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

[Ard Biesheuvel]

On Tue, 24 May 2022 at 16:50, Jon Hunter <jonathanh at nvidia.com> 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 ...
>

Thanks for the report. The good news is that the Spectre BHB
protection is finally taking effect on your system.

> [ 1233.327547] CPU0: Spectre BHB: using loop workaround
> [ 1233.327795] CPU1: Spectre BHB: using loop workaround
> [ 1233.328270] CPU1: Spectre BHB: using loop workaround
> [ 1233.328700] CPU1: Spectre BHB: using loop workaround
> [ 1233.355477] CPU2: Spectre BHB: using loop workaround
> ** 7 printk messages dropped **
> [ 1233.366271] CPU0: Spectre BHB: using loop workaround
> [ 1233.366580] CPU0: Spectre BHB: using loop workaround
> [ 1233.366815] CPU1: Spectre BHB: using loop workaround
> [ 1233.405475] CPU1: Spectre BHB: using loop workaround
> [ 1233.405874] CPU0: Spectre BHB: using loop workaround
> [ 1233.406041] CPU1: Spectre BHB: using loop workaround
> ** 1 printk messages dropped **
>
> This is significantly increasing the boot time and causing failures if
> the boot takes too long.
>
> I see that Dmitry has posted a fix for one of these cases [0], but the
> above also needs to be fixed.
>

Agreed.

Do we have any idea why this init hook is being called so often? Is
this expected on systems that do agressive suspend/resume for power
management, or is there another existing issue here that is just
coming to light due to the newly added printk() ?