linux-kernel - Re: [PATCH] riscv: force __cpu_up_ variables to put in data section

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Date:   Sat, 2 May 2020 17:49:30 +0800
From:   Zong Li <zong.li@...ive.com>
To:     Anup Patel <anup@...infault.org>
Cc:     Atish Patra <atishp@...shpatra.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>
Subject: Re: [PATCH] riscv: force __cpu_up_ variables to put in data section

On Sat, May 2, 2020 at 2:13 PM Anup Patel <anup@...infault.org> wrote:
>
> On Sat, May 2, 2020 at 11:30 AM Zong Li <zong.li@...ive.com> wrote:
> >
> > On Fri, May 1, 2020 at 2:23 AM Atish Patra <atishp@...shpatra.org> wrote:
> > >
> > > On Thu, Apr 30, 2020 at 2:53 AM Zong Li <zong.li@...ive.com> wrote:
> > > >
> > > > Put __cpu_up_stack_pointer and __cpu_up_task_pointer in data section.
> > > > Currently, these two variables are put in bss section, there is a
> > > > potential risk that secondary harts get the uninitialized value before
> > > > main hart finishing the bss clearing. In this case, all secondary
> > > > harts would go through the waiting loop and enable the MMU before
> > > > main hart set up the page table.
> > > >
> > >
> > > That would be only true if you are using random booting protocol with
> > > SBI v0.1 implementation.
> > > With HSM extension in place, all the secondary cores are waiting in
> > > firmware. The booting core
> > > will bring them up one by one from cpu_up method.
> > >
> > > The HSM extension is already available in OpenSBI v0.7 and Linux
> > > kernel 5.7-rc1 onwards.
> >
> > If I understand correctly, the newest kernel still works with earlier
> > OpenSBI than v0.7 or BBL. It seems to me that we need to consider the
> > use cases if we don't limit it to up to OpenSBI v0.7.
>
> I think the commit description should clearly state that the issue will
> manifest only for random booting of multiple HARTs which means it
> will manifest only for BBL and OpenSBI v0.6 (or older).
>

OK. Let me modify the description. Thanks.

> Regards,
> Anup