linux-kernel - Re: [PATCH v2 12/16] ARM: Xen: Document UEFI support on Xen ARM virtual platforms

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Date:	Tue, 19 Jan 2016 12:23:17 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Shannon Zhao <zhaoshenglong@...wei.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<ard.biesheuvel@...aro.org>, <leif.lindholm@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<stefano.stabellini@...rix.com>, <david.vrabel@...rix.com>,
	<catalin.marinas@....com>, <will.deacon@....com>,
	<julien.grall@...rix.com>, <xen-devel@...ts.xen.org>,
	<devicetree@...r.kernel.org>, <linux-efi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <shannon.zhao@...aro.org>,
	<peter.huangpeng@...wei.com>, Jan Beulich <JBeulich@...ell.com>,
	Ian Campbell <Ian.Campbell@...rix.com>
Subject: Re: [PATCH v2 12/16] ARM: Xen: Document UEFI support on Xen ARM
 virtual platforms

On Tue, 19 Jan 2016, Mark Rutland wrote:
> On Tue, Jan 19, 2016 at 06:25:25PM +0800, Shannon Zhao wrote:
> > >> We don't do this in Documentation/arm/uefi.txt, and I don't see why we
> > >> should do so here.
> > >>
> > >> Does Xen handle arbitrary size memory map descriptors? I'm not sure what
> > >> new information might be passed in future additions to the descriptor
> > >> format, and I'm not sure what should happen in the Dom0 case.
> > > 
> > > Xen passes to Dom0 the memory map in the same format as the native
> > > memory map.
> 
> Does Xen parse or modify the EFI memory map in any way?

Xen:
- calls EFI_BOOT_SERVICES.GetMemoryMap()
- takes note of the memory regions for its own usage
- create the fdt notes, including efi-mmap-start, with a pointer to it


> Does it pass the raw values returned by EFI_BOOT_SERVICES.GetMemoryMap()
> through to the xen,uefi-* properties, or does is make any static
> assumptions about what the values will be?

It just passes the raw values.


> I'm trying to get a feeling for what the behaviour will be if/when a
> version of the EFI spec expands the memory map format.

Linux is likely to get the memory map in the same format as it's
provided on native.