Subject: [PATCH v0] ARMv8:mm:Support the DEBUG_PAGEALLOC

From: [email-masked] (zhichang.yuan)
Date: Tue, 28 Oct 2014 14:11:22 +0800

Hi, Laura,

Thanks for your comments!

On 2014?10?28? 06:25, Laura Abbott wrote:
> Hi,
>
> On 10/26/2014 9:01 PM, zhichang.yuan at linaro.org wrote:
>> From: "zhichang.yuan" <[email-masked]>
>>
>> This patch targets to support DEBUG_PAGEALLOC on ARMv8.
>>
>> Meanwhile, it adds the processing to free some unused
>> page tables created in direct kernel mapping.
>>
>
> It might be good to split out the freeing of the page
> tables into a separate patch for review since it looks to be
> separate of DEBUG_PAGEALLOC.
>
Yes. It is not relative to DEBUG_PAGEALLOC.
I just think it is small change, so do not break down it.
But it is not right.

I will separate it.
>> The patch was tested based on the following code @:
>> https://git.linaro.org/people/zhichang.yuan/pgalloc.git/shortlog/refs/heads/test_pgalloc_v1
>>
>> Signed-off-by: Zhichang Yuan <[email-masked]>
>> ---
>>   arch/arm64/Kconfig                     |    3 +
>>   arch/arm64/include/asm/pgtable-hwdef.h |    6 +
>>   arch/arm64/include/asm/pgtable.h       |   21 +++
>>   arch/arm64/mm/mmu.c                    |  263 +++++++++++++++++++++++++++++++-
>>   4 files changed, 288 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index fd4e81a..da072d4 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -128,6 +128,9 @@ config KERNEL_MODE_NEON
>>   config FIX_EARLYCON_MEM
>>       def_bool y
>>
>> +config ARCH_SUPPORTS_DEBUG_PAGEALLOC
>> +    def_bool y
>> +
>>   source "init/Kconfig"
>>
>>   source "kernel/Kconfig.freezer"
>> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
>> index 88174e0..0a62e9a 100644
>> --- a/arch/arm64/include/asm/pgtable-hwdef.h
>> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
>> @@ -65,6 +65,12 @@
>>   #define PUD_TYPE_SECT        (_AT(pgdval_t, 1) << 0)
>>
>>   /*
>> + * Section
>> + */
>> +#define PUD_SECT_VALID        (_AT(pmdval_t, 1) << 0)
>> +#define PUD_SECT_PROT_NONE    (_AT(pmdval_t, 1) << 58)
>> +
>> +/*
>>    * Level 2 descriptor (PMD).
>>    */
>>   #define PMD_TYPE_MASK        (_AT(pmdval_t, 3) << 0)
>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
>> index ffe1ba0..4246f3b 100644
>> --- a/arch/arm64/include/asm/pgtable.h
>> +++ b/arch/arm64/include/asm/pgtable.h
>> @@ -313,9 +313,12 @@ 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)
>> @@ -422,6 +425,14 @@ static inline pud_t *pud_offset(pgd_t *pgd, unsigned long addr)
>>   /* to find an entry in a kernel page-table-directory */
>>   #define pgd_offset_k(addr)    pgd_offset(&init_mm, addr)
>>
>> +
>> +#define PHYSICAL_PAGE_MASK    (((signed long)PAGE_MASK) & PHYS_MASK)
>> +/* PTE_PFN_MASK extracts the PFN from a (pte|pmd|pud|pgd)val_t */
>> +#define PTE_PFN_MASK        ((pteval_t)PHYSICAL_PAGE_MASK)
>> +
>> +/* PTE_FLAGS_MASK extracts the flags from a (pte|pmd|pud|pgd)val_t */
>> +#define PTE_FLAGS_MASK        (~PTE_PFN_MASK)
>> +
>>   static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>>   {
>>       const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
>> @@ -477,6 +488,16 @@ extern pgd_t idmap_pg_dir[PTRS_PER_PGD];
>>
>>   #define PTE_FILE_MAX_BITS    55
>>
>> +extern pte_t *lookup_kaddress(unsigned long address, unsigned int *level);
>> +
>> +enum pg_level {
>> +    PG_LEVEL_NONE,
>> +    PG_LEVEL_PAGE,
>> +    PG_LEVEL_PMD,
>> +    PG_LEVEL_PUD,
>> +    PG_LEVEL_NUM
>> +};
>> +
>>   extern int kern_addr_valid(unsigned long addr);
>>
>>   #include <asm-generic/pgtable.h>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index c555672..6bc5f70 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -132,10 +132,21 @@ EXPORT_SYMBOL(phys_mem_access_prot);
>>   static void __init *early_alloc(unsigned long sz)
>>   {
>>       void *ptr = __va(memblock_alloc(sz, sz));
>> +
>>       memset(ptr, 0, sz);
>>       return ptr;
>>   }
>>
>> +/*Free the page used as pmd table entry in direct mapping*/
>> +static inline void __init pmd_table_free(pmd_t *pmd, unsigned long addr)
>> +{
>> +    if (pmd_table(*pmd)) {
>> +        phys_addr_t table = __pa(pte_offset_kernel(pmd, 0));
>> +
>
> pte_offset_kernel -> pmd_page_vaddr which calls __va already. Is
> there another way to get the physical address without having to go
> pa -> va -> pa again?
>
Yes. It seems to be verbose when offset is 0. I want to use existed macro.
I think i had other two options.
First, directly get the physical address just like that:

