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

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Date:   Thu, 23 May 2019 11:15:41 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...nel.org,
        bp@...en8.de, hpa@...or.com, kirill.shutemov@...ux.intel.com,
        x86@...nel.org
Subject: Re: [PATCH v4 3/3] x86/kdump/64: Change the upper limit of
 crashkernel reservation

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.