Re: [PATCH v4 3/3] x86/kdump/64: Change the upper limit of crashkernel reservation

Baoquan He
2019-05-23T03:15:58Z

On 05/22/19 at 11:11am, Dave Young wrote:
> > /*
> > - * Keep the crash kernel below this limit. On 32 bits earlier kernels
> > - * would limit the kernel to the low 512 MiB due to mapping restrictions.
> > + * Keep the crash kernel below this limit.
> > + *
> > + * On 32 bits earlier kernels would limit the kernel to the low
> > + * 512 MiB due to mapping restrictions.
> > + *
> > + * On 64bit, old kexec-tools need to be under 896MiB. The later
> > + * supports to put kernel above 4G, up to system RAM top. Here
>
> Above two lines are not reflected in code because we have removed
> the 896M limitation, it would be better to drop the two lines to
> avoid confusion.

Missed these comments at bottom of mail.

Yes, will remove these two lines.

>
> > + * kdump kernel need be restricted to be under 64TB, which is
> > + * the upper limit of system RAM in 4-level paing mode. Since
> > + * the kdump jumping could be from 5-level to 4-level, the jumping
> > + * will fail if kernel is put above 64TB, and there's no way to
> > + * detect the paging mode of the kernel which will be loaded for
> > + * dumping during the 1st kernel bootup.
> > */
> > #ifdef CONFIG_X86_32
> > # define CRASH_ADDR_LOW_MAX SZ_512M
> > # define CRASH_ADDR_HIGH_MAX SZ_512M
> > #else
> > # define CRASH_ADDR_LOW_MAX SZ_4G
> > -# define CRASH_ADDR_HIGH_MAX MAXMEM
> > +# define CRASH_ADDR_HIGH_MAX (64UL << 40)
>
> Maybe add a new macro in sizes.h like SZ_64T

I am fine, will add and use it here. Thanks.