pmd_val(*pmd) & PHYS_MASK & (s32)PAGE_MASK

or

pte_pfn(pmd_pte(*pmd)) << PAGE_SHIFT

Maybe the front one is better.

>> +        memblock_free(table, PAGE_SIZE);
>> +    }
>> +}
>> +
>>   static void __init alloc_init_pte(pmd_t *pmd, unsigned long addr,
>>                     unsigned long end, unsigned long pfn,
>>                     pgprot_t prot)
>> @@ -185,14 +196,16 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr,
>>           next = pmd_addr_end(addr, end);
>>           /* try section mapping first */
>>           if (((addr | next | phys) & ~SECTION_MASK) == 0) {
>> -            pmd_t old_pmd =*pmd;
>> +            pmd_t old_pmd = *pmd;
>> +
>>               set_pmd(pmd, __pmd(phys | prot_sect));
>>               /*
>>                * Check for previous table entries created during
>>                * boot (__create_page_tables) and flush them.
>>                */
>>               if (!pmd_none(old_pmd))
>> -                flush_tlb_all();
>> +                flush_tlb_kernel_range(addr, next);
> Was the switch from flush_tlb_all -> flush_tlb_kernel_range found from
> code inspection or as part of something else? Do you have any performance
> data about from this switch?
>
As for this issue, i have no performance data. But you can check the implementation of flush_tlb_kernel_range.
when the pages size to be flushed is over MAX_TLB_RANGE, it will call __flush_tlb_kernel_range; otherwise, same as
flush_tlb_all. I think someone had evaluated the performance difference.

>> +            pmd_table_free(&old_pmd, addr);
>>           } else {
>>               alloc_init_pte(pmd, addr, next, __phys_to_pfn(phys),
>>                          prot_pte);
>> @@ -224,6 +237,7 @@ static void __init alloc_init_pud(pgd_t *pgd, unsigned long addr,
>>           if (!map_io && (PAGE_SHIFT == 12) &&
>>               ((addr | next | phys) & ~PUD_MASK) == 0) {
>>               pud_t old_pud = *pud;
>> +
>>               set_pud(pud, __pud(phys | PROT_SECT_NORMAL_EXEC));
>>
>>               /*
>> @@ -234,9 +248,15 @@ 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();
>> +                flush_tlb_kernel_range(addr, next);
>> +                if (pud_table(old_pud)) {
>> +                    phys_addr_t table =
>> +                        __pa(pmd_offset(&old_pud, 0));
>> +                    pmd_t *pmd = pmd_offset(pud, addr);
>> +
>> +                    pmd_table_free(pmd, addr);
>> +                    memblock_free(table, PAGE_SIZE);
>> +                }
>>               }
>>           } else {
>>               alloc_init_pmd(pud, addr, next, phys, map_io);
>> @@ -287,6 +307,219 @@ void __init create_id_mapping(phys_addr_t addr, phys_addr_t size, int map_io)
>>                addr, addr, size, map_io);
>>   }
>>
>> +static inline pte_t *lookup_kaddress_in_pgd(pgd_t *pgd,
>> +            unsigned long address,
>> +            unsigned int *level)
>> +{
>> +    pud_t *pud;
>> +    pmd_t *pmd;
>> +
>> +    *level = PG_LEVEL_NONE;
>> +
>> +    if (pgd_none(*pgd))
>> +        return NULL;
>> +
>> +    pud = pud_offset(pgd, address);
>> +    if (pud_none(*pud))
>> +        return NULL;
>> +
>> +    *level = PG_LEVEL_PUD;
>> +    if (pud_sect(*pud) || !(pud_val(*pud) & PUD_SECT_VALID))
>> +        return (pte_t *)pud;
>> +
>> +    pmd = pmd_offset(pud, address);
>> +    if (pmd_none(*pmd))
>> +        return NULL;
>> +
>> +    /*
>> +    * !(pmd_val(*pmd) & PMD_SECT_VALID) means PMD_TYPE_MASK &(*pmd)
>> +    * is 0, but *pmd is non-zero.
>> +    * For Huge page split.
>> +    */
>> +    *level = PG_LEVEL_PMD;
>> +    if (pmd_sect(*pmd) || !(pmd_val(*pmd) & PMD_SECT_VALID))
>> +        return (pte_t *)pmd;
>> +
>> +    *level = PG_LEVEL_PAGE;
>> +
>> +    return pte_offset_kernel(pmd, address);
>> +}
>> +
>> +
>> +pte_t *lookup_kaddress(unsigned long address, unsigned int *level)
>> +{
>> +    return lookup_kaddress_in_pgd(pgd_offset_k(address), address, level);
>> +}
>> +EXPORT_SYMBOL_GPL(lookup_kaddress);
>
> Do you need the EXPORT_SYMBOL right now?
Because my original test code is module, and call this function.

