Re: [PATCH v7 00/17] Add support for Clang LTO

Marc Zyngier
2020-11-21T11:41:50Z

On 2020-11-20 23:53, Nick Desaulniers wrote:
> On Fri, Nov 20, 2020 at 3:30 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>>
>> On Fri, 20 Nov 2020 at 21:19, Nick Desaulniers
>> <ndesaulniers@google.com> wrote:
>> >
>> > On Fri, Nov 20, 2020 at 2:30 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>> > >
>> > > On Thu, 19 Nov 2020 at 00:42, Nick Desaulniers <ndesaulniers@google.com> wrote:
>> > > >
>> > > > Thanks for continuing to drive this series Sami. For the series,
>> > > >
>> > > > Tested-by: Nick Desaulniers <ndesaulniers@google.com>
>> > > >
>> > > > I did virtualized boot tests with the series applied to aarch64
>> > > > defconfig without CONFIG_LTO, with CONFIG_LTO_CLANG, and a third time
>> > > > with CONFIG_THINLTO. If you make changes to the series in follow ups,
>> > > > please drop my tested by tag from the modified patches and I'll help
>> > > > re-test. Some minor feedback on the Kconfig change, but I'll post it
>> > > > off of that patch.
>> > > >
>> > >
>> > > When you say 'virtualized" do you mean QEMU on x86? Or actual
>> > > virtualization on an AArch64 KVM host?
>> >
>> > aarch64 guest on x86_64 host. If you have additional configurations
>> > that are important to you, additional testing help would be
>> > appreciated.
>> >
>>
>> Could you run this on an actual phone? Or does Android already ship
>> with this stuff?
>
> By `this`, if you mean "the LTO series", it has been shipping on
> Android phones for years now, I think it's even required in the latest
> release.
>
> If you mean "the LTO series + mainline" on a phone, well there's the
> android-mainline of https://android.googlesource.com/kernel/common/,
> in which this series was recently removed in order to facilitate
> rebasing Android's patches on ToT-mainline until getting the series
> landed upstream. Bit of a chicken and the egg problem there.
>
> If you mean "the LTO series + mainline + KVM" on a phone; I don't know
> the precise state of aarch64 KVM and Android (Will or Marc would
> know).

If you are lucky enough to have an Android system booting at EL2,
KVM should just works [1], though I haven't tried with this series.

> We did experiment recently with RockPI's for aach64 KVM, IIRC;
> I think Android is tricky as it still requires A64+A32/T32 chipsets,

Which is about 100% of the Android systems at the moment (I don't think
any of the asymmetric SoCs are in the wild yet). It doesn't really
affect
KVM anyway.

M.

[1] with the broken firmware gotchas that I believed to be erradicated
8 years ago, but are still prevalent in the Android world: laughable
PSCI implementation, invalid CNTFRQ_EL0...
--
Who you jivin' with that Cosmik Debris?