linux-kernel - Re: [PATCH v11 3/5] x86/boot: Add get_acpi_rsdp() to parse RSDP in cmdlien from kexec

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Date:   Wed, 14 Nov 2018 19:33:15 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Chao Fan <fanc.fnst@...fujitsu.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linux-acpi@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        keescook@...omium.org, bhe@...hat.com, msys.mizuma@...il.com,
        indou.takao@...fujitsu.com, caoj.fnst@...fujitsu.com
Subject: Re: [PATCH v11 3/5] x86/boot: Add get_acpi_rsdp() to parse RSDP in
 cmdlien from kexec

On Wed, Nov 14, 2018 at 09:54:50AM +0800, Chao Fan wrote:
> CONFIG_KEXEC is only needed in this function.
> 
> When searching RSDP, there are three methods in order:
> 1. When booting from KEXEC, 'acpi_rsdp' is added to cmdline by KEXEC,
>    so it can be parsed and used. CONFIG_KEXEC is needed here.

But theoretically acpi_rsdp can be supplied by the first kernel too,
right?

So you don't need that CONFIG_KEXEC here at all?

> >Ok, let's recap: so far, for your use case you need:
> >
> >CONFIG_MEMORY_HOTREMOVE
> >CONFIG_RANDOMIZE_BASE
> >and now
> >CONFIG_KEXEC
> >
> >So, you can clean up all that ifdeffery by defining a new config item
> >CONFIG_EARLY_PARSE_RSDP or so which depends on all those three items and
> >then you can do
> >
> >vmlinux-objs-$(CONFIG_EARLY_PARSE_RSDP) += $(obj)/acpitb.o
> >
> >and get rid of the most of the ifdeffery.

Regardless of CONFIG_KEXEC - you still need to define a CONFIG_ symbol
for your use case. We won't be parsing RSDP early on !MEMORY_HOTREMOVE
machines, which is the majority.

-- 
Regards/Gruss,
    Boris.

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