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

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Jon Hunter <jonathanh@nvidia.com>
Cc: Ard Biesheuvel <ardb@kernel.org>,
	linux-arm-kernel@lists.infradead.org, arnd@arndb.de,
	linus.walleij@linaro.org,
	"linux-tegra@vger.kernel.org" <linux-tegra@vger.kernel.org>
Subject: Re: [PATCH 1/6] ARM: spectre-bhb: enable for Cortex-A15
Date: Tue, 24 May 2022 18:03:08 +0100	[thread overview]
Message-ID: <Yo0PzCkBLK5U1nB2@shell.armlinux.org.uk> (raw)
In-Reply-To: <a589f56d-a0e1-328d-e4be-9427342d46b8@nvidia.com>

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@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. :(

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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