On Wed, Sep 18, 2019 at 03:20:41PM +0100, Suzuki K Poulose wrote:

On 18/09/2019 14:19, Jia He wrote:

quoted

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index c96ffa4722d3..206b6e3954cf 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h

@@ -390,6 +390,7 @@ extern DECLARE_BITMAP(boot_capabilities, ARM64_NPATCHABLE);
  	for_each_set_bit(cap, cpu_hwcaps, ARM64_NCAPS)
  bool this_cpu_has_cap(unsigned int cap);
+bool cpu_has_hw_af(void);
  void cpu_set_feature(unsigned int num);
  bool cpu_have_feature(unsigned int num);
  unsigned long cpu_get_elf_hwcap(void);

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index b1fdc486aed8..c5097f58649d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -1141,6 +1141,12 @@ static bool has_hw_dbm(const struct arm64_cpu_capabilities *cap,
  	return true;
  }
+/* Decouple AF from AFDBM. */
+bool cpu_has_hw_af(void)
+{

Sorry for not having asked this earlier. Are we interested in,

"whether *this* CPU has AF support ?" or "whether *at least one*
CPU has the AF support" ? The following code does the former.

quoted

+	return (read_cpuid(ID_AA64MMFR1_EL1) & 0xf);

In a non-preemptible context, the former is ok (per-CPU).

-- 
Catalin

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