[RFC v2] ARM VM System Specification

[RFC v2] ARM VM System Specification

[Christoffer Dall]

ARM VM System Specification
===========================

Goal
----
The goal of this spec is to allow suitably-built OS images to run on
all ARM virtualization solutions, such as KVM or Xen.

Recommendations in this spec are valid for aarch32 and aarch64 alike, and
they aim to be hypervisor agnostic.

Note that simply adhering to the SBSA [2] is not a valid approach, for
example because the SBSA mandates EL2, which will not be available for
VMs.  Further, this spec also covers the aarch32 execution mode, not
covered in the SBSA.


Image format
------------
The image format, as presented to the VM, needs to be well-defined in
order for prepared disk images to be bootable across various
virtualization implementations.

The raw disk format as presented to the VM must be partitioned with a
GUID Partition Table (GPT).  The bootable software must be placed in the
EFI System Partition (ESP), using the UEFI removable media path, and
must be an EFI application complying to the UEFI Specification 2.4
Revision A [6].

The ESP partition's GPT entry's partition type GUID must be
C12A7328-F81F-11D2-BA4B-00A0C93EC93B and the file system must be
formatted as FAT32/vfat as per Section 12.3.1.1 in [6].

The removable media path is \EFI\BOOT\BOOTARM.EFI for the aarch32
execution state and is \EFI\BOOT\BOOTAA64.EFI for the aarch64 execution
state as specified in Section 3.3 (3.3 (Boot Option Variables Default Boot
Behavior) and 3.4.1.1 (Removable Media Boot Behavior) in [6].

This ensures that tools for both Xen and KVM can load a binary UEFI
firmware which can read and boot the EFI application in the disk image.

A typical scenario will be GRUB2 packaged as an EFI application, which
mounts the system boot partition and boots Linux.


Virtual Firmware
----------------
The VM system must be UEFI compliant in order to be able to boot the EFI
application in the ESP.  It is recommended that this is achieved by
loading a UEFI binary as the first software executed by the VM, which
then executes the EFI application.  The UEFI implementation should be
compliant with UEFI Specification 2.4 Revision A [6] or later.

This document strongly recommends that the VM implementation supports
persistent environment storage for virtual firmware implementation in
order to ensure probable use cases such as adding additional disk images
to a VM or running installers to perform upgrades.

This document strongly recommends that VM implementations implement
persistent variable storage for their UEFI implementation.  Persistent
variable storage shall be a property of a VM instance, but shall not be
stored as part of a portable disk image.  Portable disk images shall
conform to the UEFI removable disk requirements from the UEFI spec and
cannot rely on on a pre-configured UEFI environment.

The binary UEFI firmware implementation should not be distributed as
part of the VM image, but is specific to the VM implementation.


Hardware Description
--------------------
The VM system must be UEFI compliant and therefore the UEFI system table
will provide a means to access hardware description data.

The VM implementation must provide through its UEFI implementation:

  a complete FDT which describes the entire VM system and will boot
  mainline kernels driven by device tree alone

For more information about the arm and arm64 boot conventions, see
Documentation/arm/Booting and Documentation/arm64/booting.txt in the
Linux kernel source tree.

For more information about UEFI booting, see [4] and [5].


VM Platform
-----------
The specification does not mandate any specific memory map.  The guest
OS must be able to enumerate all processing elements, devices, and
memory through HW description data (FDT) or a bus-specific
mechanism such as PCI.

If aarch64 physical CPUs implement support for the aarch32 execution
state in EL1 and EL0 execution, it is recommended that the VM
implementation supports booting the VM at EL1 in both aarch32 and
aarch64 execution states.

The virtual hardware platform must provide a number of mandatory
peripherals:

  Serial console:  The platform should provide a console,
  based on an emulated pl011, a virtio-console, or a Xen PV console.

  An ARM Generic Interrupt Controller v2 (GICv2) [3] or newer.  GICv2
  limits the the number of virtual CPUs to 8 cores, newer GIC versions
  removes this limitation.

  The ARM virtual timer and counter should be available to the VM as
  per the ARM Generic Timers specification in the ARM ARM [1].

It is strongly recommended that the VM implementation provides a
hotpluggable bus to support hotplug of at least block and network
devices.  Suitable buses include a virtual PCIe bus and the Xen PV bus.

For the VM image to be compliant with this spec, the following applies
for the guest OS in the VM image:

  The guest OS must include support for pl011 UART, virtio-console, and
  the Xen PV console.

  The guest OS must include support for GICv2 and any available newer
  version of the GIC architecture to maintain compatibility with older
  VM implementations.

  It is strongly recommended to include support for all available
  (block, network, console, balloon) virtio-pci, virtio-mmio, and Xen PV
  drivers in the guest OS kernel or initial ramdisk.


Other common peripherals for block devices, networking, and more can
(and typically will) be provided, but OS software written and compiled
to run on ARM VMs cannot make any assumptions about which variations
of these should exist or which implementation they use (e.g. VirtIO or
Xen PV).  See "Hardware Description" above.


Changes from previous versions of this RFC
------------------------------------------
Changes v1-v2:
 - Clearly specify that the guest must support the pl011,
   virtio-console, and Xen PV console.  (Note that it was discussed to
   mandate a pl011 during Linaro Connect Asia 2014, but that was under the
   impression that the SBSA specification was an output-only no-irq
   serial port, which is not the case.  The only two benefits from
   mandating a specific serial type was to handle "console=ttyAMA0"
   kernel command line parameters and earlyprintk; Grant Likely has
   submitted patches to avoid the need for "console=" parameters, and
   Rob Herring has submitted patches for paravirtualized earlyprintk
   consoles.)
 - Reference EFI specification for bootable paths.
 - Remove discussion on ACPI boot methods and do not suggest ACPI
   support in VMs.
 - Add specification about UEFI persistent variable storage and
   portability.


References
----------
[1]: The ARM Architecture Reference Manual, ARMv8, Issue A.b
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html

[2]: ARM Server Base System Architecture
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0029/index.html

[3]: The ARM Generic Interrupt Controller Architecture Specifications v2.0
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html

[4]: http://www.secretlab.ca/archives/27

[5]: https://git.linaro.org/people/leif.lindholm/linux.git/blob/refs/heads/uefi-for-upstream:/Documentation/arm/uefi.txt

[6]: UEFI Specification 2.4 Revision A
http://www.uefi.org/sites/default/files/resources/2_4_Errata_A.pdf

[RFC v2] ARM VM System Specification

[Olof Johansson]

On Fri, Mar 28, 2014 at 11:45 AM, Christoffer Dall
<christoffer.dall@linaro.org> wrote:
> ARM VM System Specification
> ===========================

[not quoting the whole spec here]

This looks very sane to me, and aligns very well with non-virtualized images.

For what it's worth, even though it's not a patch:

Acked-by: Olof Johansson <olof@lixom.net>

What's the plan on how to lock this in? Where's this document going to
live? In the kernel sources under Documentation/, or external?


-Olof

[RFC v2] ARM VM System Specification

[Christoffer Dall]

On Sun, Mar 30, 2014 at 03:10:50PM -0700, Olof Johansson wrote:
> On Fri, Mar 28, 2014 at 11:45 AM, Christoffer Dall
> <christoffer.dall@linaro.org> wrote:
> > ARM VM System Specification
> > ===========================
> 
> [not quoting the whole spec here]
> 
> This looks very sane to me, and aligns very well with non-virtualized images.
> 
> For what it's worth, even though it's not a patch:
> 
> Acked-by: Olof Johansson <olof@lixom.net>

Thanks, appreciate it.

> 
> What's the plan on how to lock this in? Where's this document going to
> live? In the kernel sources under Documentation/, or external?
> 

There were talks during LCA14 about publishing it as a Linaro
white-paper, but I would like it to be hosted by the open-source
projects that relate to it, for example the Linux kernel under
Documentaiton/ to represent both the guest and KVM side, and the Xen
sources too.

However, that may be a pain to update so the preferred method could be
to host it in either its current form (clear-text) or publish some
versioned PDF somewhere and simply point to it from the compliant
software pieces.

Suggestions or input welcome.

-Christoffer

[RFC v2] ARM VM System Specification

[Ian Campbell]

On Mon, 2014-03-31 at 10:26 -0700, Christoffer Dall wrote:
> However, that may be a pain to update

Very much, and there would be nothing worse than having multiple
divergent copies of the spec.

>  so the preferred method could be
> to host it in either its current form (clear-text) or publish some
> versioned PDF somewhere and simply point to it from the compliant
> software pieces.

I think that would be best.

I'm at a loss to suggest a suitable neutral home though I'm afraid.

Ian.

[RFC v2] ARM VM System Specification

[Michael Casadevall]

-----BEGIN PGP SIGNED MESSAGE-----
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On 04/01/2014 05:49 AM, Ian Campbell wrote:
> On Mon, 2014-03-31 at 10:26 -0700, Christoffer Dall wrote:
>> However, that may be a pain to update
> 
> Very much, and there would be nothing worse than having multiple 
> divergent copies of the spec.
> 
>> so the preferred method could be to host it in either its current
>> form (clear-text) or publish some versioned PDF somewhere and
>> simply point to it from the compliant software pieces.
> 
> I think that would be best.
> 
> I'm at a loss to suggest a suitable neutral home though I'm
> afraid.
> 

I agree with formal PDF (or TeX/plain text) releases + versioning;
something I can print out and hit people with always works great for
spec compliance.

