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arm: Allow remapping lowmem as 4K pages

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Lowmem is currently mapped with sections (1MB/2MB) whenever
possible due to TLB performance boosts. Sections cannot easily
be changed at runtime however which makes implementing certain
features annoying. Add an option to map lowmem with 4K patches.
This is intended to be used as a debugging feature and should
NOT be used for performance testing.

Change-Id: I9612a99b8e05a022f5ba7e568f21307cf66b5667
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
This commit is contained in:
Laura Abbott 2014-04-14 19:42:04 -07:00
parent 5698cb804e
commit 853075183f
2 changed files with 112 additions and 4 deletions
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11
arch/arm/Kconfig.debug
View file

@ -75,6 +75,17 @@ config DEBUG_USER
8 - SIGSEGV faults
16 - SIGBUS faults
config FORCE_PAGES
bool "Force lowmem to be mapped with 4K pages"
help
There are some advanced debug features that can only be done when
memory is mapped with pages instead of sections. Enable this option
to always map lowmem pages with pages. This may have a performance
cost due to increased TLB pressure.
If unsure say N.
# These options are only for real kernel hackers who want to get their hands dirty.
config DEBUG_LL
bool "Kernel low-level debugging functions (read help!)"

105
arch/arm/mm/mmu.c
View file

@ -393,11 +393,13 @@ int set_memory_##_name(unsigned long addr, int numpages) \
unsigned long size = PAGE_SIZE*numpages; \
unsigned end = start + size; \
\
if (start < MODULES_VADDR || start >= MODULES_END) \
return -EINVAL;\
if (!IS_ENABLED(CONFIG_FORCE_PAGES)) { \
if (start < MODULES_VADDR || start >= MODULES_END) \
return -EINVAL;\
\
if (end < MODULES_VADDR || end >= MODULES_END) \
return -EINVAL; \
if (end < MODULES_VADDR || end >= MODULES_END) \
return -EINVAL; \
} \
\
apply_to_page_range(&init_mm, start, size, callback, NULL); \
flush_tlb_kernel_range(start, end); \
@ -1567,6 +1569,100 @@ static void __init map_lowmem(void)
}
}
#ifdef CONFIG_FORCE_PAGES
/*
* remap a PMD into pages
* We split a single pmd here none of this two pmd nonsense
*/
static noinline void split_pmd(pmd_t *pmd, unsigned long addr,
unsigned long end, unsigned long pfn,
const struct mem_type *type)
{
pte_t *pte, *start_pte;
start_pte = early_alloc(PTE_HWTABLE_OFF + PTE_HWTABLE_SIZE);
pte = start_pte;
do {
set_pte_ext(pte, pfn_pte(pfn, type->prot_pte), 0);
pfn++;
} while (pte++, addr += PAGE_SIZE, addr != end);
*pmd = __pmd((__pa(start_pte) + PTE_HWTABLE_OFF) | type->prot_l1);
mb();
flush_pmd_entry(pmd);
flush_tlb_all();
}
/*
* It's significantly easier to remap as pages later after all memory is
* mapped. Everything is sections so all we have to do is split
*/
static void __init remap_pages(void)
{
struct memblock_region *reg;
for_each_memblock(memory, reg) {
phys_addr_t phys_start = reg->base;
phys_addr_t phys_end = reg->base + reg->size;
unsigned long addr = (unsigned long)__va(phys_start);
unsigned long end = (unsigned long)__va(phys_end);
pmd_t *pmd = NULL;
unsigned long next;
unsigned long pfn = __phys_to_pfn(phys_start);
bool fixup = false;
unsigned long saved_start = addr;
if (phys_end > arm_lowmem_limit)
end = (unsigned long)__va(arm_lowmem_limit);
if (phys_start >= phys_end)
break;
pmd = pmd_offset(
pud_offset(pgd_offset(&init_mm, addr), addr), addr);
#ifndef CONFIG_ARM_LPAE
if (addr & SECTION_SIZE) {
fixup = true;
pmd_empty_section_gap((addr - SECTION_SIZE) & PMD_MASK);
pmd++;
}
if (end & SECTION_SIZE)
pmd_empty_section_gap(end);
#endif
do {
next = addr + SECTION_SIZE;
if (pmd_none(*pmd) || pmd_bad(*pmd))
split_pmd(pmd, addr, next, pfn,
&mem_types[MT_MEMORY]);
pmd++;
pfn += SECTION_SIZE >> PAGE_SHIFT;
} while (addr = next, addr < end);
if (fixup) {
/*
* Put a faulting page table here to avoid detecting no
* pmd when accessing an odd section boundary. This
* needs to be faulting to help catch errors and avoid
* speculation
*/
pmd = pmd_off_k(saved_start);
pmd[0] = pmd[1] & ~1;
}
}
}
#else
static void __init remap_pages(void)
{
}
#endif
/*
* paging_init() sets up the page tables, initialises the zone memory
* maps, and sets up the zero page, bad page and bad page tables.
@ -1581,6 +1677,7 @@ void __init paging_init(struct machine_desc *mdesc)
prepare_page_table();
map_lowmem();
dma_contiguous_remap();
remap_pages();
devicemaps_init(mdesc);
kmap_init();
tcm_init();