[PATCH 07/18] arm64: Add system_supports_hvo

[James Houghton]

Track HVO compatibility as its own system feature. If every boot CPU
supports it, later onlining a CPU that doesn't support it won't be
allowed.

HVO requires BBM Level 2 no abort for the block -> table transitions
when optimizing the vmemmap, and it requires hardware AF management to
avoid taking page faults on the !AF translation that is installed as
part of the RW table -> RO + new OA table transitions.

Another possibility would be to disable HVO if an incompatible CPU were
onlined; I haven't done this.

Signed-off-by: James Houghton <jthoughton at google.com>
---
 arch/arm64/include/asm/cpucaps.h    |  2 ++
 arch/arm64/include/asm/cpufeature.h |  5 +++++
 arch/arm64/kernel/cpufeature.c      | 16 ++++++++++++++++
 arch/arm64/tools/cpucaps            |  1 +
 4 files changed, 24 insertions(+)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 25c61cda901c..6db3ef827f86 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -75,6 +75,8 @@ cpucap_is_possible(const unsigned int cap)
 		return IS_ENABLED(CONFIG_HW_PERF_EVENTS);
 	case ARM64_HAS_LSUI:
 		return IS_ENABLED(CONFIG_ARM64_LSUI);
+	case ARM64_HVO_COMPATIBLE:
+		return IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP);
 	}
 
 	return true;
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index e818ad1b56e2..a62c284962cf 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -885,6 +885,11 @@ static inline bool system_supports_bbml2_noabort(void)
 	return alternative_has_cap_unlikely(ARM64_HAS_BBML2_NOABORT);
 }
 
+static inline bool system_supports_hvo(void)
+{
+	return alternative_has_cap_unlikely(ARM64_HVO_COMPATIBLE);
+}
+
 int do_emulate_mrs(struct pt_regs *regs, u32 sys_reg, u32 rt);
 bool try_emulate_mrs(struct pt_regs *regs, u32 isn);
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 9a22df0c5120..3b9224b99a5f 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2172,6 +2172,16 @@ static bool has_bbml2_noabort(const struct arm64_cpu_capabilities *caps, int sco
 	return cpu_supports_bbml2_noabort();
 }
 
+static bool hvo_compatible(const struct arm64_cpu_capabilities *caps, int scope)
+{
+	/*
+	 * We need BBML2 to support Block -> Table transitions without taking
+	 * faults, and we need HW AF support to support changing the OA without
+	 * taking faults.
+	 */
+	return cpu_supports_bbml2_noabort() && supports_hw_af(scope);
+}
+
 static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused)
 {
 	/*
@@ -3067,6 +3077,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.type = ARM64_CPUCAP_EARLY_LOCAL_CPU_FEATURE,
 		.matches = has_bbml2_noabort,
 	},
+	{
+		.desc = "HugeTLB Vmemmap Optimization Support",
+		.capability = ARM64_HVO_COMPATIBLE,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = hvo_compatible,
+	},
 	{
 		.desc = "52-bit Virtual Addressing for KVM (LPA2)",
 		.capability = ARM64_HAS_LPA2,
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 9b85a84f6fd4..630953d59c52 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -70,6 +70,7 @@ HAS_VIRT_HOST_EXTN
 HAS_WFXT
 HAS_XNX
 HAFT
+HVO_COMPATIBLE
 HW_DBM
 KVM_HVHE
 KVM_PROTECTED_MODE
-- 
2.55.0.795.g602f6c329a-goog