| Message ID | 1418110007-13270-1-git-send-email-zhichang.yuan@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 23 January 2015 at 16:21, Catalin Marinas <catalin.marinas@arm.com> wrote: > On Tue, Dec 09, 2014 at 07:26:47AM +0000, zhichang.yuan@linaro.org wrote: >> From: "zhichang.yuan" <zhichang.yuan@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.yuan@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?
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);