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

[Baoquan He]

On 05/22/19 at 11:11am, Dave Young wrote:
> Hi Baoquan,
> 
> A few nitpicks, otherwise
> Acked-by: Dave Young <dyoung@xxxxxxxxxx>
> 
> On 05/09/19 at 09:36am, Baoquan He wrote:
> > Restrict kdump to only reserve crashkernel below 64TB.
> > 
> > The reaons is that the kdump may jump from 5-level to 4-level, and if
> > the kdump kernel is put above 64TB, then the jumping will fail. While the
> > 1st kernel reserves crashkernel region during bootup, we don't know yet
> > which kind of kernel will be loaded after system bootup, 5-level kernel
> > or 5-level kernel.
> 
> 5-level kernel or 4-level kernel ?

Right, it's typo. Should be '5-level kernel or 4-level kernel'. Thanks.

Will update.

> > 
> > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > ---
> >  arch/x86/kernel/setup.c | 17 ++++++++++++++---
> >  1 file changed, 14 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> > index 905dae880563..efb0934a46f6 100644
> > --- a/arch/x86/kernel/setup.c
> > +++ b/arch/x86/kernel/setup.c
> > @@ -452,15 +452,26 @@ static void __init memblock_x86_reserve_range_setup_data(void)
> >  #define CRASH_ALIGN		SZ_16M
> >  
> >  /*
> > - * 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. 
> 
> > + * 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
> 
> >  #endif
> >  
> >  static int __init reserve_crashkernel_low(void)
> > -- 
> > 2.17.2
> > 
> 
> Thanks
> Dave