Commit 459f059b authored by Mark Rutland's avatar Mark Rutland Committed by Marc Zyngier
Browse files

KVM: arm64: Remove VHE host restore of CPACR_EL1.ZEN 



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: default avatarMark Rutland <mark.rutland@arm.com>
Reviewed-by: default avatarMark Brown <broonie@kernel.org>
Tested-by: default avatarMark Brown <broonie@kernel.org>
Acked-by: default avatarWill Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: default avatarOliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-4-mark.rutland@arm.com


Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent 8eca7f6d

arch/arm64/include/asm/kvm_host.h

+0 −1
Original line number Diff line number Diff line
@@ -615,7 +615,6 @@ struct cpu_sve_state { 
struct kvm_host_data {

#define KVM_HOST_DATA_FLAG_HAS_SPE			0

#define KVM_HOST_DATA_FLAG_HAS_TRBE			1

#define KVM_HOST_DATA_FLAG_HOST_SVE_ENABLED		2

#define KVM_HOST_DATA_FLAG_HOST_SME_ENABLED		3

#define KVM_HOST_DATA_FLAG_TRBE_ENABLED			4

#define KVM_HOST_DATA_FLAG_EL1_TRACING_CONFIGURED	5

arch/arm64/kvm/fpsimd.c

+0 −16
Original line number Diff line number Diff line
@@ -65,10 +65,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) 
	fpsimd_save_and_flush_cpu_state();

	*host_data_ptr(fp_owner) = FP_STATE_FREE;



	host_data_clear_flag(HOST_SVE_ENABLED);

	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)

		host_data_set_flag(HOST_SVE_ENABLED);



	if (system_supports_sme()) {

		host_data_clear_flag(HOST_SME_ENABLED);

		if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
@@ -202,18 +198,6 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) 
		 * when needed.

		 */

		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 by kvm_reset_cptr_el2() in the Hyp code, disabling SVE

		 * for EL0.  To avoid spurious traps, restore the trap state

		 * seen by kvm_arch_vcpu_load_fp():

		 */

		if (host_data_test_flag(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);