On the topic of hosting, if Linaro itself isn't neutral enough, what
about under the Linux Foundation? They already host a bunch of
standards like the FHS.
Michael
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[RFC v2] ARM VM System Specification

[Grant Likely]

Start with Linaro publishing it. It can always be moved to another
venue if someone dislikes Linaro having maintainership.

g.


On Tue, Apr 1, 2014 at 10:57 AM, Michael Casadevall
<michael.casadevall@linaro.org> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
>
>
> On 04/01/2014 05:49 AM, Ian Campbell wrote:
>> On Mon, 2014-03-31 at 10:26 -0700, Christoffer Dall wrote:
>>> However, that may be a pain to update
>>
>> Very much, and there would be nothing worse than having multiple
>> divergent copies of the spec.
>>
>>> so the preferred method could be to host it in either its current
>>> form (clear-text) or publish some versioned PDF somewhere and
>>> simply point to it from the compliant software pieces.
>>
>> I think that would be best.
>>
>> I'm at a loss to suggest a suitable neutral home though I'm
>> afraid.
>>
>
> I agree with formal PDF (or TeX/plain text) releases + versioning;
> something I can print out and hit people with always works great for
> spec compliance.
>
> On the topic of hosting, if Linaro itself isn't neutral enough, what
> about under the Linux Foundation? They already host a bunch of
> standards like the FHS.
> Michael
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> Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
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> -----END PGP SIGNATURE-----

[RFC v2] ARM VM System Specification

[Christoffer Dall]

On Fri, Mar 28, 2014 at 11:45:17AM -0700, Christoffer Dall wrote:
> ARM VM System Specification
> ===========================
> 

I didn't receive a lot of comments on this one, I take this to mean that
most people are happy with the content.  If not, now is the time to
speak up, otherwise we'll be taking steps to try and publish this
slightly more formally.

Thanks,
-Christoffer

[RFC v2] ARM VM System Specification

[Grant Likely]

On Tue, 29 Apr 2014 07:42:06 -0700, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> On Fri, Mar 28, 2014 at 11:45:17AM -0700, Christoffer Dall wrote:
> > ARM VM System Specification
> > ===========================
> > 
> 
> I didn't receive a lot of comments on this one, I take this to mean that
> most people are happy with the content.  If not, now is the time to
> speak up, otherwise we'll be taking steps to try and publish this
> slightly more formally.

Yes, I'm happy with it.

g.

[RFC v2] ARM VM System Specification

[Peter Maydell]

On 28 March 2014 18:45, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> ARM VM System Specification
> ===========================
>

> The virtual hardware platform must provide a number of mandatory
> peripherals:
>
>   Serial console:  The platform should provide a console,
>   based on an emulated pl011, a virtio-console, or a Xen PV console.
>
>   An ARM Generic Interrupt Controller v2 (GICv2) [3] or newer.  GICv2
>   limits the the number of virtual CPUs to 8 cores, newer GIC versions
>   removes this limitation.
>
>   The ARM virtual timer and counter should be available to the VM as
>   per the ARM Generic Timers specification in the ARM ARM [1].

I just noticed that this doesn't mandate that the platform
provides an RTC. As I understand it, the UEFI spec mandates
that there's an RTC (could somebody more familiar with UEFI
than me confirm/deny that?) so we should probably put one here.

Suggested wording:

 RTC: The platform should provide a real time clock, based
 on an emulated pl031 or mc146818.

and in the guest-support section later:

 The guest OS must include support for pl031 and mc146818 RTC.

(QEMU is going to provide a PL031, because that's the standard
ARM primecell device for this and it's what's in the vexpress.
kvmtool looks like it's going to provide mc146818, because
that's the standard x86 RTC and kvmtool happens to already
emulate that.)

thanks
-- PMM

[RFC v2] ARM VM System Specification

[Ian Campbell]

On Tue, 2014-06-10 at 15:42 +0100, Peter Maydell wrote:
> On 28 March 2014 18:45, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> > ARM VM System Specification
> > ===========================
> >
> 
> > The virtual hardware platform must provide a number of mandatory
> > peripherals:
> >
> >   Serial console:  The platform should provide a console,
> >   based on an emulated pl011, a virtio-console, or a Xen PV console.
> >
> >   An ARM Generic Interrupt Controller v2 (GICv2) [3] or newer.  GICv2
> >   limits the the number of virtual CPUs to 8 cores, newer GIC versions
> >   removes this limitation.
> >
> >   The ARM virtual timer and counter should be available to the VM as
> >   per the ARM Generic Timers specification in the ARM ARM [1].
> 
> I just noticed that this doesn't mandate that the platform
> provides an RTC. As I understand it, the UEFI spec mandates
> that there's an RTC (could somebody more familiar with UEFI
> than me confirm/deny that?) so we should probably put one here.

Isn't that already done transitively via the requirement to provide a
UEFI environment?

I thought the RTC was exposed via UEFI Runtime Service, in which case
it's mostly a hypervisor internal issue how time is provided to the
(hypervisor provided) UEFI implementation, the guest OS just uses the
runtime services interfaces.

Given that do we also need to standardise on a guest OS visible clock
device too? I'm not sure if we do or not, but if yes then I have a
couple of comments on the suggested wording (you can probably guess what
they are going to be...):

> Suggested wording:
> 
>  RTC: The platform should provide a real time clock, based
>  on an emulated pl031 or mc146818.

We would need to include the Xen PV wallclock here too.

> and in the guest-support section later:
> 
>  The guest OS must include support for pl031 and mc146818 RTC.

and here.

Ian.

[RFC v2] ARM VM System Specification

[Paolo Bonzini]

Il 10/06/2014 16:42, Peter Maydell ha scritto:
>  The guest OS must include support for pl031 and mc146818 RTC.
>
> (QEMU is going to provide a PL031, because that's the standard
> ARM primecell device for this and it's what's in the vexpress.
> kvmtool looks like it's going to provide mc146818, because
> that's the standard x86 RTC and kvmtool happens to already
> emulate that.)

Why can't kvmtool add pl031 support?  mc146818 is quite complicated to 
emulate efficiently (without waking up once a second or more).

Paolo

[RFC v2] ARM VM System Specification

[Christopher Covington]

Hi Peter,

On 06/10/2014 10:42 AM, Peter Maydell wrote:
> On 28 March 2014 18:45, Christoffer Dall <christoffer.dall@linaro.org> wrote:
>> ARM VM System Specification
>> ===========================
>>
> 
>> The virtual hardware platform must provide a number of mandatory
>> peripherals:
>>
>>   Serial console:  The platform should provide a console,
>>   based on an emulated pl011, a virtio-console, or a Xen PV console.
>>
>>   An ARM Generic Interrupt Controller v2 (GICv2) [3] or newer.  GICv2
>>   limits the the number of virtual CPUs to 8 cores, newer GIC versions
>>   removes this limitation.
>>
>>   The ARM virtual timer and counter should be available to the VM as
>>   per the ARM Generic Timers specification in the ARM ARM [1].
> 
> I just noticed that this doesn't mandate that the platform
> provides an RTC. As I understand it, the UEFI spec mandates
> that there's an RTC (could somebody more familiar with UEFI
> than me confirm/deny that?) so we should probably put one here.

Pardon my ignorance, but what exactly disqualifies Generic Timer
implementations from being used as Real Time Clocks?

Thanks,
Christopher

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted by the Linux Foundation.

[RFC v2] ARM VM System Specification

[Peter Maydell]

On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
> On 06/10/2014 10:42 AM, Peter Maydell wrote:
>> I just noticed that this doesn't mandate that the platform
>> provides an RTC. As I understand it, the UEFI spec mandates
>> that there's an RTC (could somebody more familiar with UEFI
>> than me confirm/deny that?) so we should probably put one here.
>
> Pardon my ignorance, but what exactly disqualifies Generic Timer
> implementations from being used as Real Time Clocks?

So my naive view was that an RTC actually had to have
support for dealing with real (wall) clock time, ie
knowing it's 2014 and not 1970. The generic timers are
just timers. Or am I wrong and UEFI doesn't really
require that?

It's also handy if you're booting Linux directly without
UEFI, since it means you can actually have a /dev/rtc0
(and QEMU's implementation at least will correctly give
you the time based on the host's RTC).

thanks
-- PMM

[RFC v2] ARM VM System Specification

[Paolo Bonzini]

Il 10/06/2014 20:08, Peter Maydell ha scritto:
> On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
>> On 06/10/2014 10:42 AM, Peter Maydell wrote:
>>> I just noticed that this doesn't mandate that the platform
>>> provides an RTC. As I understand it, the UEFI spec mandates
>>> that there's an RTC (could somebody more familiar with UEFI
>>> than me confirm/deny that?) so we should probably put one here.
>>
>> Pardon my ignorance, but what exactly disqualifies Generic Timer
>> implementations from being used as Real Time Clocks?
>
> So my naive view was that an RTC actually had to have
> support for dealing with real (wall) clock time, ie
> knowing it's 2014 and not 1970. The generic timers are
> just timers. Or am I wrong and UEFI doesn't really
> require that?

