arm64: Check for errata before evaluating cpu features
PATCH 1/1 arm64: Check for errata before evaluating cpu features
Since commit d3aec8a28be3b8 ("arm64: capabilities: Restrict KPTI detection to boot-time CPUs") we rely on errata flags being already populated during feature enumeration. The order of errata and features was flipped as part of commit ed478b3f9e4a ("arm64:
capabilities: Group handling of features and errata workarounds").
Return to the orginal order of errata and feature evaluation to ensure errata flags are present during feature evaluation.
detection to boot-time CPUs")
--- arch/arm64/kernel/cpufeature.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
arch/arm64/kernel/cpufeature.c +2 -2
@@ -1351,9 +1351,9 @@ static void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,static void update_cpu_capabilities (u16 scope_mask) { -__update_cpu_capabilities (arm64_features, scope_mask,"detected:" );__update_cpu_capabilities (arm64_errata, scope_mask,"enabling workaround for" ); +__update_cpu_capabilities (arm64_features, scope_mask,"detected:" ); }static int __enable_cpu_capability (void *arg)
@@ -1408,8 +1408,8 @@ __enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps,static void __init enable_cpu_capabilities (u16 scope_mask) { -__enable_cpu_capabilities (arm64_features, scope_mask);__enable_cpu_capabilities (arm64_errata, scope_mask); +__enable_cpu_capabilities (arm64_features, scope_mask); }/*
Signature · 1 line
2.18.0
Quoted 6 lines · Dirk Mueller
Since commit
d3aec8a28be3b8("arm64: capabilities: Restrict KPTI detection to boot-time CPUs") we rely on errata flags being already populated during feature enumeration. The order of errata and features was flipped as part of commited478b3f9e4a("arm64:
capabilities: Group handling of features and errata workarounds").
Quoted 8 lines
Return to the orginal order of errata and feature evaluation to ensure errata flags are present during feature evaluation.
Fixes d3aec8a28be3b8 ("arm64: capabilities: Restrict KPTIdetection to boot-time CPUs")
CC Suzuki K Poulose <[email protected]>CC Marc Zyngier <[email protected]>Signed-off-by Dirk Mueller <[email protected]>
It would be good to add "Fixes: ed478b3f9e4a" (instead), just to make sure this gets fixed everywhere the original problem appears.
Quoted 20 lines
--- arch/arm64/kernel/cpufeature.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)arch/arm64/kernel/cpufeature.c +1
-1@@ -1351,9 +1351,9 @@ static void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,static void update_cpu_capabilities (u16 scope_mask) { -__update_cpu_capabilities (arm64_features, scope_mask,"detected:" );__update_cpu_capabilities (arm64_errata, scope_mask,"enabling workaround for" ); +__update_cpu_capabilities (arm64_features, scope_mask,"detected:" ); }static int __enable_cpu_capability (void *arg)
arch/arm64/kernel/cpufeature.c __enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps, · line 1412
Quoted 6 lines
arch/arm64/kernel/cpufeature.c +1
-1@@ -1408,8 +1408,8 @@ __enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps,static void __init enable_cpu_capabilities (u16 scope_mask) { -__enable_cpu_capabilities (arm64_features, scope_mask);__enable_cpu_capabilities (arm64_errata, scope_mask); +__enable_cpu_capabilities (arm64_features, scope_mask);
Quoted 34 lines · Suzuki K Poulose
Quoted 6 lines · Dirk Mueller
Since commit
d3aec8a28be3b8("arm64: capabilities: Restrict KPTI detection to boot-time CPUs") we rely on errata flags being already populated during feature enumeration. The order of errata and features was flipped as part of commited478b3f9e4a("arm64:
capabilities: Group handling of features and errata workarounds").Quoted 8 lines
Return to the orginal order of errata and feature evaluation to ensure errata flags are present during feature evaluation.
