[5.15,v2,08/10] KVM: arm64: Remove VHE host restore of CPACR_EL1.ZEN

Commit Message

Mark Brown April 2, 2025, 11:20 p.m. UTC

From: Mark Rutland <[e-mail]>

[ Upstream commit 459f059be702056d91537b99a129994aa6ccdd35 ]

When KVM is in VHE mode, the host kernel tries to save and restore the
configuration of CPACR_EL1.ZEN (i.e. CPTR_EL2.ZEN when HCR_EL2.E2H=1)
across kvm_arch_vcpu_load_fp() and kvm_arch_vcpu_put_fp(), since the
configuration may be clobbered by hyp when running a vCPU. This logic is
currently redundant.

The VHE hyp code unconditionally configures CPTR_EL2.ZEN to 0b01 when
returning to the host, permitting host kernel usage of SVE.

Now that the host eagerly saves and unbinds its own FPSIMD/SVE/SME
state, there's no need to save/restore the state of the EL0 SVE trap.
The kernel can safely save/restore state without trapping, as described
above, and will restore userspace state (including trap controls) before
returning to userspace.

Remove the redundant logic.

Signed-off-by: Mark Rutland <[e-mail]>
Reviewed-by: Mark Brown <[e-mail]>
Tested-by: Mark Brown <[e-mail]>
Acked-by: Will Deacon <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Fuad Tabba <[e-mail]>
Cc: Marc Zyngier <[e-mail]>
Cc: Oliver Upton <[e-mail]>
Reviewed-by: Oliver Upton <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Marc Zyngier <[e-mail]>
[Rework for refactoring of where the flags are stored -- broonie]
Signed-off-by: Mark Brown <[e-mail]>
---
 arch/arm64/include/asm/kvm_host.h |  1 -
 arch/arm64/kvm/fpsimd.c           | 15 ---------------
 2 files changed, 16 deletions(-)

Patch

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 06e8d4645ecd..3d4e2396a2d7 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -421,7 +421,6 @@  struct kvm_vcpu_arch {
 #define KVM_ARM64_DEBUG_DIRTY		(1 << 0)
 #define KVM_ARM64_FP_ENABLED		(1 << 1) /* guest FP regs loaded */
 #define KVM_ARM64_FP_HOST		(1 << 2) /* host FP regs loaded */
-#define KVM_ARM64_HOST_SVE_ENABLED	(1 << 4) /* SVE enabled for EL0 */
 #define KVM_ARM64_GUEST_HAS_SVE		(1 << 5) /* SVE exposed to guest */
 #define KVM_ARM64_VCPU_SVE_FINALIZED	(1 << 6) /* SVE config completed */
 #define KVM_ARM64_GUEST_HAS_PTRAUTH	(1 << 7) /* PTRAUTH exposed to guest */
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 1ef9d6cb91ee..1360ddd4137b 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -83,9 +83,6 @@  void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
 	 */
 	fpsimd_save_and_flush_cpu_state();
 	vcpu->arch.flags &= ~KVM_ARM64_FP_HOST;
-
-	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
-		vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED;
 }
 
 /*
@@ -142,18 +139,6 @@  void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
 		}
 
 		fpsimd_save_and_flush_cpu_state();
-	} else if (has_vhe() && system_supports_sve()) {
-		/*
-		 * The FPSIMD/SVE state in the CPU has not been touched, and we
-		 * have SVE (and VHE): CPACR_EL1 (alias CPTR_EL2) has been
-		 * reset to CPACR_EL1_DEFAULT by the Hyp code, disabling SVE
-		 * for EL0.  To avoid spurious traps, restore the trap state
-		 * seen by kvm_arch_vcpu_load_fp():
-		 */
-		if (vcpu->arch.flags & KVM_ARM64_HOST_SVE_ENABLED)
-			sysreg_clear_set(CPACR_EL1, 0, CPACR_EL1_ZEN_EL0EN);
-		else
-			sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0);
 	}
 
 	local_irq_restore(flags);