The real-time clock provides four UEFI runtime services (GetTime, 
SetTime, GetWakeupTime, SetWakeupTime).  The spec says that you can 
return EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be 
retrieved/set due to a hardware error", but I don't think this is enough 
to make these two optional.  By comparison, GetWakeupTime/SetWakeupTime 
can also return EFI_UNSUPPORTED.

So I agree that the RTC is required in UEFI.

Paolo

[RFC v2] ARM VM System Specification

[Paolo Bonzini]

Il 10/06/2014 20:56, Paolo Bonzini ha scritto:
> Il 10/06/2014 20:08, Peter Maydell ha scritto:
>> On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
>>> On 06/10/2014 10:42 AM, Peter Maydell wrote:
>>>> I just noticed that this doesn't mandate that the platform
>>>> provides an RTC. As I understand it, the UEFI spec mandates
>>>> that there's an RTC (could somebody more familiar with UEFI
>>>> than me confirm/deny that?) so we should probably put one here.
>>>
>>> Pardon my ignorance, but what exactly disqualifies Generic Timer
>>> implementations from being used as Real Time Clocks?
>>
>> So my naive view was that an RTC actually had to have
>> support for dealing with real (wall) clock time, ie
>> knowing it's 2014 and not 1970. The generic timers are
>> just timers. Or am I wrong and UEFI doesn't really
>> require that?
>
> The real-time clock provides four UEFI runtime services (GetTime,
> SetTime, GetWakeupTime, SetWakeupTime).  The spec says that you can
> return EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be
> retrieved/set due to a hardware error", but I don't think this is enough
> to make these two optional.  By comparison, GetWakeupTime/SetWakeupTime
> can also return EFI_UNSUPPORTED.
>
> So I agree that the RTC is required in UEFI.

... that said, just like I thought was the case for the serial console, 
do we need to specify the exact hardware models?

We can just say that the VM can expect UEFI boot and runtime services to 
work.  This includes variable services, time services, the serial 
console protocols and more.  It's up to the implementation to provide 
enough devices to support the firmware, and it's out of this spec's 
scope to specify the firmware's implementation.

Paolo

[RFC v2] ARM VM System Specification

[Paolo Bonzini]

Il 10/06/2014 20:56, Paolo Bonzini ha scritto:
> Il 10/06/2014 20:08, Peter Maydell ha scritto:
>> On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
>>> On 06/10/2014 10:42 AM, Peter Maydell wrote:
>>>> I just noticed that this doesn't mandate that the platform
>>>> provides an RTC. As I understand it, the UEFI spec mandates
>>>> that there's an RTC (could somebody more familiar with UEFI
>>>> than me confirm/deny that?) so we should probably put one here.
>>>
>>> Pardon my ignorance, but what exactly disqualifies Generic Timer
>>> implementations from being used as Real Time Clocks?
>>
>> So my naive view was that an RTC actually had to have
>> support for dealing with real (wall) clock time, ie
>> knowing it's 2014 and not 1970. The generic timers are
>> just timers. Or am I wrong and UEFI doesn't really
>> require that?
>
> The real-time clock provides four UEFI runtime services (GetTime,
> SetTime, GetWakeupTime, SetWakeupTime).  The spec says that you can
> return EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be
> retrieved/set due to a hardware error", but I don't think this is enough
> to make these two optional.  By comparison, GetWakeupTime/SetWakeupTime
> can also return EFI_UNSUPPORTED.
>
> So I agree that the RTC is required in UEFI.

... that said, just like I thought was the case for the serial console, 
do we need to specify the exact hardware models?

We can just say that the VM can expect UEFI boot and runtime services to 
work.  This includes variable services, time services, the serial 
console protocols and more.  It's up to the implementation to provide 
enough devices to support the firmware, and it's out of this spec's 
scope to specify the firmware's implementation.

I think even the serial devices should be removed.

Paolo

[RFC v2] ARM VM System Specification

[Christoffer Dall]

On Tue, Jun 10, 2014 at 09:18:34PM +0200, Paolo Bonzini wrote:
> Il 10/06/2014 20:56, Paolo Bonzini ha scritto:
> >Il 10/06/2014 20:08, Peter Maydell ha scritto:
> >>On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
> >>>On 06/10/2014 10:42 AM, Peter Maydell wrote:
> >>>>I just noticed that this doesn't mandate that the platform
> >>>>provides an RTC. As I understand it, the UEFI spec mandates
> >>>>that there's an RTC (could somebody more familiar with UEFI
> >>>>than me confirm/deny that?) so we should probably put one here.
> >>>
> >>>Pardon my ignorance, but what exactly disqualifies Generic Timer
> >>>implementations from being used as Real Time Clocks?
> >>
> >>So my naive view was that an RTC actually had to have
> >>support for dealing with real (wall) clock time, ie
> >>knowing it's 2014 and not 1970. The generic timers are
> >>just timers. Or am I wrong and UEFI doesn't really
> >>require that?
> >
> >The real-time clock provides four UEFI runtime services (GetTime,
> >SetTime, GetWakeupTime, SetWakeupTime).  The spec says that you can
> >return EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be
> >retrieved/set due to a hardware error", but I don't think this is enough
> >to make these two optional.  By comparison, GetWakeupTime/SetWakeupTime
> >can also return EFI_UNSUPPORTED.
> >
> >So I agree that the RTC is required in UEFI.
> 
> ... that said, just like I thought was the case for the serial
> console, do we need to specify the exact hardware models?
> 
> We can just say that the VM can expect UEFI boot and runtime
> services to work.  This includes variable services, time services,
> the serial console protocols and more.  It's up to the
> implementation to provide enough devices to support the firmware,
> and it's out of this spec's scope to specify the firmware's
> implementation.
> 
> I think even the serial devices should be removed.
> 
The problem is that the most common user problem with ARM VMs are that
they boot the thing, and then get no output.  So we wanted some way to
make sure we know that the kernel should be able to print to a console.

UEFI does provide DBG2 output, but that's only during boot time service
(so I'm told), and we need to mandate something that will work  when
the kernel boots.

If kernels actually do use the UEFI runtime services and have no need
for direct access to an RTC when runing in a UEFI compliant system, then
I agree with not specifying the hardware details.

-Christoffer

[RFC v2] ARM VM System Specification

[Paolo Bonzini]

Il 11/06/2014 08:54, Christoffer Dall ha scritto:
> The problem is that the most common user problem with ARM VMs are that
> they boot the thing, and then get no output.  So we wanted some way to
> make sure we know that the kernel should be able to print to a console.
>
> UEFI does provide DBG2 output, but that's only during boot time service
> (so I'm told), and we need to mandate something that will work  when
> the kernel boots.

Doh, indeed the console is not part of run-time services (so it's not 
even available for earlyprintk).

> If kernels actually do use the UEFI runtime services and have no need
> for direct access to an RTC when runing in a UEFI compliant system, then
> I agree with not specifying the hardware details.

The RTC is not needed for ordinary operation of the kernel and, in the 
current kernel, the EFI RTC driver is only used for IA64.  However, it 
seems to be platform independent.  I'll give it a shot (on x86, since 
that's the only architecture for which I know how to get UEFI firmware).

Paolo

[RFC v2] ARM VM System Specification

[Arnd Bergmann]

On Wednesday 11 June 2014 10:16:03 Paolo Bonzini wrote:
> 
> > If kernels actually do use the UEFI runtime services and have no need
> > for direct access to an RTC when runing in a UEFI compliant system, then
> > I agree with not specifying the hardware details.
> 
> The RTC is not needed for ordinary operation of the kernel and, in the 
> current kernel, the EFI RTC driver is only used for IA64.  However, it 
> seems to be platform independent.  I'll give it a shot (on x86, since 
> that's the only architecture for which I know how to get UEFI firmware).

Using the EFI RTC seems appropriate for ARM, as it's a reasonable
abstraction that should work with any hypervisor. I suspect the only
reason we don't use it on x86 is that we know which RTC hardware we
have and the kernel comes with a mandatory driver already.

	Arnd

[RFC v2] ARM VM System Specification

[Jon Masters]

On 6/11/14, 5:06 AM, Arnd Bergmann wrote:
> On Wednesday 11 June 2014 10:16:03 Paolo Bonzini wrote:
>>
>>> If kernels actually do use the UEFI runtime services and have no need
>>> for direct access to an RTC when runing in a UEFI compliant system, then
>>> I agree with not specifying the hardware details.
>>
>> The RTC is not needed for ordinary operation of the kernel and, in the
>> current kernel, the EFI RTC driver is only used for IA64.  However, it
>> seems to be platform independent.  I'll give it a shot (on x86, since
>> that's the only architecture for which I know how to get UEFI firmware).
>
> Using the EFI RTC seems appropriate for ARM, as it's a reasonable
> abstraction that should work with any hypervisor. I suspect the only
> reason we don't use it on x86 is that we know which RTC hardware we
> have and the kernel comes with a mandatory driver already.

