linux-kernel - Re: [PATCH] x86/kexec: do not reserve kexec setup

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Message-ID: <20200224071419.GA18237@dhcp-128-65.nay.redhat.com>
Date:   Mon, 24 Feb 2020 15:14:19 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH] x86/kexec: do not reserve kexec setup_data in kexec e820
 table

On 02/12/20 at 07:04pm, Dave Young wrote:
> The e820 table for kexec kernel always takes setup_data as reserved.
> It is reasonable for the setup_data passed by the 1st kernel boot loader,
> for example SETUP_PCI etc.  But SETUP_EFI is used by kexec itself to
> enable EFI in 2nd kernel, also kexec setups it every time. Thus it
> is pointless to reserve kexec prepared setup_data.
> 
> 1st physical boot: no SETUP_EFI
> kexec load new kernel and prepare a SETUP_EFI setup_data, then reboot
>  -> 2nd kernel sees SETUP_EFI, reserves in both e820 and kexec e820
>     another kexec load prepare a new SETUP_EFI, then reboot
>     -> 3rd kernel has two SETUP_EFI ranges reserved
>        -> and so on..
> 
> Thus skip SETUP_EFI while reserving setup_data for kexec kernel.
> 
> Signed-off-by: Dave Young <dyoung@...hat.com>
> ---
>  arch/x86/kernel/e820.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> --- linux-x86.orig/arch/x86/kernel/e820.c
> +++ linux-x86/arch/x86/kernel/e820.c
> @@ -999,7 +999,9 @@ void __init e820__reserve_setup_data(voi
>  	while (pa_data) {
>  		data = early_memremap(pa_data, sizeof(*data));
>  		e820__range_update(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
> -		e820__range_update_kexec(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
> +		/* Skip kexec passed setup_data */
> +		if (data->type != SETUP_EFI)
> +			e820__range_update_kexec(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
>  
>  		if (data->type == SETUP_INDIRECT &&
>  		    ((struct setup_indirect *)data->data)->type != SETUP_INDIRECT) {

Ping, can someone review this? It caused fragmented memory in kexec
kernel also waste memory.

Thanks
Dave