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

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Message-ID: <a578025ea33108773fe9f3f6e1f180b5@misterjones.org>
Date:   Sat, 21 Nov 2020 11:40:32 +0000
From:   Marc Zyngier <maz@...terjones.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Alistair Delva <adelva@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 00/17] Add support for Clang LTO

On 2020-11-20 23:53, Nick Desaulniers wrote:
> On Fri, Nov 20, 2020 at 3:30 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>> 
>> On Fri, 20 Nov 2020 at 21:19, Nick Desaulniers 
>> <ndesaulniers@...gle.com> wrote:
>> >
>> > On Fri, Nov 20, 2020 at 2:30 AM Ard Biesheuvel <ardb@...nel.org> wrote:
>> > >
>> > > On Thu, 19 Nov 2020 at 00:42, Nick Desaulniers <ndesaulniers@...gle.com> wrote:
>> > > >
>> > > > Thanks for continuing to drive this series Sami.  For the series,
>> > > >
>> > > > Tested-by: Nick Desaulniers <ndesaulniers@...gle.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?