(sorry for delay in responding to this thread)

Indeed. We should use the EFI RTC driver in general, rather than push 
for many individual RTC drivers on aarch64 systems that are EFI enabled. 
Within Red Hat, we currently have EFI Runtime Services live in many of 
our labs and are using the EFI RTC. This is the way forward.

Jon.

[RFC v2] ARM VM System Specification

[Christoffer Dall]

On Mon, Jun 30, 2014 at 12:19:15PM -0400, Jon Masters wrote:
> On 6/11/14, 5:06 AM, Arnd Bergmann wrote:
> >On Wednesday 11 June 2014 10:16:03 Paolo Bonzini wrote:
> >>
> >>>If kernels actually do use the UEFI runtime services and have no need
> >>>for direct access to an RTC when runing in a UEFI compliant system, then
> >>>I agree with not specifying the hardware details.
> >>
> >>The RTC is not needed for ordinary operation of the kernel and, in the
> >>current kernel, the EFI RTC driver is only used for IA64.  However, it
> >>seems to be platform independent.  I'll give it a shot (on x86, since
> >>that's the only architecture for which I know how to get UEFI firmware).
> >
> >Using the EFI RTC seems appropriate for ARM, as it's a reasonable
> >abstraction that should work with any hypervisor. I suspect the only
> >reason we don't use it on x86 is that we know which RTC hardware we
> >have and the kernel comes with a mandatory driver already.
> 
> (sorry for delay in responding to this thread)
> 
> Indeed. We should use the EFI RTC driver in general, rather than
> push for many individual RTC drivers on aarch64 systems that are EFI
> enabled. Within Red Hat, we currently have EFI Runtime Services live
> in many of our labs and are using the EFI RTC. This is the way
> forward.
> 
Seems like we should stick a note in there about being UEFI compatible
requires an RTC.  We went this far before Peter raised the issue with
noone else realizing it, so it seems like a good idea to me.

-Christoffer

[RFC v2] ARM VM System Specification

[Peter Maydell]

On 30 June 2014 21:46, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> Seems like we should stick a note in there about being UEFI compatible
> requires an RTC.  We went this far before Peter raised the issue with
> noone else realizing it, so it seems like a good idea to me.

How about:
=====
Guest OSes in the VM image should rely on the UEFI RTC API for
real time clock services. (To provide that API, the VM system will
likely need to implement some real time clock device, but the
details of these are a private implementation issue between it
and its associated UEFI implementation.)
=====

?

thanks
-- PMM

[RFC v2] ARM VM System Specification

[Stefano Stabellini]

On Mon, 30 Jun 2014, Peter Maydell wrote:
> On 30 June 2014 21:46, Christoffer Dall <christoffer.dall@linaro.org> wrote:
> > Seems like we should stick a note in there about being UEFI compatible
> > requires an RTC.  We went this far before Peter raised the issue with
> > noone else realizing it, so it seems like a good idea to me.
> 
> How about:
> =====
> Guest OSes in the VM image should rely on the UEFI RTC API for
> real time clock services. (To provide that API, the VM system will
> likely need to implement some real time clock device, but the
> details of these are a private implementation issue between it
> and its associated UEFI implementation.)

I don't see why we need to add the text within brackets: it is out of
scope for this document.

[RFC v2] ARM VM System Specification

[Peter Maydell]

On 1 July 2014 18:03, Stefano Stabellini
<stefano.stabellini@eu.citrix.com> wrote:
> On Mon, 30 Jun 2014, Peter Maydell wrote:
>> How about:
>> =====
>> Guest OSes in the VM image should rely on the UEFI RTC API for
>> real time clock services. (To provide that API, the VM system will
>> likely need to implement some real time clock device, but the
>> details of these are a private implementation issue between it
>> and its associated UEFI implementation.)
>
> I don't see why we need to add the text within brackets: it is out of
> scope for this document.

The intention is to be an informative note, not normative text
(I'm happy if we want to format the text to make that clearer,
with some sort of NOTE: markup). I'd like VM implementors
reading this spec to make the correct decisions even if they
don't happen to know inside-out the details of the UEFI
specification and what exactly UEFI demands of the hardware,
and I think it's worth adding the occasional clarifying sentence
even if it doesn't strictly speaking add any extra rules to the
specification.

thanks
-- PMM

[RFC v2] ARM VM System Specification

[Christoffer Dall]

On Tue, Jul 01, 2014 at 06:10:19PM +0100, Peter Maydell wrote:
> On 1 July 2014 18:03, Stefano Stabellini
> <stefano.stabellini@eu.citrix.com> wrote:
> > On Mon, 30 Jun 2014, Peter Maydell wrote:
> >> How about:
> >> =====
> >> Guest OSes in the VM image should rely on the UEFI RTC API for
> >> real time clock services. (To provide that API, the VM system will
> >> likely need to implement some real time clock device, but the
> >> details of these are a private implementation issue between it
> >> and its associated UEFI implementation.)
> >
> > I don't see why we need to add the text within brackets: it is out of
> > scope for this document.
> 
> The intention is to be an informative note, not normative text
> (I'm happy if we want to format the text to make that clearer,
> with some sort of NOTE: markup). I'd like VM implementors
> reading this spec to make the correct decisions even if they
> don't happen to know inside-out the details of the UEFI
> specification and what exactly UEFI demands of the hardware,
> and I think it's worth adding the occasional clarifying sentence
> even if it doesn't strictly speaking add any extra rules to the
> specification.
> 
That's also the approach we've taken so far elsewhere in the document,
so I think it's useful.

-Christoffer

[RFC v2] ARM VM System Specification

[Grant Likely]

On Tue, Jun 10, 2014 at 7:56 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 10/06/2014 20:08, Peter Maydell ha scritto:
>
>> On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
>>>
>>> On 06/10/2014 10:42 AM, Peter Maydell wrote:
>>>>
>>>> I just noticed that this doesn't mandate that the platform
>>>> provides an RTC. As I understand it, the UEFI spec mandates
>>>> that there's an RTC (could somebody more familiar with UEFI
>>>> than me confirm/deny that?) so we should probably put one here.
>>>
>>>
>>> Pardon my ignorance, but what exactly disqualifies Generic Timer
>>> implementations from being used as Real Time Clocks?
>>
>>
>> So my naive view was that an RTC actually had to have
>> support for dealing with real (wall) clock time, ie
>> knowing it's 2014 and not 1970. The generic timers are
>> just timers. Or am I wrong and UEFI doesn't really
>> require that?
>
>
> The real-time clock provides four UEFI runtime services (GetTime, SetTime,
> GetWakeupTime, SetWakeupTime).  The spec says that you can return
> EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be
> retrieved/set due to a hardware error", but I don't think this is enough to
> make these two optional.  By comparison, GetWakeupTime/SetWakeupTime can
> also return EFI_UNSUPPORTED.

In practical terms, yes the VM needs to provide an RTC interface, but
I don't think it needs to appear in this spec, even if the kernel
accesses it directly. Portable images should use the UEFI service.

g.

[RFC v2] ARM VM System Specification

[Arnd Bergmann]

On Wednesday 11 June 2014 12:33:30 Grant Likely wrote:
> On Tue, Jun 10, 2014 at 7:56 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> > Il 10/06/2014 20:08, Peter Maydell ha scritto:
> >
> >> On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
> >>>
> >>> On 06/10/2014 10:42 AM, Peter Maydell wrote:
> >>>>
> >>>> I just noticed that this doesn't mandate that the platform
> >>>> provides an RTC. As I understand it, the UEFI spec mandates
> >>>> that there's an RTC (could somebody more familiar with UEFI
> >>>> than me confirm/deny that?) so we should probably put one here.
> >>>
> >>>
> >>> Pardon my ignorance, but what exactly disqualifies Generic Timer
> >>> implementations from being used as Real Time Clocks?
> >>
> >>
> >> So my naive view was that an RTC actually had to have
> >> support for dealing with real (wall) clock time, ie
> >> knowing it's 2014 and not 1970. The generic timers are
> >> just timers. Or am I wrong and UEFI doesn't really
> >> require that?
> >
> >
> > The real-time clock provides four UEFI runtime services (GetTime, SetTime,
> > GetWakeupTime, SetWakeupTime).  The spec says that you can return
> > EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be
> > retrieved/set due to a hardware error", but I don't think this is enough to
> > make these two optional.  By comparison, GetWakeupTime/SetWakeupTime can
> > also return EFI_UNSUPPORTED.
> 
> In practical terms, yes the VM needs to provide an RTC interface, but
> I don't think it needs to appear in this spec, even if the kernel
> accesses it directly. Portable images should use the UEFI service.

It sounds like it should be in the spec then, if we want people building
portable images to include the efi-rtc driver.

