linux-kernel - [PATCH v3 14/15] arch/arm64: Introduce a capability to tell whether 16-bit VMID is available

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Date:   Wed, 24 Jul 2019 17:25:33 +0100
From:   Julien Grall <julien.grall@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu
Cc:     james.morse@....com, marc.zyngier@....com, julien.thierry@....com,
        suzuki.poulose@....com, catalin.marinas@....com,
        will.deacon@....com, Julien Grall <julien.grall@....com>
Subject: [PATCH v3 14/15] arch/arm64: Introduce a capability to tell whether 16-bit VMID is available

At the moment, the function kvm_get_vmid_bits() is looking up for the
sanitized value of ID_AA64MMFR1_EL1 and extract the information
regarding the number of VMID bits supported.

This is fine as the function is mainly used during VMID roll-over. New
use in a follow-up patch will require the function to be called a every
context switch so we want the function to be more efficient.

A new capability is introduced to tell whether 16-bit VMID is
available.

Signed-off-by: Julien Grall <julien.grall@....com>

---
    Changes in v3:
        - Patch added
---
 arch/arm64/include/asm/cpucaps.h | 3 ++-
 arch/arm64/include/asm/kvm_mmu.h | 4 +---
 arch/arm64/kernel/cpufeature.c   | 9 +++++++++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index f19fe4b9acc4..af8ab758b252 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -52,7 +52,8 @@
 #define ARM64_HAS_IRQ_PRIO_MASKING		42
 #define ARM64_HAS_DCPODP			43
 #define ARM64_WORKAROUND_1463225		44
+#define ARM64_HAS_16BIT_VMID			45
 
-#define ARM64_NCAPS				45
+#define ARM64_NCAPS				46
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index befe37d4bc0e..2ce8055a84b8 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -413,9 +413,7 @@ static inline void __kvm_extend_hypmap(pgd_t *boot_hyp_pgd,
 
 static inline unsigned int kvm_get_vmid_bits(void)
 {
-	int reg = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
-
-	return (cpuid_feature_extract_unsigned_field(reg, ID_AA64MMFR1_VMIDBITS_SHIFT) == 2) ? 16 : 8;
+	return cpus_have_const_cap(ARM64_HAS_16BIT_VMID) ? 16 : 8;
 }
 
 /*
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index f29f36a65175..b401e56af35a 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1548,6 +1548,15 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.min_field_value = 1,
 	},
 #endif
+	{
+		.capability = ARM64_HAS_16BIT_VMID,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.sys_reg = SYS_ID_AA64MMFR1_EL1,
+		.field_pos = ID_AA64MMFR1_VMIDBITS_SHIFT,
+		.sign = FTR_UNSIGNED,
+		.min_field_value = ID_AA64MMFR1_VMIDBITS_16,
+		.matches = has_cpuid_feature,
+	},
 	{},
 };
 
-- 
2.11.0