Patch "KVM: arm64: Remove VHE host restore of CPACR_EL1.ZEN" has been added to the 6.12-stable tree

[gregkh at linuxfoundation.org]

This is a note to let you know that I've just added the patch titled

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

to the 6.12-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-arm64-remove-vhe-host-restore-of-cpacr_el1.zen.patch
and it can be found in the queue-6.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.


>From broonie at kernel.org Thu Mar 20 17:13:41 2025
From: Mark Brown <broonie at kernel.org>
Date: Fri, 21 Mar 2025 00:13:00 +0000
Subject: KVM: arm64: Remove VHE host restore of CPACR_EL1.ZEN
To: Greg Kroah-Hartman <gregkh at linuxfoundation.org>,  Marc Zyngier <maz at kernel.org>, Oliver Upton <oliver.upton at linux.dev>,  Joey Gouly <joey.gouly at arm.com>, Suzuki K Poulose <suzuki.poulose at arm.com>,  Catalin Marinas <catalin.marinas at arm.com>, Will Deacon <will at kernel.org>
Cc: linux-arm-kernel at lists.infradead.org, kvmarm at lists.linux.dev,  linux-kernel at vger.kernel.org, stable at vger.kernel.org,  Mark Brown <broonie at kernel.org>, Mark Rutland <mark.rutland at arm.com>,  Fuad Tabba <tabba at google.com>
Message-ID: <20250321-stable-sve-6-12-v2-4-417ca2278d18 at kernel.org>

From: Mark Rutland <mark.rutland at arm.com>

[ 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 <mark.rutland at arm.com>
Reviewed-by: Mark Brown <broonie at kernel.org>
Tested-by: Mark Brown <broonie at kernel.org>
Acked-by: Will Deacon <will at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Fuad Tabba <tabba at google.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Oliver Upton <oliver.upton at linux.dev>
Reviewed-by: Oliver Upton <oliver.upton at linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-4-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz at kernel.org>
[Rework for refactoring of where the flags are stored -- broonie]
Signed-off-by: Mark Brown <broonie at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 arch/arm64/include/asm/kvm_host.h |    2 --
 arch/arm64/kvm/fpsimd.c           |   16 ----------------
 2 files changed, 18 deletions(-)

--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -891,8 +891,6 @@ struct kvm_vcpu_arch {
 /* Save TRBE context if active  */
 #define DEBUG_STATE_SAVE_TRBE	__vcpu_single_flag(iflags, BIT(6))
 
-/* SVE enabled for host EL0 */
-#define HOST_SVE_ENABLED	__vcpu_single_flag(sflags, BIT(0))
 /* SME enabled for EL0 */
 #define HOST_SME_ENABLED	__vcpu_single_flag(sflags, BIT(1))
 /* Physical CPU not in supported_cpus */
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -65,10 +65,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vc
 	fpsimd_save_and_flush_cpu_state();
 	*host_data_ptr(fp_owner) = FP_STATE_FREE;
 
-	vcpu_clear_flag(vcpu, HOST_SVE_ENABLED);
-	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
-		vcpu_set_flag(vcpu, HOST_SVE_ENABLED);
-
 	if (system_supports_sme()) {
 		vcpu_clear_flag(vcpu, HOST_SME_ENABLED);
 		if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
@@ -202,18 +198,6 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcp
 		 * 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 (vcpu_get_flag(vcpu, 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);


Patches currently in stable-queue which might be from broonie at kernel.org are

queue-6.12/kvm-arm64-calculate-cptr_el2-traps-on-activating-traps.patch
queue-6.12/regulator-check-that-dummy-regulator-has-been-probed-before-using-it.patch
queue-6.12/kvm-arm64-eagerly-switch-zcr_el-1-2.patch
queue-6.12/kvm-arm64-mark-some-header-functions-as-inline.patch
queue-6.12/kvm-arm64-remove-host-fpsimd-saving-for-non-protected-kvm.patch
queue-6.12/regulator-dummy-force-synchronous-probing.patch
queue-6.12/kvm-arm64-refactor-exit-handlers.patch
queue-6.12/kvm-arm64-unconditionally-save-flush-host-fpsimd-sve-sme-state.patch
queue-6.12/kvm-arm64-remove-vhe-host-restore-of-cpacr_el1.smen.patch
queue-6.12/kvm-arm64-remove-vhe-host-restore-of-cpacr_el1.zen.patch