	Arnd

[RFC v2] ARM VM System Specification

[Grant Likely]

On Wed, Jun 11, 2014 at 12:58 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Wednesday 11 June 2014 12:33:30 Grant Likely wrote:
>> On Tue, Jun 10, 2014 at 7:56 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> > Il 10/06/2014 20:08, Peter Maydell ha scritto:
>> >
>> >> On 10 June 2014 18:04, Christopher Covington <cov@codeaurora.org> wrote:
>> >>>
>> >>> On 06/10/2014 10:42 AM, Peter Maydell wrote:
>> >>>>
>> >>>> I just noticed that this doesn't mandate that the platform
>> >>>> provides an RTC. As I understand it, the UEFI spec mandates
>> >>>> that there's an RTC (could somebody more familiar with UEFI
>> >>>> than me confirm/deny that?) so we should probably put one here.
>> >>>
>> >>>
>> >>> Pardon my ignorance, but what exactly disqualifies Generic Timer
>> >>> implementations from being used as Real Time Clocks?
>> >>
>> >>
>> >> So my naive view was that an RTC actually had to have
>> >> support for dealing with real (wall) clock time, ie
>> >> knowing it's 2014 and not 1970. The generic timers are
>> >> just timers. Or am I wrong and UEFI doesn't really
>> >> require that?
>> >
>> >
>> > The real-time clock provides four UEFI runtime services (GetTime, SetTime,
>> > GetWakeupTime, SetWakeupTime).  The spec says that you can return
>> > EFI_DEVICE_ERROR from GetTime/SetTime if "the time could not be
>> > retrieved/set due to a hardware error", but I don't think this is enough to
>> > make these two optional.  By comparison, GetWakeupTime/SetWakeupTime can
>> > also return EFI_UNSUPPORTED.
>>
>> In practical terms, yes the VM needs to provide an RTC interface, but
>> I don't think it needs to appear in this spec, even if the kernel
>> accesses it directly. Portable images should use the UEFI service.
>
> It sounds like it should be in the spec then, if we want people building
> portable images to include the efi-rtc driver.

Fair enough.

g.

[RFC v2] ARM VM System Specification

[Peter Maydell]

On 11 June 2014 12:33, Grant Likely <grant.likely@linaro.org> wrote:
> In practical terms, yes the VM needs to provide an RTC interface, but
> I don't think it needs to appear in this spec, even if the kernel
> accesses it directly. Portable images should use the UEFI service.

I think it might helpful to include some implementation notes
to the effect that the VM needs to provide certain things to
the associated UEFI implementation but that these aren't
part of the specification and the guest OS is expected to
use the UEFI interfaces, just for the sake of clarity for people
who aren't too familiar with what UEFI requires or provides.

thanks
-- PMM

[RFC v2] ARM VM System Specification

[Claudio Fontana]

Hello all,

I just wanted to share with you guys how we are using virtualization on ARM64 over here for the OSv project.
I don't know if that's something that could be useful for your specification effort.

In OSv, creating and starting a VM to some level means starting an application.
That is, OSv should be a very thin bare bones guest server OS, which also acts as a kind of run-time library for an application to run.
All the devices are assumed to be virtualized and heavily relying on virtio.

Therefore we see a higher need for quick VM launch than it might be for other use cases.

One aspect of this is that we currently start executing the image directly (no UEFI involved on the guest),
and in some cases we might not need a full fledged file system at all,
as the communication can happen via virtio channels.

We do have a need for ACPI for discovery of information like gic addresses, timers, interrupts... (no interest on device trees, really), and of PCI-E.

By skipping steps like UEFI, grub, firmware load, etc we strive to keep our application launch time low.
Is this going to create problems for us in the future if you start requiring every VM to boot using those instead?

Thank you for your comments,

Claudio


On 28.03.2014 19:45, Christoffer Dall wrote:
> ARM VM System Specification
> ===========================
> 
> Goal
> ----
> The goal of this spec is to allow suitably-built OS images to run on
> all ARM virtualization solutions, such as KVM or Xen.
> 
> Recommendations in this spec are valid for aarch32 and aarch64 alike, and
> they aim to be hypervisor agnostic.
> 
> Note that simply adhering to the SBSA [2] is not a valid approach, for
> example because the SBSA mandates EL2, which will not be available for
> VMs.  Further, this spec also covers the aarch32 execution mode, not
> covered in the SBSA.
> 
> 
> Image format
> ------------
> The image format, as presented to the VM, needs to be well-defined in
> order for prepared disk images to be bootable across various
> virtualization implementations.
> 
> The raw disk format as presented to the VM must be partitioned with a
> GUID Partition Table (GPT).  The bootable software must be placed in the
> EFI System Partition (ESP), using the UEFI removable media path, and
> must be an EFI application complying to the UEFI Specification 2.4
> Revision A [6].
> 
> The ESP partition's GPT entry's partition type GUID must be
> C12A7328-F81F-11D2-BA4B-00A0C93EC93B and the file system must be
> formatted as FAT32/vfat as per Section 12.3.1.1 in [6].
> 
> The removable media path is \EFI\BOOT\BOOTARM.EFI for the aarch32
> execution state and is \EFI\BOOT\BOOTAA64.EFI for the aarch64 execution
> state as specified in Section 3.3 (3.3 (Boot Option Variables Default Boot
> Behavior) and 3.4.1.1 (Removable Media Boot Behavior) in [6].
> 
> This ensures that tools for both Xen and KVM can load a binary UEFI
> firmware which can read and boot the EFI application in the disk image.
> 
> A typical scenario will be GRUB2 packaged as an EFI application, which
> mounts the system boot partition and boots Linux.
> 
> 
> Virtual Firmware
> ----------------
> The VM system must be UEFI compliant in order to be able to boot the EFI
> application in the ESP.  It is recommended that this is achieved by
> loading a UEFI binary as the first software executed by the VM, which
> then executes the EFI application.  The UEFI implementation should be
> compliant with UEFI Specification 2.4 Revision A [6] or later.
> 
> This document strongly recommends that the VM implementation supports
> persistent environment storage for virtual firmware implementation in
> order to ensure probable use cases such as adding additional disk images
> to a VM or running installers to perform upgrades.
> 
> This document strongly recommends that VM implementations implement
> persistent variable storage for their UEFI implementation.  Persistent
> variable storage shall be a property of a VM instance, but shall not be
> stored as part of a portable disk image.  Portable disk images shall
> conform to the UEFI removable disk requirements from the UEFI spec and
> cannot rely on on a pre-configured UEFI environment.
> 
> The binary UEFI firmware implementation should not be distributed as
> part of the VM image, but is specific to the VM implementation.
> 
> 
> Hardware Description
> --------------------
> The VM system must be UEFI compliant and therefore the UEFI system table
> will provide a means to access hardware description data.
> 
> The VM implementation must provide through its UEFI implementation:
> 
>   a complete FDT which describes the entire VM system and will boot
>   mainline kernels driven by device tree alone
> 
> For more information about the arm and arm64 boot conventions, see
> Documentation/arm/Booting and Documentation/arm64/booting.txt in the
> Linux kernel source tree.
> 
> For more information about UEFI booting, see [4] and [5].
> 
> 
> VM Platform
> -----------
> The specification does not mandate any specific memory map.  The guest
> OS must be able to enumerate all processing elements, devices, and
> memory through HW description data (FDT) or a bus-specific
> mechanism such as PCI.
> 
> If aarch64 physical CPUs implement support for the aarch32 execution
> state in EL1 and EL0 execution, it is recommended that the VM
> implementation supports booting the VM at EL1 in both aarch32 and
> aarch64 execution states.
> 
> The virtual hardware platform must provide a number of mandatory
> peripherals:
> 
>   Serial console:  The platform should provide a console,
>   based on an emulated pl011, a virtio-console, or a Xen PV console.
> 
>   An ARM Generic Interrupt Controller v2 (GICv2) [3] or newer.  GICv2
>   limits the the number of virtual CPUs to 8 cores, newer GIC versions
>   removes this limitation.
> 
>   The ARM virtual timer and counter should be available to the VM as
>   per the ARM Generic Timers specification in the ARM ARM [1].
> 
> It is strongly recommended that the VM implementation provides a
> hotpluggable bus to support hotplug of at least block and network
> devices.  Suitable buses include a virtual PCIe bus and the Xen PV bus.
> 
> For the VM image to be compliant with this spec, the following applies
> for the guest OS in the VM image:
> 
>   The guest OS must include support for pl011 UART, virtio-console, and
>   the Xen PV console.
> 
>   The guest OS must include support for GICv2 and any available newer
>   version of the GIC architecture to maintain compatibility with older
>   VM implementations.
> 
>   It is strongly recommended to include support for all available
>   (block, network, console, balloon) virtio-pci, virtio-mmio, and Xen PV
>   drivers in the guest OS kernel or initial ramdisk.
> 
> 
> Other common peripherals for block devices, networking, and more can
> (and typically will) be provided, but OS software written and compiled
> to run on ARM VMs cannot make any assumptions about which variations
> of these should exist or which implementation they use (e.g. VirtIO or
> Xen PV).  See "Hardware Description" above.
> 
> 
> Changes from previous versions of this RFC
> ------------------------------------------
> Changes v1-v2:
>  - Clearly specify that the guest must support the pl011,
>    virtio-console, and Xen PV console.  (Note that it was discussed to
>    mandate a pl011 during Linaro Connect Asia 2014, but that was under the
>    impression that the SBSA specification was an output-only no-irq
>    serial port, which is not the case.  The only two benefits from
>    mandating a specific serial type was to handle "console=ttyAMA0"
>    kernel command line parameters and earlyprintk; Grant Likely has
>    submitted patches to avoid the need for "console=" parameters, and
>    Rob Herring has submitted patches for paravirtualized earlyprintk
>    consoles.)
>  - Reference EFI specification for bootable paths.
>  - Remove discussion on ACPI boot methods and do not suggest ACPI
>    support in VMs.
>  - Add specification about UEFI persistent variable storage and
>    portability.
> 
> 
> References
> ----------
> [1]: The ARM Architecture Reference Manual, ARMv8, Issue A.b
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html
> 
> [2]: ARM Server Base System Architecture
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0029/index.html
> 
> [3]: The ARM Generic Interrupt Controller Architecture Specifications v2.0
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html
> 
> [4]: http://www.secretlab.ca/archives/27
> 
> [5]: https://git.linaro.org/people/leif.lindholm/linux.git/blob/refs/heads/uefi-for-upstream:/Documentation/arm/uefi.txt
> 
> [6]: UEFI Specification 2.4 Revision A
> http://www.uefi.org/sites/default/files/resources/2_4_Errata_A.pdf
> _______________________________________________
> kvmarm mailing list
> kvmarm at lists.cs.columbia.edu
> https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> 