Fixes d3aec8a28be3b8 ("arm64: capabilities: Restrict KPTIdetection to boot-time CPUs")
CC Suzuki K Poulose <[email protected]>CC Marc Zyngier <[email protected]>Signed-off-by Dirk Mueller <[email protected]>It would be good to add "Fixes:
ed478b3f9e4a" (instead), just to make sure this gets fixed everywhere the original problem appears.Quoted 15 lines
--- arch/arm64/kernel/cpufeature.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)arch/arm64/kernel/cpufeature.c +1
-1@@ -1351,9 +1351,9 @@ static void __update_cpu_capabilities(const struct arm64_cpu_capabilities *caps,static void update_cpu_capabilities (u16 scope_mask) { -__update_cpu_capabilities (arm64_features, scope_mask,"detected:" );__update_cpu_capabilities (arm64_errata, scope_mask,"enabling workaround for" ); +__update_cpu_capabilities (arm64_features, scope_mask,"detected:" );
Quoted 8 lines
arch/arm64/kernel/cpufeature.c __enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps, · line 1411
Quoted 8 lines
arch/arm64/kernel/cpufeature.c +1
-1}static int __enable_cpu_capability (void *arg)@@ -1408,8 +1408,8 @@ __enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps,static void __init enable_cpu_capabilities (u16 scope_mask) { -__enable_cpu_capabilities (arm64_features, scope_mask);__enable_cpu_capabilities (arm64_errata, scope_mask); +__enable_cpu_capabilities (arm64_features, scope_mask);
I forget why these were originally reordered in ed478b3f9e4a. Was there any real reason for it?
I also notice in that commit that after the detection pass, we set things up (in update_cpu_capabilities(), enable_cpu_capabilities()) in the order errata, features. Does this matter for anything?
Cheers
---Dave
Quoted 8 lines
Reviewed-by Suzuki K Poulose <[email protected]>_______________________________________________
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Dave,
Quoted 17 lines · Dave Martin
Quoted 16 lines · Suzuki K Poulose
Quoted 14 lines · Dirk Mueller
Since commit
d3aec8a28be3b8("arm64: capabilities: Restrict KPTI detection to boot-time CPUs") we rely on errata flags being already populated during feature enumeration. The order of errata and features was flipped as part of commited478b3f9e4a("arm64:
capabilities: Group handling of features and errata workarounds").Return to the orginal order of errata and feature evaluation to ensure errata flags are present during feature evaluation.
Fixes d3aec8a28be3b8 ("arm64: capabilities: Restrict KPTIdetection to boot-time CPUs")
CC Suzuki K Poulose <[email protected]>CC Marc Zyngier <[email protected]>Signed-off-by Dirk Mueller <[email protected]>
Quoted 7 lines
Quoted 3 lines
It would be good to add "Fixes:
ed478b3f9e4a" (instead), just to make sure this gets fixed everywhere the original problem appears.I forget why these were originally reordered in
ed478b3f9e4a. Was there any real reason for it?
No, there was no real reason for it. We have always detected the cpu local errata first and all features were system wide. So that ensured that the errata are detected before features. With the introduction of cpu local features, it was a random order until we realised this issue.
That said, this exposes a problem with the current infrastructure where, if there are local capabilities that depend on other local capabilities. On a heterogeneous system, there is no guarantee on the order in which the CPUs turn up and thus detect the capabilities. In this case, this patch wouldn't work if we were dealing with a heterogeneous system.
The solution would be to use cpu local and system wide versions of the same capability and use the cpu-local capabilities to decide the system capability.
i.e, here KPTI needs two caps :
a) CPU_NEEDS_KPTI - Local CPU capability to detect the local CPU which needs KPTRI
b) SYSTEM_NEEDS_KPTI - System wide capability, which can be turned on iff we have CPU_NEEDS_KPTI && !CAVIUM_ERRATA.
Quoted 4 lines
I also notice in that commit that after the detection pass, we set things up (in
update_cpu_capabilities(),enable_cpu_capabilities()) in the order errata, features. Does this matter for anything?
None that I am aware of. But logically that sounds like a better option.
Suzuki