linux-kernel - Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on kexec-ed kernel

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Message-ID: <cc2c1dbe-4fb3-fb7d-0540-c04734fc15cb@ce.jp.nec.com>
Date:   Mon, 15 Apr 2019 07:01:54 +0000
From:   Junichi Nomura <j-nomura@...jp.nec.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Dave Young <dyoung@...hat.com>,
        Chao Fan <fanc.fnst@...fujitsu.com>,
        Baoquan He <bhe@...hat.com>, Kairui Song <kasong@...hat.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] x86/boot: Use efi_setup_data for searching RSDP on
 kexec-ed kernel

On 4/12/19 10:35 PM, Borislav Petkov wrote:
> On Fri, Apr 12, 2019 at 10:49:56AM +0200, Borislav Petkov wrote:
>> Now I need to go figure out whether there's a reliable way to know in
>> the kexec kernel that it *is* a kexec kernel.
> 
> Actually, thinking about this more, we don't need to know whether the
> kernel was kexeced or not. Why?
> 
> Because if it is kexec'ed, kexec(1) passes the required info in
> setup_data. Now, if for whatever reason the kexec'ed kernel fails to
> parse that EFI info and get the systab to figure out the RDSP, then it
> doesn't have any other choice but fail booting.
> 
> Because there's no way it can figure out where the EFI runtime has been
> mapped and recover by finding the RDSP from there.
> 
> So I think we're perfectly fine with the old approach:
> 
>         if (!pa)
>                 pa = kexec_get_rsdp_addr();
> 
>         if (!pa)
>                 pa = efi_get_rsdp_addr();

OK. Then I'll go back to v3 and make sure to hang when
something is wrong during kexec boot on EFI system.

-- 
Jun'ichi Nomura, NEC Corporation / NEC Solution Innovators, Ltd.