-- 
Claudio Fontana
Server Virtualization Architect
Huawei Technologies Duesseldorf GmbH
Riesstra?e 25 - 80992 M?nchen

office: +49 89 158834 4135
mobile: +49 15253060158

[RFC v2] ARM VM System Specification

[Arnd Bergmann]

On Tuesday 10 June 2014 18:44:59 Claudio Fontana wrote:
> I just wanted to share with you guys how we are using virtualization
> on ARM64 over here for the OSv project.
> By skipping steps like UEFI, grub, firmware load, etc we strive to
> keep our application launch time low.
> Is this going to create problems for us in the future if you start
> requiring every VM to boot using those instead?

My feeling is that it's out of scope for this specification.
What you are doing is great, and you should keep doing it that way.

It does mean that your applications are aware of which hypervisor
they are running on, and you have to manage them using OSv specific
tools on the host.

The VM System Specification however is meant to provide a way to
distribute a file system image for a virtual machine that can run
on any compliant hypervisor using any compliant management tools.
The reason it goes through all the boot loader steps is to make it
much closer to a real system, so distros don't have to special-case
this.

If you don't care about that, you can just install the tools on
the host to manage your OSv application without a boot loader.
In particular, you can support multiple targets on OSv: e.g.
native Xen, native KVM, and portable standard hypervisor following
the ARM VM System Spec.

	Arnd

[RFC v2] ARM VM System Specification

[Stefano Stabellini]

Although not in the ARM VM System Specification, Xen is certainly going
to support a fast boot path without UEFI firmware. I guess KVM will too.
You'll have to rely on hypervisor specific mechanisms to achieve it.

In fact I wouldn't worry about UEFI when you need ACPI, that is not in
this specification. Moreover the only hypervisor supporting virtio on
ARM is KVM as far as I know.

So it looks like you are already tying yourself to one hypervisor (KVM)
and an out-of-spec standard (ACPI). The ARM VM System Specification is
for people that intend to produce cross-hypervisor images.


On Tue, 10 Jun 2014, Claudio Fontana wrote:
> Hello all,
> 
> I just wanted to share with you guys how we are using virtualization on ARM64 over here for the OSv project.
> I don't know if that's something that could be useful for your specification effort.
> 
> In OSv, creating and starting a VM to some level means starting an application.
> That is, OSv should be a very thin bare bones guest server OS, which also acts as a kind of run-time library for an application to run.
> All the devices are assumed to be virtualized and heavily relying on virtio.
> 
> Therefore we see a higher need for quick VM launch than it might be for other use cases.
> 
> One aspect of this is that we currently start executing the image directly (no UEFI involved on the guest),
> and in some cases we might not need a full fledged file system at all,
> as the communication can happen via virtio channels.
> 
> We do have a need for ACPI for discovery of information like gic addresses, timers, interrupts... (no interest on device trees, really), and of PCI-E.
> 
> By skipping steps like UEFI, grub, firmware load, etc we strive to keep our application launch time low.
> Is this going to create problems for us in the future if you start requiring every VM to boot using those instead?
> 
> Thank you for your comments,
> 
> Claudio
> 
> 
> On 28.03.2014 19:45, Christoffer Dall wrote:
> > ARM VM System Specification
> > ===========================
> > 
> > Goal
> > ----
> > The goal of this spec is to allow suitably-built OS images to run on
> > all ARM virtualization solutions, such as KVM or Xen.
> > 
> > Recommendations in this spec are valid for aarch32 and aarch64 alike, and
> > they aim to be hypervisor agnostic.
> > 
> > Note that simply adhering to the SBSA [2] is not a valid approach, for
> > example because the SBSA mandates EL2, which will not be available for
> > VMs.  Further, this spec also covers the aarch32 execution mode, not
> > covered in the SBSA.
> > 
> > 
> > Image format
> > ------------
> > The image format, as presented to the VM, needs to be well-defined in
> > order for prepared disk images to be bootable across various
> > virtualization implementations.
> > 
> > The raw disk format as presented to the VM must be partitioned with a
> > GUID Partition Table (GPT).  The bootable software must be placed in the
> > EFI System Partition (ESP), using the UEFI removable media path, and
> > must be an EFI application complying to the UEFI Specification 2.4
> > Revision A [6].
> > 
> > The ESP partition's GPT entry's partition type GUID must be
> > C12A7328-F81F-11D2-BA4B-00A0C93EC93B and the file system must be
> > formatted as FAT32/vfat as per Section 12.3.1.1 in [6].
> > 
> > The removable media path is \EFI\BOOT\BOOTARM.EFI for the aarch32
> > execution state and is \EFI\BOOT\BOOTAA64.EFI for the aarch64 execution
> > state as specified in Section 3.3 (3.3 (Boot Option Variables Default Boot
> > Behavior) and 3.4.1.1 (Removable Media Boot Behavior) in [6].
> > 
> > This ensures that tools for both Xen and KVM can load a binary UEFI
> > firmware which can read and boot the EFI application in the disk image.
> > 
> > A typical scenario will be GRUB2 packaged as an EFI application, which
> > mounts the system boot partition and boots Linux.
> > 
> > 
> > Virtual Firmware
> > ----------------
> > The VM system must be UEFI compliant in order to be able to boot the EFI
> > application in the ESP.  It is recommended that this is achieved by
> > loading a UEFI binary as the first software executed by the VM, which
> > then executes the EFI application.  The UEFI implementation should be
> > compliant with UEFI Specification 2.4 Revision A [6] or later.
> > 
> > This document strongly recommends that the VM implementation supports
> > persistent environment storage for virtual firmware implementation in
> > order to ensure probable use cases such as adding additional disk images
> > to a VM or running installers to perform upgrades.
> > 
> > This document strongly recommends that VM implementations implement
> > persistent variable storage for their UEFI implementation.  Persistent
> > variable storage shall be a property of a VM instance, but shall not be
> > stored as part of a portable disk image.  Portable disk images shall
> > conform to the UEFI removable disk requirements from the UEFI spec and
> > cannot rely on on a pre-configured UEFI environment.
> > 
> > The binary UEFI firmware implementation should not be distributed as
> > part of the VM image, but is specific to the VM implementation.
> > 
> > 
> > Hardware Description
> > --------------------
> > The VM system must be UEFI compliant and therefore the UEFI system table
> > will provide a means to access hardware description data.
> > 
> > The VM implementation must provide through its UEFI implementation:
> > 
> >   a complete FDT which describes the entire VM system and will boot
> >   mainline kernels driven by device tree alone
> > 
> > For more information about the arm and arm64 boot conventions, see
> > Documentation/arm/Booting and Documentation/arm64/booting.txt in the
> > Linux kernel source tree.
> > 
> > For more information about UEFI booting, see [4] and [5].
> > 
> > 
> > VM Platform
> > -----------
> > The specification does not mandate any specific memory map.  The guest
> > OS must be able to enumerate all processing elements, devices, and
> > memory through HW description data (FDT) or a bus-specific
> > mechanism such as PCI.
> > 
> > If aarch64 physical CPUs implement support for the aarch32 execution
> > state in EL1 and EL0 execution, it is recommended that the VM
> > implementation supports booting the VM at EL1 in both aarch32 and
> > aarch64 execution states.
> > 
> > The virtual hardware platform must provide a number of mandatory
> > peripherals:
> > 
> >   Serial console:  The platform should provide a console,
> >   based on an emulated pl011, a virtio-console, or a Xen PV console.
> > 
> >   An ARM Generic Interrupt Controller v2 (GICv2) [3] or newer.  GICv2
> >   limits the the number of virtual CPUs to 8 cores, newer GIC versions
> >   removes this limitation.
> > 
> >   The ARM virtual timer and counter should be available to the VM as
> >   per the ARM Generic Timers specification in the ARM ARM [1].
> > 
> > It is strongly recommended that the VM implementation provides a
> > hotpluggable bus to support hotplug of at least block and network
> > devices.  Suitable buses include a virtual PCIe bus and the Xen PV bus.
> > 
> > For the VM image to be compliant with this spec, the following applies
> > for the guest OS in the VM image:
> > 
> >   The guest OS must include support for pl011 UART, virtio-console, and
> >   the Xen PV console.
> > 
> >   The guest OS must include support for GICv2 and any available newer
> >   version of the GIC architecture to maintain compatibility with older
> >   VM implementations.
> > 
> >   It is strongly recommended to include support for all available
> >   (block, network, console, balloon) virtio-pci, virtio-mmio, and Xen PV
> >   drivers in the guest OS kernel or initial ramdisk.
> > 
> > 
> > Other common peripherals for block devices, networking, and more can
> > (and typically will) be provided, but OS software written and compiled
> > to run on ARM VMs cannot make any assumptions about which variations
> > of these should exist or which implementation they use (e.g. VirtIO or
> > Xen PV).  See "Hardware Description" above.
> > 
> > 
> > Changes from previous versions of this RFC
> > ------------------------------------------
> > Changes v1-v2:
> >  - Clearly specify that the guest must support the pl011,
> >    virtio-console, and Xen PV console.  (Note that it was discussed to
> >    mandate a pl011 during Linaro Connect Asia 2014, but that was under the
> >    impression that the SBSA specification was an output-only no-irq
> >    serial port, which is not the case.  The only two benefits from
> >    mandating a specific serial type was to handle "console=ttyAMA0"
> >    kernel command line parameters and earlyprintk; Grant Likely has
> >    submitted patches to avoid the need for "console=" parameters, and
> >    Rob Herring has submitted patches for paravirtualized earlyprintk
> >    consoles.)
> >  - Reference EFI specification for bootable paths.
> >  - Remove discussion on ACPI boot methods and do not suggest ACPI
> >    support in VMs.
> >  - Add specification about UEFI persistent variable storage and
> >    portability.
> > 
> > 
> > References
> > ----------
> > [1]: The ARM Architecture Reference Manual, ARMv8, Issue A.b
> > http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html
> > 
> > [2]: ARM Server Base System Architecture
> > http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0029/index.html
> > 
> > [3]: The ARM Generic Interrupt Controller Architecture Specifications v2.0
> > http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html
> > 
> > [4]: http://www.secretlab.ca/archives/27
> > 
> > [5]: https://git.linaro.org/people/leif.lindholm/linux.git/blob/refs/heads/uefi-for-upstream:/Documentation/arm/uefi.txt
> > 
> > [6]: UEFI Specification 2.4 Revision A
> > http://www.uefi.org/sites/default/files/resources/2_4_Errata_A.pdf
> > _______________________________________________
> > kvmarm mailing list
> > kvmarm at lists.cs.columbia.edu
> > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> > 
> 
> 
> -- 
> Claudio Fontana
> Server Virtualization Architect
> Huawei Technologies Duesseldorf GmbH
> Riesstra?e 25 - 80992 M?nchen
> 
> office: +49 89 158834 4135
> mobile: +49 15253060158
> 

