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

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[ 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.

Bug: 357781595
Bug: 411040189
Change-Id: I43bf5587223aae54caf9389eb3de17f155043d96
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Acked-by: Will 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: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-4-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
[Rework for refactoring of where the flags are stored -- broonie]
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Fuad Tabba <tabba@google.com>
This commit is contained in:
Mark Rutland
2025-02-10 19:52:21 +00:00
committed by Will Deacon
parent f012246148
commit 5f2af6c19e
2 changed files with 0 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm64/include/asm/kvm_host.h
View File

@@ -1060,8 +1060,6 @@ struct kvm_vcpu_arch {
/* pKVM host vcpu state is dirty, needs resync (nVHE-only) */
#define PKVM_HOST_STATE_DIRTY __vcpu_single_flag(iflags, BIT(7))
/* 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 */

16
arch/arm64/kvm/fpsimd.c
View File

@@ -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;
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_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 (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);