[PATCH 1/6] ARM: spectre-bhb: enable for Cortex-A15

[Ard Biesheuvel]

On Tue, 7 Jun 2022 at 16:30, Jon Hunter <jonathanh at nvidia.com> wrote:
>
>
> On 24/05/2022 18:03, Russell King (Oracle) wrote:
> > On Tue, May 24, 2022 at 03:50:17PM +0100, Jon Hunter wrote:
> >> Hi Ard,
> >>
> >> On 28/03/2022 14:47, Ard Biesheuvel wrote:
> >>> The Spectre-BHB mitigations were inadvertently left disabled for
> >>> Cortex-A15, due to the fact that cpu_v7_bugs_init() is not called in
> >>> that case. So fix that.
> >>>
> >>> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> >>> ---
> >>>    arch/arm/mm/proc-v7-bugs.c | 1 +
> >>>    1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/arch/arm/mm/proc-v7-bugs.c b/arch/arm/mm/proc-v7-bugs.c
> >>> index 06dbfb968182..fb9f3eb6bf48 100644
> >>> --- a/arch/arm/mm/proc-v7-bugs.c
> >>> +++ b/arch/arm/mm/proc-v7-bugs.c
> >>> @@ -288,6 +288,7 @@ void cpu_v7_ca15_ibe(void)
> >>>    {
> >>>     if (check_spectre_auxcr(this_cpu_ptr(&spectre_warned), BIT(0)))
> >>>             cpu_v7_spectre_v2_init();
> >>> +   cpu_v7_spectre_bhb_init();
> >>>    }
> >>>    void cpu_v7_bugs_init(void)
> >>
> >>
> >> Since this patch has been merged, I am seeing a ton of messages when booting
> >> Linux on tegra124-jetson-tk1 ...
> >>
> >> [ 1233.327547] CPU0: Spectre BHB: using loop workaround
> >> [ 1233.327795] CPU1: Spectre BHB: using loop workaround
> >> [ 1233.328270] CPU1: Spectre BHB: using loop workaround
> >
> > Now that you mention this, I vaguely remember some email on the list a
> > while ago about this being caused by something like cpuidle - but I'm
> > unable to find it now.
> >
> >> [0] https://lore.kernel.org/linux-arm-kernel/20220519161310.1489625-1-dmitry.osipenko@collabora.com/T/
> >
> > That was probably it.
> >
> > We can't really do this for the other print, because the system status
> > can change as a result of CPUs being brought online. :(
> >
>
> Does it make sense to only print the message if/when the method changes
> as opposed to every time the CPUs are brought online? That way, there
> would still be at least one print showing the current method. I believe
> that is what Ard had proposed.
>

A fix for this issue is already in linux-next:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=bafa10435c4f34f4b9bda8fc7ee6e4330ebca3ea