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Date: Mon, 7 Jan 2019 16:02:48 +0800
From: Pingfan Liu <kernelfans@...il.com>
To: Baoquan He <bhe@...hat.com>
Cc: kexec@...ts.infradead.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
Len Brown <lenb@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Rapoport <rppt@...ux.vnet.ibm.com>,
Michal Hocko <mhocko@...e.com>,
Jonathan Corbet <corbet@....net>,
Yaowei Bai <baiyaowei@...s.chinamobile.com>,
Nicholas Piggin <npiggin@...il.com>,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Daniel Vacek <neelx@...hat.com>,
Mathieu Malaterre <malat@...ian.org>,
Stefan Agner <stefan@...er.ch>, Dave Young <dyoung@...hat.com>,
yinghai@...nel.org, vgoyal@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4] x86/kdump: bugfix, make the behavior of crashkernel=X
consistent with kaslr
On Fri, Jan 4, 2019 at 5:43 PM Baoquan He <bhe@...hat.com> 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@...il.com>
> > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > Cc: Len Brown <lenb@...nel.org>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> > Cc: Michal Hocko <mhocko@...e.com>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: Yaowei Bai <baiyaowei@...s.chinamobile.com>
> > Cc: Nicholas Piggin <npiggin@...il.com>
> > Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> > Cc: Daniel Vacek <neelx@...hat.com>
> > Cc: Mathieu Malaterre <malat@...ian.org>
> > Cc: Stefan Agner <stefan@...er.ch>
> > Cc: Dave Young <dyoung@...hat.com>
> > Cc: Baoquan He <bhe@...hat.com>
> > Cc: yinghai@...nel.org
> > Cc: vgoyal@...hat.com
> > Cc: linux-kernel@...r.kernel.org
> > ---
> > 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
> >
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