On Fri, Feb 07, 2014 at 08:04:13AM -0800, H. Peter Anvin wrote: > On 02/07/2014 06:49 AM, Vivek Goyal wrote: > > > > Hi Kees, > > > > Dave Young is testing kdump with kaslr enabled. He is facing some issues. > > > > One issue he mentioned is that when second kernel boots, it might be > > placed in an area which is outside the reserved area for second kernel. > > > > We reserve a certain memory for second kernel. And modify memory map of > > second kernel using memmap=exactmap parameter. Looks like kernel placement > > is happening before memmap=exactmap takes effect. And that seems to be > > the reason that second kernel can be placed outside the reserved memory. > > > > IOW, memmap=exactmap and kaslr don't work together. Is it possible to > > first let memmap=exactmap take affect and then kaslr does its job. Or it > > is too late by the time memmap=exactmap is parsed. > > > > As a workaround, Dave is currently using "nokaslr" command line parameter > > for second kernel. He is still facing issues where makedumpfile segment > > faults. He is looking into it further. > > > > I thought I will atleast bring up with issue of memmap=exactmap and kaslr > > being incompatible. > > > > Yes, because memmap=exactmap gets parsed too late; kaslr assumes that > the e820 information passed to it is actually correct. > > Yet another cause of breakage caused by the decision on the part of > kdump to rely on command-line options. [CC kexec mailing list] Ok, I think this is high time we change kexec-tools to not use memmap=exactmap and start passing modified memory map in bootparams. I think only concern with that change was backward compatibility of kexec-tools with older kernels. IIUC, only thing which will be impacted by this change is users of saved_max_pfn which determine the highest accessible pfn in first kernel. Some calgary IOMMU code seems to be the only user of it now. So may be we can create a new command line option say --pass-memmap-cmdline to kexec-tools which forces old behavior and by default we pass memmap in bootparams. Or create --do-not-pass-memmap-cmdline and new users will use it. Default will be old behavior. Thansk Vivek
