linux-kernel - Re: [PATCH v2 0/5] Allow the trampoline to use EFI boot services RAM

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Message-ID: <CALCETrUPBSUU9syGHqfZzTA3847JQ1isBo9WKk9qQniTyPtm9g@mail.gmail.com>
Date:	Wed, 10 Aug 2016 06:21:36 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Mario Limonciello <mario_limonciello@...l.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Borislav Petkov <bp@...en8.de>,
	Matt Fleming <mfleming@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/5] Allow the trampoline to use EFI boot services RAM

On Wed, Aug 10, 2016 at 5:28 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Andy Lutomirski <luto@...nel.org> wrote:
>
>> As currently configured, my laptop cannot boot any existing kernel
>> because the real mode trampoline can't be reserved.  The ranges in
>> which it could live are rejected by the kernel: one is EFI boot
>> services data and the other is above the EBDA.
>
> Ok, so I like this series - if Matt acks it I can apply it.
>
> How urgent is it? The 'laptop does not boot' aspect worries me - how frequently
> are systems hit by this?

As far as I know, I'm the only affected user unless Mario has heard
otherwise.  I pinged the Fedora kernel maintainers and no one else has
reported this issue.  I think it needs a fully up-to-date BIOS on a
particular laptop with a non-default BIOS setting enabled that runs
Fedora (or maybe RHEL or CentOS) -- my best guess is that this is only
triggered when using Red Hat / Fedora's patched GRUB, and I have no
clue why.  I've checked, and the reported EFI memory map is different
if I boot using Fedora's GRUB and if I boot exactly the same system
off a live USB stick.

>
> The approach you chose looks sufficiently robust and straightforward to me, so it
> ought to work fine even for x86/urgent - but we can phase it into efi/core as well
> if Matt prefers that.
>

I like x86/urgent because I like to be able to boot stock kernels :)

--Andy