linux-kernel - Re: [PATCH] x86/kexec: do not update E820 kexec table for setup

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Date: Thu, 21 Mar 2024 10:56:20 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: Dave Young <dyoung@...hat.com>, <x86@...nel.org>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
	<kexec@...ts.infradead.org>, Baoquan He <bhe@...hat.com>, Eric Biederman
	<ebiederm@...ssion.com>
Subject: Re: [PATCH] x86/kexec: do not update E820 kexec table for setup_data

Hi Dave,

Some nitpicking in changelog:

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@...hat.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");
> 
>