>
>> +
>> +
>> +#ifdef CONFIG_DEBUG_PAGEALLOC
>> +
>> +static void __split_pmd_page_mapping(pmd_t *pmd,
>> +            unsigned long addr,
>> +            void *p_base)
>> +{
>> +    pte_t *pte_base;
>> +    int i;
>> +
>> +    pgprot_t prot_val;
>> +
>> +    unsigned long pfn;
>> +
>> +    pte_base = (pte_t *)p_base;
>> +
>> +    /*get the original pgprot value.*/
>> +    prot_val = pmd_val(*pmd) & PTE_FLAGS_MASK;
>> +    prot_val &= ~PTE_TYPE_MASK;
>> +    prot_val |= PTE_TYPE_PAGE;
>> +
>> +    pfn = pmd_pfn(*pmd);
>> +    for (i = 0; i < PTRS_PER_PTE; i++, pfn += 1)
>> +        set_pte(pte_base + i, pfn_pte(pfn, prot_val));
>> +
>> +    __pmd_populate(pmd, __pa(pte_base), PMD_TYPE_TABLE);
>> +    flush_tlb_kernel_range((addr & PMD_MASK),
>> +            ((addr + PMD_SIZE) & PMD_MASK));
>> +}
>> +
>> +
>> +static void __split_pud_page_mapping(pud_t *pud,
>> +            unsigned long addr,
>> +            void *p_base)
>> +{
>> +    int i;
>> +
>> +    pgprot_t old_prot;
>> +
>> +    unsigned long pfn, pfn_inc;
>> +
>> +    pmd_t *pmd_base = (pmd_t *)p_base;
>> +
>> +    /*get the original pgprot value.*/
>> +    old_prot = pud_val(*pud) & PTE_FLAGS_MASK;
>> +
>> +    pfn = pud_pfn(*pud);
>> +    pfn_inc = PMD_SIZE >> PAGE_SHIFT;
>> +    for (i = 0; i < PTRS_PER_PMD; i++, pfn += pfn_inc)
>> +        set_pmd(pmd_base + i, pfn_pmd(pfn, old_prot));
>> +
>> +    pud_populate(&init_mm, pud, pmd_base);
>> +    flush_tlb_all();
>
> Everywhere else you've switched to using flush_tlb_kernel_range,
> why the switch here to flush_tlb_all?
>
Since here process PUD, a larger size.
>> +}
>> +
>> +void kernel_map_pages(struct page *page, int numpages, int enable)
>> +{
>> +    unsigned long start_addr, end_addr, addr;
>> +    unsigned int level;
>> +
>> +    pte_t *kpte;
>> +    pteval_t old_pval, new_pval;
>> +
>> +    int i, counter = 0;
>> +
>> +    /*no highmem in ARMv8. */
>> +    addr = start_addr = (unsigned long)page_address(page);
>> +    end_addr = start_addr + (numpages << PAGE_SHIFT);
>> +
>> +    for (i = 0; i < numpages; addr += PAGE_SIZE, i++) {
>> +        kpte = lookup_kaddress(addr, &level);
>> +        /*
>> +        * skip the memory holes. it is impossible if the input
>> +        * parameter is valid.
>> +        */
>> +        if (unlikely(!kpte || pte_none(*kpte))) {
>> +            pr_err("Have no kernel linear mapping for 0x%0lx\n", addr);
>> +            break;
>> +        }
>> +
>> +        if (level != PG_LEVEL_PAGE) {
>> +            pr_err("Page entry for 0x%0lx is not PAGE LEVEL(%d)\n",
>> +                addr, level);
>> +            break;
>> +        }
>> +
>> +        old_pval = pte_val(*kpte);
>> +        new_pval = (enable) ? (old_pval | PTE_VALID) :
>> +            (old_pval & (~PTE_VALID));
>> +        if (unlikely(new_pval == old_pval)) {
>> +            pr_warn("Page %s: same pte value at 0x%llx",
>> +                (enable) ? "alloc" : "free", old_pval);
>> +            continue;
>> +        }
>> +
>> +        set_pte(kpte, __pte(new_pval));
>> +        counter++;
>> +    }
>> +
>> +    if (counter)
>> +        flush_tlb_kernel_range(start_addr, end_addr);
>> +}
>
> We already have some of this infrastructure to set page attributes
> in arch/arm64/mm/pageattr.c . We should be leveraging that for
> kernel_map_pages.
>
There is no pageattr.c for ARMv8. In X86, it exists.
Do you mean pmd_modify?

