On 23 January 2015 at 16:21, Catalin Marinas <catalin.mari...@arm.com> wrote:
> On Tue, Dec 09, 2014 at 07:26:47AM +0000, zhichang.y...@linaro.org wrote:
>> From: "zhichang.yuan" <zhichang.y...@linaro.org>
>>
>> For 64K page system, after mapping a PMD section, the corresponding initial
>> page table is not needed any more. That page can be freed.
>>
>> Changes since v1:
>>
>> * make consistent code between alloc_init_pmd and alloc_init_pud;
>> * flush the TLB before the unused page table is freed;
>>
>> Signed-off-by: Zhichang Yuan <zhichang.y...@linaro.org>
>
> I thought about queuing this patch but I realised that
> alloc_init_pmd/pud may be called in a late context where memblock_free()
> would no longer make sense. Cc'ing Laura and Ard for any ideas here but
> I think we may just end up with a few old page table pages sitting
> around (not many though). In general we don't go from smaller to larger
> mappings (that's what this patch targets) but given the API, I'm not
> sure we have any guarantee.
>
> One solution would be to check for alloc == early_alloc or something
> similar. Cc'ing Laura and Ard as they added the create_mapping_late()
> code.
>
The UEFI page tables are only built up once, based on a series of
disjoint memory regions, so that will never hit either of the
memblock_free() branches.
And AFAICT, the DEBUG_RODATA code does the splitting early, which
causes the create_mapping_late() code to only change permissions, not
change the granularity of any regions.
Perhaps it's sufficient to add a comment and a BUG_ON(alloc !=
early_alloc) to the memblock_free() branches?
--
Ard.
>> ---
>> arch/arm64/include/asm/pgtable.h | 3 +++
>> arch/arm64/mm/mmu.c | 15 ++++++++++++---
>> 2 files changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/pgtable.h
>> b/arch/arm64/include/asm/pgtable.h
>> index 41a43bf..8a135b6 100644
>> --- a/arch/arm64/include/asm/pgtable.h
>> +++ b/arch/arm64/include/asm/pgtable.h
>> @@ -337,9 +337,12 @@ extern pgprot_t phys_mem_access_prot(struct file *file,
>> unsigned long pfn,
>>
>> #ifdef CONFIG_ARM64_64K_PAGES
>> #define pud_sect(pud) (0)
>> +#define pud_table(pud) (1)
>> #else
>> #define pud_sect(pud) ((pud_val(pud) & PUD_TYPE_MASK) == \
>> PUD_TYPE_SECT)
>> +#define pud_table(pud) ((pud_val(pud) & PUD_TYPE_MASK) == \
>> + PUD_TYPE_TABLE)
>> #endif
>>
>> static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index f4f8b50..515f75b 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -191,8 +191,14 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned
>> long addr,
>> * Check for previous table entries created during
>> * boot (__create_page_tables) and flush them.
>> */
>> - if (!pmd_none(old_pmd))
>> + if (!pmd_none(old_pmd)) {
>> flush_tlb_all();
>> + if (pmd_table(old_pmd)) {
>> + phys_addr_t table =
>> __pa(pte_offset_map(&old_pmd, 0));
>> +
>> + memblock_free(table, PAGE_SIZE);
>> + }
>> + }
>> } else {
>> alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
>> prot_pte);
>> @@ -234,9 +240,12 @@ static void __init alloc_init_pud(pgd_t *pgd, unsigned
>> long addr,
>> * Look up the old pmd table and free it.
>> */
>> if (!pud_none(old_pud)) {
>> - phys_addr_t table = __pa(pmd_offset(&old_pud,
>> 0));
>> - memblock_free(table, PAGE_SIZE);
>> flush_tlb_all();
>> + if (pud_table(old_pud)) {
>> + phys_addr_t table =
>> __pa(pmd_offset(&old_pud, 0));
>> +
>> + memblock_free(table, PAGE_SIZE);
>> + }
>> }
>> } else {
>> alloc_init_pmd(pud, addr, next, phys, map_io);
>> --
>> 1.7.9.5
--
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