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

From: [email-masked] (zhichang.yuan)
Date: Wed, 17 Dec 2014 09:49:23 +0800

Hi, Laura,

On 2014?10?30? 06:23, Laura Abbott wrote:
> On 10/27/2014 11:11 PM, zhichang.yuan wrote:
>> Hi, Laura,
>>
>> Thanks for your comments!
>>
>>
>>
> ...
>>>> +}
>>>> +
>>>> +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?
>>
> 
> It was added to the kernel fairly recently
> 
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=11d91a770f1fff44dafdf88d6089a3451f99c9b6
> 

I browsed the pageattr.c, the functions which modify the page table entry attributes are good. But the base
function, change_memory_common, is limited for module memory space. It will make the relative functions are
not common. Can we do some changes on it?

thanks,
-Zhichang

> Thanks,
> Laura