Re: [PATCHv4] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr

[Pingfan Liu]

On Fri, Jan 4, 2019 at 5:43 PM Baoquan He <bhe@xxxxxxxxxx> wrote:
>
> On 01/04/19 at 04:39pm, Pingfan Liu wrote:
> > Customer reported a bug on a high end server with many pcie devices, where
> > kernel bootup with crashkernel=384M, and kaslr is enabled. Even
> > though we still see much memory under 896 MB, the finding still failed
> > intermittently. Because currently we can only find region under 896 MB,
> > if w/0 ',high' specified. Then KASLR breaks 896 MB into several parts
> > randomly, and crashkernel reservation need be aligned to 128 MB, that's
> > why failure is found. It raises confusion to the end user that sometimes
> > crashkernel=X works while sometimes fails.
> > If want to make it succeed, customer can change kernel option to
> > "crashkernel=384M, high". Just this give "crashkernel=xx@yy" a very
> > limited space to behave even though its grammer looks more generic.
> > And we can't answer questions raised from customer that confidently:
> > 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.
> >
> > This patch simplifies the method suggested in the mail [1]. It just goes
> > bottom-up to find a candidate region for crashkernel. The bottom-up may be
> > better compatible with the old reservation style, i.e. still want to get
> > memory region from 896 MB firstly, then [896 MB, 4G], finally above 4G.
> >
> > There is one trivial thing about the compatibility with old kexec-tools:
> > if the reserved region is above 896M, then old tool will fail to load
> > bzImage. But without this patch, the old tool also fail since there is no
> > memory below 896M can be reserved for crashkernel.
> >
> > [1]: http://lists.infradead.org/pipermail/kexec/2017-October/019571.html
> > Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
> > Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
> > Cc: Len Brown <lenb@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> > Cc: Michal Hocko <mhocko@xxxxxxxx>
> > Cc: Jonathan Corbet <corbet@xxxxxxx>
> > Cc: Yaowei Bai <baiyaowei@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> > Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> > Cc: Daniel Vacek <neelx@xxxxxxxxxx>
> > Cc: Mathieu Malaterre <malat@xxxxxxxxxx>
> > Cc: Stefan Agner <stefan@xxxxxxxx>
> > Cc: Dave Young <dyoung@xxxxxxxxxx>
> > Cc: Baoquan He <bhe@xxxxxxxxxx>
> > Cc: yinghai@xxxxxxxxxx
> > Cc: vgoyal@xxxxxxxxxx
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > ---
> > v3 -> v4:
> >  instead of exporting the stage of parsing mem hotplug info, just using the bottom-up allocation func directly
> >  arch/x86/kernel/setup.c  | 8 ++++----
> >  include/linux/memblock.h | 4 ++++
> >  mm/memblock.c            | 2 +-
> >  3 files changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> > index d494b9b..082aadd 100644
> > --- a/arch/x86/kernel/setup.c
> > +++ b/arch/x86/kernel/setup.c
> > @@ -546,10 +546,10 @@ static void __init reserve_crashkernel(void)
> >                * as old kexec-tools loads bzImage below that, unless
> >                * "crashkernel=size[KMG],high" is specified.
> >                */
> > -             crash_base = memblock_find_in_range(CRASH_ALIGN,
> > -                                                 high ? CRASH_ADDR_HIGH_MAX
> > -                                                      : CRASH_ADDR_LOW_MAX,
> > -                                                 crash_size, CRASH_ALIGN);
> > +             crash_base = __memblock_find_range_bottom_up(CRASH_ALIGN,
>
> Better make a wrapper function for external invocation. E.g we need
> allocate kernel data in mirrorred memory region if it's available. This
> has been done in memblock_find_in_range(), and the boundary alignment.
>
OK, I will update v5.
Thanks for your kindly review.

Regards,
Pingfan
> > +                     (max_pfn * PAGE_SIZE), crash_size, CRASH_ALIGN,
> > +                     NUMA_NO_NODE, MEMBLOCK_NONE);
> > +
> >               if (!crash_base) {
> >                       pr_info("crashkernel reservation failed - No suitable area found.\n");
> >                       return;
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index aee299a..39720bf 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -116,6 +116,10 @@ phys_addr_t memblock_find_in_range_node(phys_addr_t size, phys_addr_t align,
> >                                       int nid, enum memblock_flags flags);
> >  phys_addr_t memblock_find_in_range(phys_addr_t start, phys_addr_t end,
> >                                  phys_addr_t size, phys_addr_t align);
> > +phys_addr_t __init_memblock
> > +__memblock_find_range_bottom_up(phys_addr_t start, phys_addr_t end,
> > +                             phys_addr_t size, phys_addr_t align, int nid,
> > +                             enum memblock_flags flags);
> >  void memblock_allow_resize(void);
> >  int memblock_add_node(phys_addr_t base, phys_addr_t size, int nid);
> >  int memblock_add(phys_addr_t base, phys_addr_t size);
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index 81ae63c..53b1707 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -172,7 +172,7 @@ bool __init_memblock memblock_overlaps_region(struct memblock_type *type,
> >   * Return:
> >   * Found address on success, 0 on failure.
> >   */
> > -static phys_addr_t __init_memblock
> > +phys_addr_t __init_memblock
> >  __memblock_find_range_bottom_up(phys_addr_t start, phys_addr_t end,
> >                               phys_addr_t size, phys_addr_t align, int nid,
> >                               enum memblock_flags flags)
> > --
> > 2.7.4
> >