linux-kernel - [PATCH v2 1/2] KVM: arm64: Allow userspace to change ID_AA64PFR1

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Date: Tue, 18 Jun 2024 02:38:06 -0400
From: Shaoqin Huang <shahuang@...hat.com>
To: Oliver Upton <oliver.upton@...ux.dev>,
	Marc Zyngier <maz@...nel.org>,
	kvmarm@...ts.linux.dev
Cc: 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 v2 1/2] KVM: arm64: Allow userspace to change ID_AA64PFR1_EL1

Allow userspace to change the guest-visible value of the register with
some severe limitation:

  - No changes to features not virtualized by KVM (MPAM_frac, RAS_frac)
---
 arch/arm64/kvm/sys_regs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 22b45a15d068..bead81867bce 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2306,7 +2306,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 		   ID_AA64PFR0_EL1_GIC |
 		   ID_AA64PFR0_EL1_AdvSIMD |
 		   ID_AA64PFR0_EL1_FP), },
-	ID_SANITISED(ID_AA64PFR1_EL1),
+	ID_WRITABLE(ID_AA64PFR1_EL1, ~(ID_AA64PFR1_EL1_RAS_frac |
+				       ID_AA64PFR1_EL1_MPAM_frac)),
 	ID_UNALLOCATED(4,2),
 	ID_UNALLOCATED(4,3),
 	ID_WRITABLE(ID_AA64ZFR0_EL1, ~ID_AA64ZFR0_EL1_RES0),
-- 
2.40.1