linux-kernel - Re: [tip: x86/kdump] x86/kexec: Do not reserve EFI setup

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Message-ID: <20200225014912.GA13800@dhcp-128-65.nay.redhat.com>
Date:   Tue, 25 Feb 2020 09:49:12 +0800
From:   Dave Young <dyoung@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        x86 <x86@...nel.org>
Subject: Re: [tip: x86/kdump] x86/kexec: Do not reserve EFI setup_data in the
 kexec e820 table

On 02/24/20 at 10:51am, tip-bot2 for Dave Young wrote:
> The following commit has been merged into the x86/kdump branch of tip:
> 
> Commit-ID:     8efbc518b884e1db2dd6a6fce62d0112ab871dcf
> Gitweb:        https://git.kernel.org/tip/8efbc518b884e1db2dd6a6fce62d0112ab871dcf
> Author:        Dave Young <dyoung@...hat.com>
> AuthorDate:    Wed, 12 Feb 2020 19:04:24 +08:00
> Committer:     Borislav Petkov <bp@...e.de>
> CommitterDate: Mon, 24 Feb 2020 11:41:57 +01:00
> 
> x86/kexec: Do not reserve EFI setup_data in the kexec e820 table
> 
> The e820 table for the kexec kernel unconditionally marks setup_data as
> reserved because the second kernel can reuse setup_data passed by the
> 1st kernel's boot loader, for example SETUP_PCI marked regions like PCI
> BIOS, etc.
> 
> SETUP_EFI types, however, are used by kexec itself to enable EFI in the
> 2nd kernel. Thus, it is pointless to add this type of setup_data to the
> kexec e820 table as reserved.
> 
> IOW, what happens is this:
> 
>   -  1st physical boot: no SETUP_EFI.
> 
>   - kexec loads a new kernel and prepares a SETUP_EFI setup_data blob, then
>   reboots the machine.
> 
>   - 2nd kernel sees SETUP_EFI, reserves it both in the e820 and in the
>   kexec e820 table.
> 
>   - If another kexec load is executed, it prepares a new SETUP_EFI blob and
>   then reboots the machine into the new kernel.
> 
>   5. The 3rd kexec-ed kernel has two SETUP_EFI ranges reserved. And so on...
> 
> Thus skip SETUP_EFI while reserving setup_data in the e820_table_kexec
> table because it is not needed.
> 
>  [ bp: Heavily massage commit message, shorten line and improve comment. ]

Boris, thanks for the amending and log massage.
I was hesitating to break the long line or not and then I choosed
leaving it as is.  Both are not very good and either of them is fine to me.

Thanks
Dave