linux-kernel - Re: efi_enabled(EFI

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Message-ID: <alpine.DEB.2.10.1604291547130.3312@sstabellini-ThinkPad-X260>
Date:	Fri, 29 Apr 2016 15:58:47 +0100 (BST)
From:	Stefano Stabellini <sstabellini@...nel.org>
To:	Matt Fleming <matt@...eblueprint.co.uk>
cc:	Stefano Stabellini <sstabellini@...nel.org>,
	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>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: efi_enabled(EFI_PARAVIRT) use

On Fri, 29 Apr 2016, Matt Fleming wrote:
> On Fri, 29 Apr, at 11:34:45AM, Stefano Stabellini wrote:
> > On Fri, 29 Apr 2016, Ingo Molnar wrote:
> > > Also, it would be nice to have all things EFI in a single tree, the conflicts are 
> > > going to be painful! There's very little reason not to carry this kind of commit:
> > > 
> > >  arch/arm/xen/enlighten.c           |  6 +++++
> > >  drivers/firmware/efi/arm-runtime.c | 17 +++++++++-----
> > >  drivers/firmware/efi/efi.c         | 45 ++++++++++++++++++++++++++++++++------
> > >  3 files changed, 56 insertions(+), 12 deletions(-)
> > > 
> > > in the EFI tree.
> > 
> > That's true. I'll drop this commit from xentip and let Matt pick it up
> > or request changes as he sees fit.
> 
> One small change I think would be sensible to make is to expand
> EFI_PARAVIRT into a few more bits to clearly indicate the quirks on
> Xen, and in the process, to delete EFI_PARAVIRT.
> 
> That should address Ingo's major concern, and also make it much easier
> to rework the code in a piecemeal fashion.
> 
> Could somebody enumerate the things that make Xen (dom0) different on
> arm* compared with bare metal EFI boot? The list I made for x86 was,
> 
>   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
> 
> The first maps to not setting EFI_MEMMAP, the second to not setting
> EFI_RUNTIME. If we add EFI_ALREADY_VIRTUAL and EFI_FW_VENDOR_INVISIBLE
> to efi.flags that should cover everything on x86. Does arm* require
> anything else?

Xen on ARM is different, the impact should be limited:

- there are no BootServices (ExitBootServices has already been called)
- RuntimeServices go via hypercalls

The UEFI memory map is still available at an address specified on device
tree like on native, but the compatibility string is different
("xen,uefi-mmap-start") to clarify that we are booting on Xen rather
than native.

That's pretty much it, Shannon please confirm.