Re: [PATCHv7] x86/kdump: bugfix, make the behavior of crashkernel=X consistent with kaslr

[Baoquan He]

On 01/21/19 at 01:16pm, 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.
> 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.
> 
> This patch tries to get memory region from 896 MB firstly, then [896MB,4G],
> finally above 4G.
> 
> Dave Young sent the original post, and I just re-post it with commit log
> 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
> 
> 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

Looks good, ack.

Acked-by: Baoquan He <bhe@xxxxxxxxxx>

Thanks
Baoquan

> ---
> 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
>  		if (!crash_base) {
>  			pr_info("crashkernel reservation failed - No suitable area found.\n");
>  			return;
> -- 
> 2.7.4
>