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

From: Tang Chen <[email-masked]>
Date: Fri, 07 Dec 2012 14:43:46 +0800

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.

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