Re: [PATCH v2 1/5] arm64: cpufeature: Add scope for capability check

From: Suzuki K Poulose
Date: Wed Apr 20 2016 - 08:35:36 EST

On 20/04/16 12:28, Will Deacon wrote:
On Mon, Apr 18, 2016 at 05:35:30PM +0100, Suzuki K Poulose wrote:
Add scope parameter to the arm64_cpu_capabilities::matches(), so that
this can be reused for checking the capability on a given CPU vs the
system wide. The system uses the default scope associated with the
capability for initialising the CPU_HWCAPs and ELF_HWCAPs.

+/* scope of capability check */
+enum {

I think I actually prefer the GLOBAL/LOCAL naming, since SYSTEM is going
to be the scope you want when talking about all CPUs. Or maybe just


We might want a preemptible() check when probing SCOPE_CPU properties,

Good point. The current users are all calling them from the CPU init phase,
where it is not preemptible. But it would be good to add a check to make sure
nobody violates this condition. Also, will add a comment for
"this_cpu_has_cap()" API to call it under !preemptible() state.

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 8c46621..db392c5 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -71,7 +71,9 @@ DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);

/* meta feature for alternatives */
static bool __maybe_unused
-cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry);
+cpufeature_pan_not_uao(const struct arm64_cpu_capabilities *entry, int __unused);
+static u64 __raw_read_system_reg(u32 sys_id);

Can we not reorder the functions in this file to avoid the internal forward

We can. I had that in my initial version, but the patch looked a bit more complicated
with the code movement. I will bring it back and get rid of the declaration.