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From: Dave Young <dyoung@redhat.com>
Date: Thu, 21 Mar 2024 08:57:01 +0800
Message-ID: <CALu+AoR3QA58_WJVLc06ma5RC69jYLi2BHBsq1fvxK07amNSaw@mail.gmail.com>
Subject: Re: [PATCH] x86/kexec: do not update E820 kexec table for setup_data
To: "Huang, Kai" <kai.huang@intel.com>
Cc: x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, 
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, 
	"H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, 
	Baoquan He <bhe@redhat.com>, Eric Biederman <ebiederm@xmission.com>
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Hi,

On Thu, 21 Mar 2024 at 05:56, Huang, Kai <kai.huang@intel.com> wrote:
>
> Hi Dave,
>
> Some nitpicking in changelog:

Will fix the grammar issues.  Thanks for your review!

>
> On 5/03/2024 2:32 pm, Dave Young wrote:
> > crashkernel reservation failed on a Thinkpad t440s laptop recently,
>
> ',' -> '.' to make it as a standalone sentence.
>
> > Actually the memblock reservation succeeded, but later insert_resource()
> > failed.
> >
> > Test step:
> > kexec load ->
> >       kexec reboot ->
> >               check the crashkernel memory
> >               dmesg|grep "crashkernel reserved"; saw reserved suceeeded:
>
> "suceeeded" -> "succeeded".
>
> >               0x00000000d0000000 - 0x00000000da000000
> >               grep Crash /proc/iomem: got nothing
>
> And somehow I found it's not easy to read.  :-)
>
> >
> > The background story is like below:
>
> Better to have an blank line to make text more breathable.
>
> > Currently E820 code reserves setup_data regions for both the current kernel
> > and the kexec kernel, and it will also insert them into resources list.
>
> "will insert" -> "inserts".
>
> > Before the kexec kernel reboot nobody passes the old setup_data, kexec only
>
>                           ^ "reboots"                             ^ and
>
> > passes SETUP_EFI and SETUP_IMA if needed.  Thus the old setup data memory
> > are not used at all. But due to old kernel updated the kexec e820 table
>
>    ^ is                                      ^ updates
>
> > as well so kexec kernel see them as E820_TYPE_RESERVED_KERN regions, later
>
> "so kexec kernel" -> ", the kexec kernel"
>
> "see" -> "sees"
>
> ", later" -> ", and later"
>
> > the old setup_data regions will be inserted into resources list in kexec
>
> "will be" -> "are"
>
> > kernel by e820__reserve_resources().
> >
> > Note, due to no setup_data passed in for those old regions they are not
>
>                             ^ is
>
> > early reserved (by function early_reserve_memory), crashkernel memblock
>
>                                                    ^ and the
>
> > reservation will just regard them as usable memory and it could reserve
>
> "regard" -> "treat"
>
> > reserve crashkernel region overlaps with the old setup_data regions.
>
> double "reserve".
>
> "crashkernel region" -> "the crashkernel region"
>
> "overlaps" -> "which overlaps"
>
> >
> > Just like the bug I noticed here, kdump insert_resource failed because
> > e820__reserve_resources added the overlapped chunks in /proc/iomem already.
>
>                           ^ has added
> >
> > Finally, looking at the code, the old setup_data regions are not used
> > at all as no setup_data passed in by the kexec boot loader. Although
>
>                           ^ is passed
>
> > something like SETUP_PCI etc could be needed, kexec should pass
> > the info as setup_data so that kexec kernel can take care of them.
> > This should be taken care of in other separate patches if needed.
> >
> > Thus drop the useless buggy code here.
> >
> > Signed-off-by: Dave Young <dyoung@redhat.com>
> > ---
> >   arch/x86/kernel/e820.c |   16 +---------------
> >   1 file changed, 1 insertion(+), 15 deletions(-)
> >
> > Index: linux/arch/x86/kernel/e820.c
> > ===================================================================
> > --- linux.orig/arch/x86/kernel/e820.c
> > +++ linux/arch/x86/kernel/e820.c
> > @@ -1015,16 +1015,6 @@ void __init e820__reserve_setup_data(voi
> >               pa_next = data->next;
> >
> >               e820__range_update(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
> > -
> > -             /*
> > -              * SETUP_EFI and SETUP_IMA are supplied by kexec and do not need
> > -              * to be reserved.
> > -              */
> > -             if (data->type != SETUP_EFI && data->type != SETUP_IMA)
> > -                     e820__range_update_kexec(pa_data,
> > -                                              sizeof(*data) + data->len,
> > -                                              E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
> > -
> >               if (data->type == SETUP_INDIRECT) {
> >                       len += data->len;
> >                       early_memunmap(data, sizeof(*data));
> > @@ -1036,12 +1026,9 @@ void __init e820__reserve_setup_data(voi
> >
> >                       indirect = (struct setup_indirect *)data->data;
> >
> > -                     if (indirect->type != SETUP_INDIRECT) {
> > +                     if (indirect->type != SETUP_INDIRECT)
> >                               e820__range_update(indirect->addr, indirect->len,
> >                                                  E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
> > -                             e820__range_update_kexec(indirect->addr, indirect->len,
> > -                                                      E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
> > -                     }
> >               }
> >
> >               pa_data = pa_next;
> > @@ -1049,7 +1036,6 @@ void __init e820__reserve_setup_data(voi
> >       }
> >
> >       e820__update_table(e820_table);
> > -     e820__update_table(e820_table_kexec);
> >
> >       pr_info("extended physical RAM map:\n");
> >       e820__print_table("reserve setup_data");
> >
> >
>