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

[Baoquan He]

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.

> +			(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
>