linux-kernel - Re: [PATCH] x86/boot: EFI_MIXED should not prohibit loading above 4G

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Message-ID: <CADknwL7Jeh82W3=rEqGqh=37zpqhmMuP1jy+DDq9vb2gQ+9hzg@mail.gmail.com>
Date:	Mon, 9 Jun 2014 14:18:54 +0100
From:	Matt Fleming <matt@...sole-pimps.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-efi@...r.kernel.org,
	Matt Fleming <matt.fleming@...el.com>,
	Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH] x86/boot: EFI_MIXED should not prohibit loading above 4G

On 9 June 2014 13:54, Vivek Goyal <vgoyal@...hat.com> wrote:
> Hi Matt,
>
> So with new kexec syscall I have written 64bit bzImage loader. For now
> I would like to detect this situation and disable loading and once
> 32bit loader gets implemented it can take care of loading bzImage below
> 4G.

What situation do you want to detect? You want to detect when it's
impossible to load a kernel above 4G in the kexec path because you're
booting with 32-bit EFI firmware?

> So how do I find out if EFI is 32bit.

efi_enabled(EFI_64BIT) will tell you that, but you probably also want
to check that EFI runtime services are actually usable with
efi_enabled(EFI_RUNTIME_SERVICES) since if they're not, you'll never
call into the firmware so it doesn't matter where you load the kernel
(this may happen with "noefi" kernel parameter).
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