[PATCH v6 0/8] kdump, vmcore: support mmap() on /proc/vmcore

HATAYAMA Daisuke d.hatayama at jp.fujitsu.com
Thu May 16 21:45:36 EDT 2013

(2013/05/17 9:06), H. Peter Anvin wrote:
> On 05/15/2013 02:05 AM, HATAYAMA Daisuke wrote:
>> Currently, read to /proc/vmcore is done by read_oldmem() that uses
>> ioremap/iounmap per a single page. For example, if memory is 1GB,
>> ioremap/iounmap is called (1GB / 4KB)-times, that is, 262144
>> times. This causes big performance degradation.
> read_oldmem() is fundamentally broken and unsafe.  It needs to be
> unified with the plain /dev/mem code and any missing functionality fixed
> instead of "let's just do a whole new driver".
> 	-hpa

Do you mean range_is_allowed should be extended so that it checks 
according to memory map passed from the 1st kernel?

BTW, read request to read_oldmem via read_vmcore and mmap on some part 
of the 1st kernel, seems safe since it's always restrected to within the 
memory map.

Or is there other missing point?


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