[RFC v2] ARM VM System Specification

[Christoffer Dall]

Agree with what Stefano says, and I strongly recommend you reconsider
your position on FDT vs. ACPI for ARM VMs, but it's completely up to
you of course :)

-Christoffer

On Wed, Jun 11, 2014 at 10:50:04AM +0100, Stefano Stabellini wrote:
> Although not in the ARM VM System Specification, Xen is certainly going
> to support a fast boot path without UEFI firmware. I guess KVM will too.
> You'll have to rely on hypervisor specific mechanisms to achieve it.
> 
> In fact I wouldn't worry about UEFI when you need ACPI, that is not in
> this specification. Moreover the only hypervisor supporting virtio on
> ARM is KVM as far as I know.
> 
> So it looks like you are already tying yourself to one hypervisor (KVM)
> and an out-of-spec standard (ACPI). The ARM VM System Specification is
> for people that intend to produce cross-hypervisor images.
> 
> 
> On Tue, 10 Jun 2014, Claudio Fontana wrote:
> > Hello all,
> > 
> > I just wanted to share with you guys how we are using virtualization on ARM64 over here for the OSv project.
> > I don't know if that's something that could be useful for your specification effort.
> > 
> > In OSv, creating and starting a VM to some level means starting an application.
> > That is, OSv should be a very thin bare bones guest server OS, which also acts as a kind of run-time library for an application to run.
> > All the devices are assumed to be virtualized and heavily relying on virtio.
> > 
> > Therefore we see a higher need for quick VM launch than it might be for other use cases.
> > 
> > One aspect of this is that we currently start executing the image directly (no UEFI involved on the guest),
> > and in some cases we might not need a full fledged file system at all,
> > as the communication can happen via virtio channels.
> > 
> > We do have a need for ACPI for discovery of information like gic addresses, timers, interrupts... (no interest on device trees, really), and of PCI-E.
> > 
> > By skipping steps like UEFI, grub, firmware load, etc we strive to keep our application launch time low.
> > Is this going to create problems for us in the future if you start requiring every VM to boot using those instead?
> > 
> > Thank you for your comments,
> > 
> > Claudio
> > 
> > 
> > On 28.03.2014 19:45, Christoffer Dall wrote:
> > > ARM VM System Specification
> > > ===========================
> > > 
> > > Goal
> > > ----
> > > The goal of this spec is to allow suitably-built OS images to run on
> > > all ARM virtualization solutions, such as KVM or Xen.
> > > 
> > > Recommendations in this spec are valid for aarch32 and aarch64 alike, and
> > > they aim to be hypervisor agnostic.
> > > 
> > > Note that simply adhering to the SBSA [2] is not a valid approach, for
> > > example because the SBSA mandates EL2, which will not be available for
> > > VMs.  Further, this spec also covers the aarch32 execution mode, not
> > > covered in the SBSA.
> > > 
> > > 
> > > Image format
> > > ------------
> > > The image format, as presented to the VM, needs to be well-defined in
> > > order for prepared disk images to be bootable across various
> > > virtualization implementations.
> > > 
> > > The raw disk format as presented to the VM must be partitioned with a
> > > GUID Partition Table (GPT).  The bootable software must be placed in the
> > > EFI System Partition (ESP), using the UEFI removable media path, and
> > > must be an EFI application complying to the UEFI Specification 2.4
> > > Revision A [6].
> > > 
> > > The ESP partition's GPT entry's partition type GUID must be
> > > C12A7328-F81F-11D2-BA4B-00A0C93EC93B and the file system must be
> > > formatted as FAT32/vfat as per Section 12.3.1.1 in [6].
> > > 
> > > The removable media path is \EFI\BOOT\BOOTARM.EFI for the aarch32
> > > execution state and is \EFI\BOOT\BOOTAA64.EFI for the aarch64 execution
> > > state as specified in Section 3.3 (3.3 (Boot Option Variables Default Boot
> > > Behavior) and 3.4.1.1 (Removable Media Boot Behavior) in [6].
> > > 
> > > This ensures that tools for both Xen and KVM can load a binary UEFI
> > > firmware which can read and boot the EFI application in the disk image.
> > > 
> > > A typical scenario will be GRUB2 packaged as an EFI application, which
> > > mounts the system boot partition and boots Linux.
> > > 
> > > 
> > > Virtual Firmware
> > > ----------------
> > > The VM system must be UEFI compliant in order to be able to boot the EFI
> > > application in the ESP.  It is recommended that this is achieved by
> > > loading a UEFI binary as the first software executed by the VM, which
> > > then executes the EFI application.  The UEFI implementation should be
> > > compliant with UEFI Specification 2.4 Revision A [6] or later.
> > > 
> > > This document strongly recommends that the VM implementation supports
> > > persistent environment storage for virtual firmware implementation in
> > > order to ensure probable use cases such as adding additional disk images
> > > to a VM or running installers to perform upgrades.
> > > 
> > > This document strongly recommends that VM implementations implement
> > > persistent variable storage for their UEFI implementation.  Persistent
> > > variable storage shall be a property of a VM instance, but shall not be
> > > stored as part of a portable disk image.  Portable disk images shall
> > > conform to the UEFI removable disk requirements from the UEFI spec and
> > > cannot rely on on a pre-configured UEFI environment.
> > > 
> > > The binary UEFI firmware implementation should not be distributed as
> > > part of the VM image, but is specific to the VM implementation.
> > > 
> > > 
> > > Hardware Description
> > > --------------------
> > > The VM system must be UEFI compliant and therefore the UEFI system table
> > > will provide a means to access hardware description data.
> > > 
> > > The VM implementation must provide through its UEFI implementation:
> > > 
> > >   a complete FDT which describes the entire VM system and will boot
> > >   mainline kernels driven by device tree alone
> > > 
> > > For more information about the arm and arm64 boot conventions, see
> > > Documentation/arm/Booting and Documentation/arm64/booting.txt in the
> > > Linux kernel source tree.
> > > 
> > > For more information about UEFI booting, see [4] and [5].
> > > 
> > > 
> > > VM Platform
> > > -----------
> > > The specification does not mandate any specific memory map.  The guest
> > > OS must be able to enumerate all processing elements, devices, and
> > > memory through HW description data (FDT) or a bus-specific
> > > mechanism such as PCI.
> > > 
> > > If aarch64 physical CPUs implement support for the aarch32 execution
> > > state in EL1 and EL0 execution, it is recommended that the VM
> > > implementation supports booting the VM at EL1 in both aarch32 and
> > > aarch64 execution states.
> > > 
> > > The virtual hardware platform must provide a number of mandatory
> > > peripherals:
> > > 
> > >   Serial console:  The platform should provide a console,
> > >   based on an emulated pl011, a virtio-console, or a Xen PV console.
> > > 
> > >   An ARM Generic Interrupt Controller v2 (GICv2) [3] or newer.  GICv2
> > >   limits the the number of virtual CPUs to 8 cores, newer GIC versions
> > >   removes this limitation.
> > > 
> > >   The ARM virtual timer and counter should be available to the VM as
> > >   per the ARM Generic Timers specification in the ARM ARM [1].
> > > 
> > > It is strongly recommended that the VM implementation provides a
> > > hotpluggable bus to support hotplug of at least block and network
> > > devices.  Suitable buses include a virtual PCIe bus and the Xen PV bus.
> > > 
> > > For the VM image to be compliant with this spec, the following applies
> > > for the guest OS in the VM image:
> > > 
> > >   The guest OS must include support for pl011 UART, virtio-console, and
> > >   the Xen PV console.
> > > 
> > >   The guest OS must include support for GICv2 and any available newer
> > >   version of the GIC architecture to maintain compatibility with older
> > >   VM implementations.
> > > 
> > >   It is strongly recommended to include support for all available
> > >   (block, network, console, balloon) virtio-pci, virtio-mmio, and Xen PV
> > >   drivers in the guest OS kernel or initial ramdisk.
> > > 
> > > 
> > > Other common peripherals for block devices, networking, and more can
> > > (and typically will) be provided, but OS software written and compiled
> > > to run on ARM VMs cannot make any assumptions about which variations
> > > of these should exist or which implementation they use (e.g. VirtIO or
> > > Xen PV).  See "Hardware Description" above.
> > > 
> > > 
> > > Changes from previous versions of this RFC
> > > ------------------------------------------
> > > Changes v1-v2:
> > >  - Clearly specify that the guest must support the pl011,
> > >    virtio-console, and Xen PV console.  (Note that it was discussed to
> > >    mandate a pl011 during Linaro Connect Asia 2014, but that was under the
> > >    impression that the SBSA specification was an output-only no-irq
> > >    serial port, which is not the case.  The only two benefits from
> > >    mandating a specific serial type was to handle "console=ttyAMA0"
> > >    kernel command line parameters and earlyprintk; Grant Likely has
> > >    submitted patches to avoid the need for "console=" parameters, and
> > >    Rob Herring has submitted patches for paravirtualized earlyprintk
> > >    consoles.)
> > >  - Reference EFI specification for bootable paths.
> > >  - Remove discussion on ACPI boot methods and do not suggest ACPI
> > >    support in VMs.
> > >  - Add specification about UEFI persistent variable storage and
> > >    portability.
> > > 
> > > 
> > > References
> > > ----------
> > > [1]: The ARM Architecture Reference Manual, ARMv8, Issue A.b
> > > http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html
> > > 
> > > [2]: ARM Server Base System Architecture
> > > http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0029/index.html
> > > 
> > > [3]: The ARM Generic Interrupt Controller Architecture Specifications v2.0
> > > http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0487a.b/index.html
> > > 
> > > [4]: http://www.secretlab.ca/archives/27
> > > 
> > > [5]: https://git.linaro.org/people/leif.lindholm/linux.git/blob/refs/heads/uefi-for-upstream:/Documentation/arm/uefi.txt
> > > 
> > > [6]: UEFI Specification 2.4 Revision A
> > > http://www.uefi.org/sites/default/files/resources/2_4_Errata_A.pdf
> > > _______________________________________________
> > > kvmarm mailing list
> > > kvmarm at lists.cs.columbia.edu
> > > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
> > > 
> > 
> > 
> > -- 
> > Claudio Fontana
> > Server Virtualization Architect
> > Huawei Technologies Duesseldorf GmbH
> > Riesstra?e 25 - 80992 M?nchen
> > 
> > office: +49 89 158834 4135
> > mobile: +49 15253060158
> > 

