On Fri, Jan 25, 2019 at 6:39 PM Borislav Petkov <bp@xxxxxxxxx> wrote: > > > > Subject: Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X > > s/bugfix, // > OK. > On Mon, Jan 21, 2019 at 01:16:08PM +0800, Pingfan Liu wrote: > > People reported crashkernel=384M reservation failed on a high end server > > with KASLR enabled. In that case there is enough free memory under 896M > > but crashkernel reservation still fails intermittently. > > > > The situation is crashkernel reservation code only finds free region under > > 896 MB with 128M aligned in case no ',high' being used. And KASLR could > > break the first 896M into several parts randomly thus the failure happens. > > This reads very strange. > What about " It turns out that crashkernel reservation code only tries to find a region under 896 MB, aligned on 128M. But KASLR randomly breaks big region inside [0,896M] into smaller pieces, not big enough as demanded in the "crashkernel=X" parameter." > > User has no way to predict and make sure crashkernel=xM working unless > > he/she use 'crashkernel=xM,high'. Since 'crashkernel=xM' is the most > > common use case this issue is a serious bug. > > > > And we can't answer questions raised from customer: > > 1) why it doesn't succeed to reserve 896 MB; > > 2) what's wrong with memory region under 4G; > > 3) why I have to add ',high', I only require 384 MB, not 3840 MB. > > Errr, this looks like communication issue. Sounds to me like the text > around crashkernel= in > What about dropping this section in commit log and another patch to fix the document? > Documentation/admin-guide/kernel-parameters.txt > > needs improving? > > > This patch tries to get memory region from 896 MB firstly, then [896MB,4G], > > Avoid having "This patch" or "This commit" in the commit message. It is > tautologically useless. > OK > Also, do > > $ git grep 'This patch' Documentation/process > > for more details. > > > finally above 4G. > > > > Dave Young sent the original post, and I just re-post it with commit log > > If he sent it, he should be the author I guess. > > > improvement as his requirement. > > http://lists.infradead.org/pipermail/kexec/2017-October/019571.html > > There was an old discussion below (previously posted by Chao Wang): > > https://lkml.org/lkml/2013/10/15/601 > > All that changelog info doesn't belong in the commit message ... > > > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx> > > Cc: Dave Young <dyoung@xxxxxxxxxx> > > Cc: Baoquan He <bhe@xxxxxxxxxx> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> > > Cc: yinghai@xxxxxxxxxx, > > Cc: vgoyal@xxxxxxxxxx > > Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > > Cc: Borislav Petkov <bp@xxxxxxxxx> > > Cc: x86@xxxxxxxxxx > > Cc: linux-kernel@xxxxxxxxxxxxxxx > > --- > > .... but here. > > > v6 -> v7: commit log improvement > > arch/x86/kernel/setup.c | 16 ++++++++++++++++ > > 1 file changed, 16 insertions(+) > > > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > > index 3d872a5..fa62c81 100644 > > --- a/arch/x86/kernel/setup.c > > +++ b/arch/x86/kernel/setup.c > > @@ -551,6 +551,22 @@ static void __init reserve_crashkernel(void) > > high ? CRASH_ADDR_HIGH_MAX > > : CRASH_ADDR_LOW_MAX, > > crash_size, CRASH_ALIGN); > > +#ifdef CONFIG_X86_64 > > + /* > > + * crashkernel=X reserve below 896M fails? Try below 4G > > + */ > > + if (!high && !crash_base) > > + crash_base = memblock_find_in_range(CRASH_ALIGN, > > + (1ULL << 32), > > + crash_size, CRASH_ALIGN); > > + /* > > + * crashkernel=X reserve below 4G fails? Try MAXMEM > > + */ > > + if (!high && !crash_base) > > + crash_base = memblock_find_in_range(CRASH_ALIGN, > > + CRASH_ADDR_HIGH_MAX, > > + crash_size, CRASH_ALIGN); > > +#endif > > Ok, so this is silly: we know at which physical address KASLR allocated > the kernel so why aren't we querying that and seeing if there's enough > room before it or after it to call memblock_find_in_range() on the > bigger range? > Sorry, can not catch up with you. Do you suggestion memblock_find_in_range(0, kernel_start) and memblock_find_in_range(kernel_end, mem_end)? But the memory is truncated into fraction by many component which call memblock_reserve(), besides kernel. For the left question, Dave has follow the discussion in another email, will follow there. Thanks and regards, Pingfan > Also, why is "high" dealt with separately and why isn't the code > enforcing "high" if the normal reservation fails? > > The presence of high is requiring from our users to pay attention what > to use when the kernel can do all that automatically. Looks like a UI > fail to me. > > And look at all the flavors of crashkernel= : > > crashkernel=size[KMG][@offset[KMG]] > crashkernel=range1:size1[,range2:size2,...][@offset] > crashkernel=size[KMG],high > crashkernel=size[KMG],low > > We couldn't do one so we made 4?!?! > > What for? > > Nowhere in that help text does it explain why a user would care about > high or low or range or offset or the planets alignment... > > So what's up? > > -- > Regards/Gruss, > Boris. > > Good mailing practices for 400: avoid top-posting and trim the reply. _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
