Re: [PATCH 02/24] x86: Make sure free_init_pages() free pages inboundary

[Yinghai Lu]

On 03/26/2010 04:06 PM, Johannes Weiner wrote:
> On Fri, Mar 26, 2010 at 03:21:32PM -0700, Yinghai Lu wrote:
>> diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
>> index adedeef..fe3d953 100644
>> --- a/arch/x86/kernel/head32.c
>> +++ b/arch/x86/kernel/head32.c
>> @@ -47,6 +47,7 @@ void __init i386_start_kernel(void)
>>  		u64 ramdisk_image = boot_params.hdr.ramdisk_image;
>>  		u64 ramdisk_size  = boot_params.hdr.ramdisk_size;
>>  		u64 ramdisk_end   = ramdisk_image + ramdisk_size;
>> +		ramdisk_end = PFN_UP(ramdisk_end) << PAGE_SHIFT;
> 
> Why not PAGE_ALIGN()?

looks like PFN_UP is more clear.

>> +	size_aligned = ramdisk_end - ramdisk_image;
>> +
>>  	/* We need to move the initrd down into lowmem */
>> -	ramdisk_here = find_e820_area(0, end_of_lowmem, ramdisk_size,
>> +	ramdisk_here = find_e820_area(0, end_of_lowmem, size_aligned,
>>  					 PAGE_SIZE);
>>  
>>  	if (ramdisk_here == -1ULL)
>>  		panic("Cannot find place for new RAMDISK of size %lld\n",
>> -			 ramdisk_size);
>> +			 size_aligned);
>>  
>>  	/* Note: this includes all the lowmem currently occupied by
>>  	   the initrd, we rely on that fact to keep the data intact. */
>> -	reserve_early(ramdisk_here, ramdisk_here + ramdisk_size,
>> +	reserve_early(ramdisk_here, ramdisk_here + size_aligned,
>>  			 "NEW RAMDISK");
>>  	initrd_start = ramdisk_here + PAGE_OFFSET;
>>  	initrd_end   = initrd_start + ramdisk_size;
>>  	printk(KERN_INFO "Allocated new RAMDISK: %08llx - %08llx\n",
>> -			 ramdisk_here, ramdisk_here + ramdisk_size);
>> +			 ramdisk_here, ramdisk_here + size_aligned);
>>  
>>  	q = (char *)initrd_start;
>>  
>>  	/* Copy any lowmem portion of the initrd */
>> -	if (ramdisk_image < end_of_lowmem) {
>> -		clen = end_of_lowmem - ramdisk_image;
>> -		p = (char *)__va(ramdisk_image);
>> +	image = ramdisk_image;
>> +	if (image < end_of_lowmem) {
>> +		clen = end_of_lowmem - image;
>> +		p = (char *)__va(image);
>>  		memcpy(q, p, clen);
>>  		q += clen;
>> -		ramdisk_image += clen;
>> -		ramdisk_size  -= clen;
>> +		image += clen;
>> +		size_aligned  -= clen;
>>  	}
>>  
>>  	/* Copy the highmem portion of the initrd */
>> -	while (ramdisk_size) {
>> -		slop = ramdisk_image & ~PAGE_MASK;
>> -		clen = ramdisk_size;
>> +	while (size_aligned) {
>> +		slop = image & ~PAGE_MASK;
>> +		clen = size_aligned;
>>  		if (clen > MAX_MAP_CHUNK-slop)
>>  			clen = MAX_MAP_CHUNK-slop;
>> -		mapaddr = ramdisk_image & PAGE_MASK;
>> +		mapaddr = image & PAGE_MASK;
>>  		p = early_memremap(mapaddr, clen+slop);
>>  		memcpy(q, p+slop, clen);
>>  		early_iounmap(p, clen+slop);
>>  		q += clen;
>> -		ramdisk_image += clen;
>> -		ramdisk_size  -= clen;
>> +		image += clen;
>> +		size_aligned  -= clen;
> 
> Those appear to be a lot of spurious changes.  We don't need to
> copy the alignment padding as well, so it only matters that the
> arguments to find_e820_area() and reserve_early() are aligned, no?

we need to reserve that whole page, otherwise other user may use the same page.

then we can not use PFN_UP() later to free the whole page.

>> --- a/arch/x86/mm/init.c
>> +++ b/arch/x86/mm/init.c
>> @@ -332,6 +332,16 @@ int devmem_is_allowed(unsigned long pagenr)
>>  void free_init_pages(char *what, unsigned long begin, unsigned long end)
>>  {
>>  	unsigned long addr = begin;
>> +	unsigned long addr_aligned, end_aligned;
>> +
>> +	/* Make sure boundaries are page aligned */
>> +	addr_aligned = PFN_UP(addr) << PAGE_SHIFT;
>> +	end_aligned = PFN_DOWN(end) << PAGE_SHIFT;
>> +
>> +	if (WARN(addr_aligned != addr || end_aligned != end, "free_init_pages: range [%#lx, %#lx] is not aligned\n", addr, end)) {
>> +		addr = addr_aligned;
>> +		end = end_aligned;
>> +	}
> 
> Maybe realign only for when it is not aligned?  So to keep the fixup
> out of line.
> 
> I suppose WARN_ON() is enough as it will print a stack trace which
> should be enough clue of what went wrong.

we need to PFN_DOWN the end, and don't free the partial page.
otherwise could crash the system.

So just print out the trace, and system still can be used. reporter to get dmesg if
he don't have serial console.

> 
>>  	if (addr >= end)
>>  		return;
>> @@ -376,6 +386,18 @@ void free_initmem(void)
>>  #ifdef CONFIG_BLK_DEV_INITRD
>>  void free_initrd_mem(unsigned long start, unsigned long end)
>>  {
>> -	free_init_pages("initrd memory", start, end);
>> +	unsigned long end_aligned;
>> +
>> +	/*
>> +	 * end could be not aligned, and We can not align that,
>> +	 * decompresser could be confused by aligned initrd_end
>> +	 * We already reserve the end partial page before in
>> +	 *   - i386_start_kernel()
>> +	 *   - x86_64_start_kernel()
>> +	 *   - relocate_initrd()
>> +	 * So here we can do PFN_UP() safely to get partial page to be freed
>> +	 */
>> +	end_aligned = PFN_UP(end) << PAGE_SHIFT;
> 
> PAGE_ALIGN()

no PAGE_ALIGN is bad name, it is not clear UP or DOWN.

Thanks

Yinghai
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