Re: [PATCH] arm64: dts: Fix GIC reg sizes for APM X-Gene

On Tue, Feb 24, 2015 at 12:34 AM, Pranavkumar Sawargaonkar
[off-list ref] wrote:

Hi Rob,

On Mon, Feb 23, 2015 at 10:09 PM, Rob Herring [off-list ref] wrote:

quoted

On Mon, Feb 23, 2015 at 6:07 AM, Christoffer Dall
[off-list ref] wrote:

quoted

On Sat, Feb 21, 2015 at 03:56:17PM -0600, Rob Herring wrote:

quoted

On Thu, Feb 19, 2015 at 1:03 PM, Christoffer Dall
[off-list ref] wrote:

quoted

On Thu, Feb 19, 2015 at 12:23:15PM -0600, Rob Herring wrote:

quoted

On Tue, Jan 27, 2015 at 1:03 AM, Pranavkumar Sawargaonkar
[off-list ref] wrote:

quoted

In APM X-Gene, GIC register space is 64K aligned while the sizes mentioned
in the dt are 4K aligned. This breaks KVM when kernel is built with 64K page
size due to size alignment checking in vgic driver for VCPU Control and
VCPU register.

This patch corrects the sizes to be inline with the hardware spec.

This does not make sense. The GIC regions are still only 4 or 8KB and
the h/w description should reflect that. For implementations using
gic-400 and the addressing decode trick, the rest of the register
range is also not safe to access given it is multiple mapped. Also,
this wastes virtual space, but I guess we don't care on 64-bit.

KVM should be fixed to only check base address alignment. Size
alignment does not matter (if it does, then you need to fix all
register blocks).

It matters if you want to ensure that the 64K page you are assigning to
a guest for the GIC virtual CPU interface contains only GIC virtual CPU
mappings, and not other random stuff that the guest is not allowed to
touch.

Good point.

quoted

How else should this be enforced?

Rely on correct h/w design? You'll have to repeat this every time you
want to do pass-thru of a device.

What do you do if 64K mapping is not supported? Fallback to emulation
of the CPU interface?

Agree with Peter on these two points.

quoted

Are there other DTSs that need to be fixed?

Not sure really, AMD Seattle works with 64K pages IIRC.

Well, looks we have been inconsistent here:

arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-           reg = <0x0
0xe1110000 0 0x1000>,
arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-                 <0x0
0xe112f000 0 0x2000>,
arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-                 <0x0
0xe1140000 0 0x10000>,
arch/arm64/boot/dts/amd/amd-seattle-soc.dtsi-                 <0x0
0xe1160000 0 0x10000>;

arch/arm64/boot/dts/arm/juno.dts-               reg = <0x0 0x2c010000 0 0x1000>,
arch/arm64/boot/dts/arm/juno.dts-                     <0x0 0x2c02f000 0 0x2000>,
arch/arm64/boot/dts/arm/juno.dts-                     <0x0 0x2c04f000 0 0x2000>,
arch/arm64/boot/dts/arm/juno.dts-                     <0x0 0x2c06f000 0 0x2000>;

If we are going to use 64K sizes, can we have some consistency here
please. Which ranges really need 64KB sizes? It should only be the
VCPU interface. right? Why does XGene need 128K? If XGene is doing
address swizzling, then the CPU and VCPU base addresses are wrong.
Seattle is also wrong for the VCPU, but no one has noticed because we
don't use the DIR register IIRC.

XGene should also add an "arm,gic-400" compatible string or something
XGene specific if in fact it is not GIC-400.

X-Gene has gic-400 as an interrupt controller.
Only thing is GIC pages are mapped at 64K boundary (with 64K page size)
Hence CPU, VCPU interfaces has a size of 128K (2GIC pages)
Regarding GICC_DIR, yes there is a problem which needs to be solved
since the first page size is 64K.
In XEN we already have a small fix to access GICC_DIR with 64K page
offset instead of standard 4K.

Right, and in order for this to work, you should use the last 4K alias
for the cpu interface(s). This is why other platforms use xxxf000 as
their cpu interface base.

It is of course possible that xgene does not properly do the address
swizzling and therefore you have to use 64K aligned addresses. But in
that case you need a unique compatible string.

I remember a small discussion in this regard in past
(http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/266468.html)
which was deferred at that time.
Once this patch is accepted we can post RFC patch to address GICC_DIR
and discuss further.

No, let's get this right now and not keep changing the dts.

Rob

quoted

I think perhaps we need a specific compatible property to indicate a
GIC-400 with address swizzling. While we could get away with using the
aliased addresses, that seems to be hard to get right and we may
regret not doing it in the long term. It would indicate at least it is
64K page safe for example.

Rob

Thanks,
Pranav

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