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From:   Song Liu <song@kernel.org>
Date:   Fri, 8 Sep 2023 15:53:02 -0700
Message-ID: <CAPhsuW7N2ZxO5KubvK4O7EganpGeFFMtx4JGE9sGO5OnzWscgg@mail.gmail.com>
Subject: Re: [PATCH v7 0/4] kexec: Fix kexec_file_load for llvm16 with PGO
To:     Ricardo Ribalda <ribalda@chromium.org>
Cc:     Eric Biederman <ebiederm@xmission.com>,
        Philipp Rudo <prudo@linux.vnet.ibm.com>,
        Dave Young <dyoung@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Tom Rix <trix@redhat.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>, Baoquan He <bhe@redhat.com>,
        Philipp Rudo <prudo@redhat.com>, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org, Ross Zwisler <zwisler@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Simon Horman <horms@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        llvm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org,
        linux-riscv@lists.infradead.org, stable@vger.kernel.org,
        Palmer Dabbelt <palmer@rivosinc.com>
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On Fri, Sep 8, 2023 at 2:52=E2=80=AFPM Ricardo Ribalda <ribalda@chromium.or=
g> wrote:
>
> Hi Song
>
> On Fri, 8 Sept 2023 at 23:48, Song Liu <song@kernel.org> wrote:
> >
> > Hi Ricardo,
> >
> > Thanks for your kind reply.
> >
> > On Fri, Sep 8, 2023 at 2:18=E2=80=AFPM Ricardo Ribalda <ribalda@chromiu=
m.org> wrote:
> > >
> > > Hi Song
> > >
> > > On Fri, 8 Sept 2023 at 01:08, Song Liu <song@kernel.org> wrote:
> > > >
> > > > Hi Ricardo and folks,
> > > >
> > > > On Fri, May 19, 2023 at 7:48=E2=80=AFAM Ricardo Ribalda <ribalda@ch=
romium.org> wrote:
> > > > >
> > > > > When upreving llvm I realised that kexec stopped working on my te=
st
> > > > > platform.
> > > > >
> > > > > The reason seems to be that due to PGO there are multiple .text s=
ections
> > > > > on the purgatory, and kexec does not supports that.
> > > > >
> > > > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > > >
> > > > We are seeing WARNINGs like the following while kexec'ing a PGO and
> > > > LTO enabled kernel:
> > > >
> > > > WARNING: CPU: 26 PID: 110894 at kernel/kexec_file.c:919
> > > > kexec_load_purgatory+0x37f/0x390
> > > >
> > > > AFAICT, the warning was added by this set, and it was triggered whe=
n
> > > > we have many .text sections
> > > > in purgatory.ro. The kexec was actually successful. So I wonder
> > > > whether we really need the
> > > > WARNING here. If we disable LTO (PGO is still enabled), we don't se=
e
> > > > the WARNING any more.
> > > >
> > > > I also tested an older kernel (5.19 based), where we also see many
> > > > .text sections with LTO. It
> > > > kexec()'ed fine. (It doesn't have the WARN_ON() in
> > > > kexec_purgatory_setup_sechdrs).
> > >
> > > You have been "lucky" that the code has chosen the correct start
> > > address, you need to modify the linker script of your kernel to
> > > disable PGO.
> > > You need to backport a patch like this:
> > > https://lore.kernel.org/lkml/CAPhsuW5_qAvV0N3o+hOiAnb1=3DbuJ1pLzqYW9D=
+Bwft6hxJvAeQ@mail.gmail.com/T/#md68b7f832216b0c56bbec0c9b07332e180b9ba2b
> >
> > We already have this commit in our branch. AFAICT, the issue was
> > triggered by LTO. So something like the following seems fixes it
> > (I haven't finished the end-to-end test yet). Does this change make
> > sense to you?
>
> if the end-to-end works, please send it as a patch to the mailing list.
>
> Thanks! :)

OK, it works (AFAICT). Sending the patch.

Thanks,
Song