offset_fixmap(pmd_off_k(vaddr), vaddr);

/* Make sure fixmap region does not exceed available allocation. */
BUILD_BUG_ON(FIXADDR_START + (__end_of_fixed_addresses * PAGE_SIZE) >
@@ -855,7 +896,7 @@ static void __init create_mapping(struct map_desc *md)
}

if ((md->type == MT_DEVICE || md->type == MT_ROM) &&
- md->virtual >= PAGE_OFFSET &&
+ md->virtual >= PAGE_OFFSET && md->virtual < FIXADDR_START &&
(md->virtual < VMALLOC_START || md->virtual >= VMALLOC_END)) {
pr_warn("BUG: mapping for 0x%08llx at 0x%08lx out of vmalloc space\n",
(long long)__pfn_to_phys((u64)md->pfn), md->virtual);
@@ -1213,10 +1254,10 @@ void __init arm_mm_memblock_reserve(void)

/*
* Set up the device mappings. Since we clear out the page tables for all
- * mappings above VMALLOC_START, we will remove any debug device mappings.
- * This means you have to be careful how you debug this function, or any
- * called function. This means you can't use any function or debugging
- * method which may touch any device, otherwise the kernel _will_ crash.
+ * mappings above VMALLOC_START, except early fixmap, we might remove debug
+ * device mappings. This means earlycon can be used to debug this function
+ * Any other function or debugging method which may touch any device _will_
+ * crash the kernel.
*/
static void __init devicemaps_init(const struct machine_desc *mdesc)
{
@@ -1231,7 +1272,10 @@ static void __init devicemaps_init(const struct machine_desc *mdesc)

early_trap_init(vectors);

- for (addr = VMALLOC_START; addr; addr += PMD_SIZE)
+ /*
+ * Clear page table except top pmd used by early fixmaps
+ */
+ for (addr = VMALLOC_START; addr < (FIXADDR_TOP & PMD_MASK); addr += PMD_SIZE)
pmd_clear(pmd_off_k(addr));

/*
@@ -1483,6 +1527,35 @@ void __init early_paging_init(const struct machine_desc *mdesc)

#endif

+static void __init early_fixmap_shutdown(void)
+{
+ int i;
+ unsigned long va = fix_to_virt(__end_of_permanent_fixed_addresses - 1);
+
+ pte_offset_fixmap = pte_offset_late_fixmap;
+ pmd_clear(fixmap_pmd(va));
+ local_flush_tlb_kernel_page(va);
+
+ for (i = 0; i < __end_of_permanent_fixed_addresses; i++) {
+ pte_t *pte;
+ struct map_desc map;
+
+ map.virtual = fix_to_virt(i);
+ pte = pte_offset_early_fixmap(pmd_off_k(map.virtual), map.virtual);
+
+ /* Only i/o device mappings are supported ATM */
+ if (pte_none(*pte) ||
+ (pte_val(*pte) & L_PTE_MT_MASK) != L_PTE_MT_DEV_SHARED)
+ continue;
+
+ map.pfn = pte_pfn(*pte);
+ map.type = MT_DEVICE;
+ map.length = PAGE_SIZE;
+
+ create_mapping(&map);
+ }
+}
+
/*
* paging_init() sets up the page tables, initialises the zone memory
* maps, and sets up the zero page, bad page and bad page tables.
@@ -1495,6 +1568,7 @@ void __init paging_init(const struct machine_desc *mdesc)
prepare_page_table();
map_lowmem();
dma_contiguous_remap();
+ early_fixmap_shutdown();
devicemaps_init(mdesc);
kmap_init();
tcm_init();
--
2.5.0


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