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 14:11:39 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Shannon Zhao <shannon.zhao@...aro.org>
CC:	Mark Rutland <mark.rutland@....com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	<ard.biesheuvel@...aro.org>, <leif.lindholm@...aro.org>,
	Shannon Zhao <zhaoshenglong@...wei.com>,
	<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>, <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, Shannon Zhao wrote:
> On 2016/1/19 21:13, Mark Rutland wrote:
> > On Tue, Jan 19, 2016 at 12:23:17PM +0000, Stefano Stabellini wrote:
> > > >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 take it that means that any memory carved out for Xen itself is
> > described/discovered via a separate mechanism? How does that work
> 
> For Xen hypervisor booting on UEFI, it get the EFI memory map through the
> similar way like Linux, e.g. call EFI_BOOT_SERVICES.GetMemoryMap().
> For Dom0, Xen will create a new EFI memory map for Dom0.
> 
> See [PATCH v3 52/62] arm/acpi: Prepare EFI memory descriptor for Dom0
> http://lists.xen.org/archives/html/xen-devel/2015-11/msg01884.html

Ah! That patch is not upstream yet, that's why I thought that something
was off. Listen to Shannon, don't listen to me :-)