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From: Andrew Murray <andrew.murray@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>
Cc: Andrew Murray <andrew.murray@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v5 1/3] arm64: cpufeature: Extract capped fields
Date: Mon, 27 Jan 2020 11:44:27 +0000
Message-ID: <1580125469-23887-2-git-send-email-andrew.murray@arm.com> (raw)
In-Reply-To: <1580125469-23887-1-git-send-email-andrew.murray@arm.com>

When emulating ID registers there is often a need to cap the version
bits of a feature such that the guest will not use features that do
not yet exist.

Let's add a helper that extracts a field and caps the version to a
given value.

Signed-off-by: Andrew Murray <andrew.murray@arm.com>
---
 arch/arm64/include/asm/cpufeature.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 4261d55..1462fd1 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -447,6 +447,22 @@ cpuid_feature_extract_unsigned_field(u64 features, int field)
 	return cpuid_feature_extract_unsigned_field_width(features, field, 4);
 }
 
+static inline u64 __attribute_const__
+cpuid_feature_cap_signed_field_width(u64 features, int field, int width,
+				     s64 cap)
+{
+	s64 val = cpuid_feature_extract_signed_field_width(features, field,
+							   width);
+	u64 mask = GENMASK_ULL(field + width - 1, field);
+
+	if (val > cap) {
+		features &= ~mask;
+		features |= (cap << field) & mask;
+	}
+
+	return features;
+}
+
 static inline u64 arm64_ftr_mask(const struct arm64_ftr_bits *ftrp)
 {
 	return (u64)GENMASK(ftrp->shift + ftrp->width - 1, ftrp->shift);
-- 
2.7.4

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Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-27 11:44 [PATCH v5 0/3] arm64: perf: Add support for ARMv8.5-PMU 64-bit counters Andrew Murray
2020-01-27 11:44 ` Andrew Murray [this message]
2020-02-11 16:59   ` [PATCH v5 1/3] arm64: cpufeature: Extract capped fields Suzuki Kuruppassery Poulose
2020-01-27 11:44 ` [PATCH v5 2/3] KVM: arm64: limit PMU version to PMUv3 for ARMv8.1 Andrew Murray
2020-02-11 17:55   ` Suzuki Kuruppassery Poulose
2020-02-28 16:51   ` Mark Rutland
2020-02-28 18:22     ` Mark Rutland
2020-01-27 11:44 ` [PATCH v5 3/3] arm64: perf: Add support for ARMv8.5-PMU 64-bit counters Andrew Murray
2020-01-27 12:32   ` Marc Zyngier
2020-01-28  8:53     ` Andrew Murray

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