linux-kernel - Re: efi_enabled(EFI

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Message-ID: <20160429092651.GD2839@codeblueprint.co.uk>
Date:	Fri, 29 Apr 2016 10:26:51 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Xen Devel <Xen-devel@...ts.xensource.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Shannon Zhao <shannon.zhao@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: efi_enabled(EFI_PARAVIRT) use

On Fri, 29 Apr, at 10:25:02AM, Borislav Petkov wrote:
> On Fri, Apr 29, 2016 at 08:39:36AM +0200, Ingo Molnar wrote:
> > With considerable pain we just got rid of paravirt_enabled() in the
> > x86 tree, and Xen is now reintroducing it in the EFI code.
> 
> I think Matt is working towards removing EFI_PARAVIRT but he'll comment
> himself when he wakes up... :)

Yeah, I haven't actually got around to dropping EFI_PARAVIRT yet but
since it's basically used to skip certain initialisation operations on
boot I figured we could just provide empty stub functions as part of
struct efi (probably).

The concerns Ingo voiced about EFI_PARAVIRT being a catch-all flag are
very true.

Incidentally kexec and arm64 would need a similar stub functions if we
move more EFI runtime setup code to drivers/firmware/efi, which is my
long-term plan, since neither can call SetVirtualAddressMap().

On x86, I think EFI_PARAVIRT is code for,

  1. Has no EFI memory map
  2. Runtime regions do not need to be mapped
  3. Cannot call SetVirtualAddressMap()
  4. /sys/firmware/efi/fw_vendor is invisible

1. and 2. should be covered by never setting EFI_MEMMAP and
EFI_RUNTIME_SERVICES in efi.flags. We have no bits for 3. and 4. yet.