>> +
>> +
>> +static int __init early_split_large_page_mapping(unsigned long virt,
>> +            phys_addr_t phys,
>> +            phys_addr_t size)
>> +{
>> +    pte_t *pte;
>> +    void *pte_base;
>> +
>> +    unsigned long addr, end, next;
>> +    unsigned int pg_level;
>> +    unsigned long size_level;
>> +    unsigned long mask_level;
>> +
>> +    /*make the addr aligned to PAGE*/
>> +    addr = virt & PAGE_MASK;
>> +    end = addr + PAGE_ALIGN(size + (virt & ~PAGE_MASK));
>> +
>> +    for (; addr != end; phys += (next - addr), addr = next) {
>> +repeat:
>> +        pte = lookup_kaddress(addr, &pg_level);
>> +        /*
>> +        * support the input memory range is a wider range. If we
>> +        * can not find valid page entry for some addresses, we do
>> +        * not know the page section size. But we only care the
>> +        * large page, just move forward in minimal large page size
>> +        * (PMD size)
>> +        */
>> +        if (!pte || pte_none(*pte)) {
>> +            next = pmd_addr_end(addr, end);
>> +            continue;
>> +        }
>> +
>> +        size_level = (_AC(1, UL) <<
>> +            ((PAGE_SHIFT - 3) * pg_level + 3));
>> +        mask_level = ~(size_level - 1);
>> +
>> +        next = (addr + size_level) & mask_level;
>> +        if (next > end)
>> +            next = end;
>> +
>> +        /*Does it need to split it?*/
>> +        if (pg_level == PG_LEVEL_PAGE)
>> +            continue;
>> +
>> +        /*start the splitting...*/
>> +        if (pte_pfn(*pte) != PFN_DOWN(phys & mask_level)) {
>> +            pr_err("Physical addr 0x%0llx mis-match with virt 0x%0lx\n",
>> +                    pte_pfn(*pte), addr & mask_level);
>> +            return -1;
>
> Return a real error code here and not just -1
>
Yes. Maybe EFAULT is more better.
>> +        }
>> +
>> +        pte_base = early_alloc(PAGE_SIZE);
>> +
>> +        if (pg_level == PG_LEVEL_PUD) {
>> +            __split_pud_page_mapping((pud_t *)pte, addr, pte_base);
>> +            goto repeat;
>
> This looks like a less friendly use of goto. Any change we could turn this
> into a real loop?
>
I just want to make __split_pud_page_mapping more concise and just for the split from pud to pmd.

Best,
-Zhichang
>> +        }
>> +        __split_pmd_page_mapping((pmd_t *)pte, addr, pte_base);
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +
>> +#endif
>>   static void __init map_mem(void)
>>   {
>>       struct memblock_region *reg;
>> @@ -331,6 +564,26 @@ static void __init map_mem(void)
>>           create_mapping(start, __phys_to_virt(start), end - start);
>>       }
>>
>> +#ifdef CONFIG_DEBUG_PAGEALLOC
>> +    /*
>> +    * the biggest direct mapping is ready, then start the PTE building.
>> +    * Now,there are sufficient mapped pages to store the PTE tables.
>> +    * And more important, doing large page splitting here can dispose
>> +    * the page tables in contiguous memory area.
>> +    */
>> +    for_each_memblock(memory, reg) {
>> +        phys_addr_t start = reg->base;
>> +        phys_addr_t end = start + reg->size;
>> +
>> +        if (start >= end || PFN_UP(start) >= PFN_DOWN(end))
>> +            break;
>> +
>> +        if (early_split_large_page_mapping(__phys_to_virt(start),
>> +                start, end - start))
>> +            panic("map_mem:Fail to split large page[0x%0llx,0x%0llx)\n",
>> +                start, end);
>> +    }
>> +#endif
>>       /* Limit no longer required. */
>>       memblock_set_current_limit(MEMBLOCK_ALLOC_ANYWHERE);
>>   }
>>
>
> Thanks,
> Laura
>