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

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Message-ID: <20140609141512.GA22049@redhat.com>
Date:	Mon, 9 Jun 2014 10:15:12 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
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 Mon, Jun 09, 2014 at 02:18:54PM +0100, Matt Fleming wrote:
> 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?

Yes.

> 
> > 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).

Ok, thanks. Or I can check whether EFI run time map is there or not. I am
assuming that efi runtime services are not enabled, then run time map
will not be there either.

Thanks
Vivek
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