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

[Jon Hunter <jonathanh@nvidia.com>]

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@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.

Jon

-- 
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