[RFC v2] ARM VM System Specification

[Grant Likely]

On Wed, Jun 11, 2014 at 10:55 AM, Christoffer Dall
<christoffer.dall@linaro.org> wrote:
> Agree with what Stefano says, and I strongly recommend you reconsider
> your position on FDT vs. ACPI for ARM VMs, but it's completely up to
> you of course :)

Not entirely. The plan right now is to only support ACPI when booting
with UEFI. If they don't use UEFI, then ACPI will not be available. If
OSv only supports ACPI, then it is forced to use the UEFI boot path.

g.

[RFC v2] ARM VM System Specification

[Christoffer Dall]

On Wed, Jun 11, 2014 at 12:28:40PM +0100, Grant Likely wrote:
> On Wed, Jun 11, 2014 at 10:55 AM, Christoffer Dall
> <christoffer.dall@linaro.org> wrote:
> > Agree with what Stefano says, and I strongly recommend you reconsider
> > your position on FDT vs. ACPI for ARM VMs, but it's completely up to
> > you of course :)
> 
> Not entirely. 

of course it's up to them what they want to do.

> The plan right now is to only support ACPI when booting
> with UEFI. If they don't use UEFI, then ACPI will not be available. If
> OSv only supports ACPI, then it is forced to use the UEFI boot path.
> 
The plan right now is to not support ACPI in VMs at all, as per the last
discussion at LCA14.  If an when someone wants to add that, fine, but
the spec mandates FDT describing the full system.

If OSv wants to hack a KVM implementation or provide a static ACPI blob
coupled to OSv that happens to describe the KVM/ARM/QEMU system model,
then they can do that.  Crazy, it sounds to me, but as I said, up to the
OSv guys.

-Christoffer

[RFC v2] ARM VM System Specification

[Arnd Bergmann]

On Wednesday 11 June 2014 10:50:04 Stefano Stabellini wrote:
> Although not in the ARM VM System Specification, Xen is certainly going
> to support a fast boot path without UEFI firmware. I guess KVM will too.
> You'll have to rely on hypervisor specific mechanisms to achieve it.
> 
> In fact I wouldn't worry about UEFI when you need ACPI, that is not in
> this specification. Moreover the only hypervisor supporting virtio on
> ARM is KVM as far as I know.

Ah right, I missed the part about ACPI.

> > One aspect of this is that we currently start executing the image directly (no UEFI involved on the guest),
> > and in some cases we might not need a full fledged file system at all,
> > as the communication can happen via virtio channels.
> > 
> > We do have a need for ACPI for discovery of information like gic addresses, 
> > timers, interrupts... (no interest on device trees, really), and of PCI-E.

I wonder how you'd expect to find the ACPI data when there is no UEFI.
It's not likely that any hypervisor would ship with an ACPI implementation
that is independent of UEFI, because Linux (or any other full OS for
that matter) would support that scenario. You could of course link OSv
with an ACPI binary that is specific to KVM, but then I don't know why
you wouldn't just hardcode the data in OSv directly.

	Arnd

[RFC v2] ARM VM System Specification

[Grant Likely]

On 10 Jun 2014 17:45, "Claudio Fontana" <claudio.fontana@huawei.com> wrote:
>
> Hello all,
>
> I just wanted to share with you guys how we are using virtualization on ARM64 over here for the OSv project.
> I don't know if that's something that could be useful for your specification effort.
>
> In OSv, creating and starting a VM to some level means starting an application.
> That is, OSv should be a very thin bare bones guest server OS, which also acts as a kind of run-time library for an application to run.
> All the devices are assumed to be virtualized and heavily relying on virtio.
>
> Therefore we see a higher need for quick VM launch than it might be for other use cases.
>
> One aspect of this is that we currently start executing the image directly (no UEFI involved on the guest),
> and in some cases we might not need a full fledged file system at all,
> as the communication can happen via virtio channels.

The purpose of this spec is for creating portable disk images. It is
intended to support the virtual-machine-looks-just-like-a-real-machine
model, and is intended to provide exactly the same interface to
installers as to real machines.

It isn't really interesting for use cases like OSv or anyone who wants
to start the kernel directly. You don't need UEFI in that case because
the host has pre-knowledge of which kernel binary to load. In that
regard this spec doesn't affect you.

>
> We do have a need for ACPI for discovery of information like gic addresses, timers, interrupts... (no interest on device trees, really), and of PCI-E.

This may be a problem for you then. The only time we're planning to
support ACPI in a VM is when UEFI is used for booting. Even the first
version of this spec specifies FDT, not ACPI. FDT support is there now
in Xen and KVM, but there is nothing for ACPI on ARM VMs.

What is the objection to obtaining discovery information from FDT?

> By skipping steps like UEFI, grub, firmware load, etc we strive to keep our application launch time low.
> Is this going to create problems for us in the future if you start requiring every VM to boot using those instead?

No, we're not requiring a full firmware stack to boot. As described
above, this is only for booting disk images.

g.