powerpc: fix hardware PMU exception bug on PowerVM compatibility mode systems
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Message ID 20200214001905.20065-1-desnesn@linux.ibm.com
State New
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  • powerpc: fix hardware PMU exception bug on PowerVM compatibility mode systems
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Commit Message

Desnes A. Nunes do Rosario Feb. 14, 2020, 12:19 a.m. UTC
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@linux.ibm.com>
---
 arch/powerpc/kernel/cputable.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Leonardo Bras Feb. 15, 2020, 6:26 a.m. UTC | #1
Hello Desnes, thanks for the patch.

On Thu, 2020-02-13 at 21:19 -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@linux.ibm.com>
> ---
>  arch/powerpc/kernel/cputable.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
> index e745abc5457a..5bfef6263dfb 100644
> --- a/arch/powerpc/kernel/cputable.c
> +++ b/arch/powerpc/kernel/cputable.c
> @@ -2198,6 +2198,8 @@ static struct cpu_spec * __init setup_cpu_spec(unsigned long offset,
>  		if (old.oprofile_cpu_type != NULL) {
>  			t->oprofile_cpu_type = old.oprofile_cpu_type;
>  			t->oprofile_type = old.oprofile_type;
> +			if (old.cpu_features & CPU_FTR_PMAO_BUG)
> +				t->cpu_features |= CPU_FTR_PMAO_BUG;
>  		}
>  	}
>  

What are your thoughts about doing:
        t->cpu_features |=  old.cpu_features & CPU_FTR_PMAO_BUG;

Also, I would recommend adding a short comment on top of the added
lines explaining why it is needed. 

Best regards,
Leonardo Bras

Patch
diff mbox series

diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index e745abc5457a..5bfef6263dfb 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -2198,6 +2198,8 @@  static struct cpu_spec * __init setup_cpu_spec(unsigned long offset,
 		if (old.oprofile_cpu_type != NULL) {
 			t->oprofile_cpu_type = old.oprofile_cpu_type;
 			t->oprofile_type = old.oprofile_type;
+			if (old.cpu_features & CPU_FTR_PMAO_BUG)
+				t->cpu_features |= CPU_FTR_PMAO_BUG;
 		}
 	}