On Monday 13 February 2017 01:58 PM, Atsushi Kumagai wrote: >> On Monday 13 February 2017 11:56 AM, Atsushi Kumagai wrote: >>> Hello Pratyush, >>> >>>> `makedumpfile --mem-usage /proc/kcore` has been broken after kaslr specific >>>> modifications. I have proposed a kernel patch [0] which has been ACKed by >>>> Andrew Morton and is available in next-2017020 now. Hopefully, it should be >>>> part of upstream in v4.10 release. This kernel patch helps to fix this >>>> issue for both the case of kaslr enabled and disabled. >>>> >>>> To seek other's feedback, I am sending makedumpfile patches before kernel >>>> patch hits upstream. >>> >>> Thanks for taking care of this feature. >>> I understand that the problem is: >>> >>> - phys_base is necessary for VtoP, but: >>> - SYMBOL(phys_base) is unavailable since /proc/kcore doesn't export VMCOREINFO. >>> - get_phys_base() doesn't work well since current PT_LOAD doesn't have valid p_paddr. >> >> Yes, this is what the problem is. >> >>> >>> The new makedumpfile with this patches can show unexpected behavior since it >>> will refer to invalid p_paddr(always 0). Of course, also current makedumpfile cannot >>> work if phys_base isn't 0. >>> >>> If we don't have any way to get phys_base in 1st kernel environment, >>> I think we should disable this feature in older kernel (e.g. by checking kernel version). >> >> Hummm..I had thought that distros with old kernel will backport kernel >> patch and then can use this feature. If we disable it for older kernel, >> then they will not be able to do it. >> >> would it be fine if I cc kernel patch to stable mailing list? It seems >> that patch can be easily applied all older kernel. > > Even if there are some "supported" older kernels, there is no guarantee > that all of the kernels provide valid p_paddr. So makedumpfile have to > know whether the target kernel supports --mem-usage or not in older kernel. > > Is it possible to add a new stuff into PT_NOTE of /proc/kcore to signify the > kernel supports --mem-usage ? Otherwise, my only idea is --force option for > older kernel, expert user can use it if he is sure that the kernel has valid > p_paddr. > I think, we can go with --force. I will send next revision after kernel patch hits Linus's tree. Thanks for your review. ~Pratyush
