[PATCH, v2] powerpc: fix hardware PMU exception bug on PowerVM compatibility mode systems

[Leonardo Bras]

On Thu, 2020-02-27 at 10:47 -0300, Desnes A. Nunes do Rosario wrote:
> PowerVM systems running compatibility mode on a few Power8 revisions are
> still vulnerable to the hardware defect that loses PMU exceptions arriving
> prior to a context switch.
> 
> The software fix for this issue is enabled through the CPU_FTR_PMAO_BUG
> cpu_feature bit, nevertheless this bit also needs to be set for PowerVM
> compatibility mode systems.
> 
> Fixes: 68f2f0d431d9ea4 ("powerpc: Add a cpu feature CPU_FTR_PMAO_BUG")
> Signed-off-by: Desnes A. Nunes do Rosario <desnesn at linux.ibm.com>
> ---
>  arch/powerpc/kernel/cputable.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
> index e745abc5457a..245be4fafe13 100644
> --- a/arch/powerpc/kernel/cputable.c
> +++ b/arch/powerpc/kernel/cputable.c
> @@ -2193,11 +2193,13 @@ static struct cpu_spec * __init setup_cpu_spec(unsigned long offset,
>  		 * oprofile_cpu_type already has a value, then we are
>  		 * possibly overriding a real PVR with a logical one,
>  		 * and, in that case, keep the current value for
> -		 * oprofile_cpu_type.
> +		 * oprofile_cpu_type. Futhermore, let's ensure that the
> +		 * fix for the PMAO bug is enabled on compatibility mode.
>  		 */
>  		if (old.oprofile_cpu_type != NULL) {
>  			t->oprofile_cpu_type = old.oprofile_cpu_type;
>  			t->oprofile_type = old.oprofile_type;
> +			t->cpu_features |= old.cpu_features & CPU_FTR_PMAO_BUG;
>  		}
>  	}
>  

Looks good to me.

Reviewed-by: Leonardo Bras <leonardo at linux.ibm.com>
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