Re: [Xen-devel] [PATCH] efi/libstub/fdt: Standardize the names of EFI stub parameters

[Leif Lindholm]

On Thu, Sep 10, 2015 at 02:52:25PM +0100, Stefano Stabellini wrote:
> > > In any case this should be separate from the shim ABI discussion.
> > 
> > I disagree; I think this is very much relevant to the ABI discussion.
> > That's not to say that I insist on a particular approach, but I think
> > that they need to be considered together.
> 
> Let's suppose Xen didn't expose any RuntimeServices at all, would that
> make it easier to discuss about the EFI stub parameters?

Possibly :)

> In the grant
> scheme of things, they are not that important, as Ian wrote what is
> important is how to pass the RSDP.

So, we have discussed in the past having the ability to get at
configuration tables when UEFI is not available. Say, for example,
that we wanted SMBIOS support on a platform with U-Boot firmware.

Since all that is needed then is a UEFI System Table with a pointer to
a configuration table array, this should be fairly straightforward to
implement statically. The other parameters would not be necessary.

It would however require minor changes to the arm64 kernel UEFI support.

/
Leif

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Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen - version 5

[Leif Lindholm]

On Wed, Sep 02, 2015 at 03:57:51PM +0200, Christoffer Dall wrote:
> On Wed, Sep 2, 2015 at 3:54 PM, Ian Campbell  wrote:
> > On Wed, 2015-09-02 at 14:48 +0100, Julien Grall wrote:
> >> On 02/09/15 14:26, Ian Campbell wrote:
> >> > > > > I think the problem is how you reserved this region in the EFI
> >> > > > > memory
> >> > > > > table. From what I saw, you marked this new memory with
> >> > > > > EFI_MEMORY_WB
> >> > > > > (which means that the region can be usable by Linux).
> >> > > > >
> >> > > > Yes, I mark it with EFI_MEMORY_WB. Is this right?
> >> > >
> >> > > I would say no, but it's only because I looked at the kernel code
> >> > > quickly.
> >> > >
> >> > > You have to looks how ACPI region/UEFI tables are described in the
> >> > > host
> >> > > EFI memory map and mimicking for the DOM0 EFI memory map.
> >> >
> >> > Surely it is the type (EfiACPIReclaimMemory, EfiACPIMemoryNVS etc) and
> >> > not
> >> > the mapping attributes which should control whether an OS considers a
> >> > region usable? At least until the OS is done parsing tables neither of
> >> > those are usable (which implies we want NVS as our type, unless the
> >> > memory
> >> > is intended to be reclaimed by dom0, implying it should own it).

The mapping attributes are checked to see whether a page _could_ be
used as generic RAM or not. is_reserve_region() determines whether it
should.

> >> It looks like that Linux on ARM64 is considering any region with
> >> EFI_MEMORY_WB set as normal RAM and will try to add as System RAM (see
> >> reserve_regions in arch/arm64/kernel/efi.c).

The current state of things ends up being basically:
if (EFI_MEMORY_WB)
   memblock_add()
if (EFI_MEMORY_WB && !reclaimable_region)
   memblock_reserve()

That is, apart from counterintuitive, a bug.
It should be using memblock_remove() instead.

> > It's hard to believe this isn't a bug... It's probably worth asking the
> > Linux maintainers about this.
> 
> wasn't this that whole workaround to make sure Linux maps the data as
> regular RAM, because otherwise architecture generic code would map it
> as IO memory,

I hope not.

> and generic routines such as memcpy would fault on
> unaligned accesses, or am I confusing ACPI with EFI here?

Even ACPI tables should need to be in Normal memory in order to work
as expected.

> Leif (added to the to-field) had some insight on this earlier on.

(Adding Ard as well.)
Ard wrote a series end of last year to clean much of this up, but it's
not been merged:
http://thread.gmane.org/gmane.linux.kernel.efi/5133

We should probably push for this to go in as a bugfix, and those
interested in seeing this can weigh in in public.

/
Leif

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