linux-kernel - [PATCH v5 1/4] KVM: arm64: Disable fields that KVM doesn't know how to handle in ID_AA64PFR1

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Message-Id: <20240723072004.1470688-2-shahuang@redhat.com>
Date: Tue, 23 Jul 2024 03:20:00 -0400
From: Shaoqin Huang <shahuang@...hat.com>
To: Oliver Upton <oliver.upton@...ux.dev>,
	Marc Zyngier <maz@...nel.org>,
	kvmarm@...ts.linux.dev,
	Mark Brown <broonie@...nel.org>
Cc: Eric Auger <eauger@...hat.com>,
	Sebastian Ott <sebott@...hat.com>,
	Cornelia Huck <cohuck@...hat.com>,
	Shaoqin Huang <shahuang@...hat.com>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v5 1/4] KVM: arm64: Disable fields that KVM doesn't know how to handle in ID_AA64PFR1_EL1

For some of the fields in the ID_AA64PFR1_EL1 register, KVM doesn't know
how to handle them right now. So explicitly disable them in the register
accessor, then those fields value will be masked to 0 even if on the
hardware the field value is 1. This is safe because from a UAPI point of
view that read_sanitised_ftr_reg() doesn't yet return a nonzero value
for any of those fields.

This will benifit the migration if the host and VM have different values
when restoring a VM.

Those fields include RNDR_trap, NMI, MTE_frac, GCS, THE, MTEX, DF2, PFAR.

Signed-off-by: Shaoqin Huang <shahuang@...hat.com>
---
 arch/arm64/kvm/sys_regs.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 22b45a15d068..4508288b9d38 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1531,6 +1531,14 @@ static u64 __kvm_read_sanitised_id_reg(const struct kvm_vcpu *vcpu,
 			val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTE);
 
 		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_SME);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_RNDR_trap);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_NMI);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTE_frac);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_GCS);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_THE);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_MTEX);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_DF2);
+		val &= ~ARM64_FEATURE_MASK(ID_AA64PFR1_EL1_PFAR);
 		break;
 	case SYS_ID_AA64ISAR1_EL1:
 		if (!vcpu_has_ptrauth(vcpu))
-- 
2.40.1