Subject: Re: [Patch v4 09/12] memory-hotplug: remove page table of x86_64 architecture

From: Jianguo Wu <[email-masked]>
Date: Fri, 7 Dec 2012 15:06:16 +0800

On 2012/12/7 14:43, Tang Chen wrote:

> On 11/27/2012 06:00 PM, Wen Congyang wrote:
>> For hot removing memory, we sholud remove page table about the memory.
>> So the patch searches a page table about the removed memory, and clear
>> page table.
> 
> (snip)
> 
>> +void __meminit
>> +kernel_physical_mapping_remove(unsigned long start, unsigned long end)
>> +{
>> +    unsigned long next;
>> +    bool pgd_changed = false;
>> +
>> +    start = (unsigned long)__va(start);
>> +    end = (unsigned long)__va(end);
> 
> Hi Wu,
> 
> Here, you expect start and end are physical addresses. But in
> phys_xxx_remove() function, I think using virtual addresses is just
> fine. Functions like pmd_addr_end() and pud_index() only calculate
> an offset.
>

Hi Tang,

Virtual addresses will work fine, I used physical addresses in order to
keep consistent with phys_pud[pmd/pte]_init(), So I think we should keep this.

Thanks,
Jianguo Wu

> So, would you please tell me if we have to use physical addresses here ?
> 
> Thanks. :)
> 
>> +
>> +    for (; start<  end; start = next) {
>> +        pgd_t *pgd = pgd_offset_k(start);
>> +        pud_t *pud;
>> +
>> +        next = pgd_addr_end(start, end);
>> +
>> +        if (!pgd_present(*pgd))
>> +            continue;
>> +
>> +        pud = map_low_page((pud_t *)pgd_page_vaddr(*pgd));
>> +        phys_pud_remove(pud, __pa(start), __pa(next));
>> +        if (free_pud_table(pud, pgd))
>> +            pgd_changed = true;
>> +        unmap_low_page(pud);
>> +    }
>> +
>> +    if (pgd_changed)
>> +        sync_global_pgds(start, end - 1);
>> +
>> +    flush_tlb_all();
>> +}
>> +
>>   #ifdef CONFIG_MEMORY_HOTREMOVE
>>   int __ref arch_remove_memory(u64 start, u64 size)
>>   {
>> @@ -692,6 +921,8 @@ int __ref arch_remove_memory(u64 start, u64 size)
>>       ret = __remove_pages(zone, start_pfn, nr_pages);
>>       WARN_ON_ONCE(ret);
>>
>> +    kernel_physical_mapping_remove(start, start + size);
>> +
>>       return ret;
>>   }
>>   #endif
> 
> 
> 
> .
>