From: Mark Rutland <mark.rutland@xxxxxxx>
[ Upstream commit 407a99c4654e8ea65393f412c421a55cac539f5b ]
When KVM is in VHE mode, the host kernel tries to save and restore the
configuration of CPACR_EL1.SMEN (i.e. CPTR_EL2.SMEN 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
has historically been broken, and is currently redundant.
This logic was originally introduced in commit:
861262ab86270206 ("KVM: arm64: Handle SME host state when running guests")
At the time, the VHE hyp code would reset CPTR_EL2.SMEN to 0b00 when
returning to the host, trapping host access to SME state. Unfortunately,
this was unsafe as the host could take a softirq before calling
kvm_arch_vcpu_put_fp(), and if a softirq handler were to use kernel mode
NEON the resulting attempt to save the live FPSIMD/SVE/SME state would
result in a fatal trap.
That issue was limited to VHE mode. For nVHE/hVHE modes, KVM always
saved/restored the host kernel's CPACR_EL1 value, and configured
CPTR_EL2.TSM to 0b0, ensuring that host usage of SME would not be
trapped.
The issue above was incidentally fixed by commit:
375110ab51dec5dc ("KVM: arm64: Fix resetting SME trap values on reset for (h)VHE")
That commit changed the VHE hyp code to configure CPTR_EL2.SMEN to 0b01
when returning to the host, permitting host kernel usage of SME,
avoiding the issue described above. At the time, this was not identified
as a fix for commit 861262ab86270206.
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 SME 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@xxxxxxx>
Reviewed-by: Mark Brown <broonie@xxxxxxxxxx>
Tested-by: Mark Brown <broonie@xxxxxxxxxx>
Acked-by: Will Deacon <will@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Fuad Tabba <tabba@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Oliver Upton <oliver.upton@xxxxxxxxx>
Reviewed-by: Oliver Upton <oliver.upton@xxxxxxxxx>
Link: https://lore.kernel.org/r/20250210195226.1215254-5-mark.rutland@xxxxxxx
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
[Update for rework of flags storage -- broonie]
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
arch/arm64/include/asm/kvm_host.h | 2 --
arch/arm64/kvm/fpsimd.c | 23 -----------------------
2 files changed, 25 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 9c1056d6f6859522dcee4b8c4e4804a7abac93d5..27c53b603d693d1cfe8d81f94a59d3afb665be8e 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -717,8 +717,6 @@ struct kvm_vcpu_arch {
/* vcpu running in HYP context */
#define VCPU_HYP_CONTEXT __vcpu_single_flag(iflags, BIT(7))
-/* SME enabled for EL0 */
-#define HOST_SME_ENABLED __vcpu_single_flag(sflags, BIT(1))
/* Physical CPU not in supported_cpus */
#define ON_UNSUPPORTED_CPU __vcpu_single_flag(sflags, BIT(2))
/* WFIT instruction trapped */
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index f1fe7abbcb83393e7c3402405bb7b1fdbf6024ff..0492a1fc718130934f8bada836fe42bea6db7abb 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -87,12 +87,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
*/
fpsimd_save_and_flush_cpu_state();
vcpu->arch.fp_state = FP_STATE_FREE;
-
- if (system_supports_sme()) {
- vcpu_clear_flag(vcpu, HOST_SME_ENABLED);
- if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
- vcpu_set_flag(vcpu, HOST_SME_ENABLED);
- }
}
/*
@@ -157,23 +151,6 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu)
local_irq_save(flags);
- /*
- * If we have VHE then the Hyp code will reset CPACR_EL1 to
- * the default value and we need to reenable SME.
- */
- if (has_vhe() && system_supports_sme()) {
- /* Also restore EL0 state seen on entry */
- if (vcpu_get_flag(vcpu, HOST_SME_ENABLED))
- sysreg_clear_set(CPACR_EL1, 0,
- CPACR_EL1_SMEN_EL0EN |
- CPACR_EL1_SMEN_EL1EN);
- else
- sysreg_clear_set(CPACR_EL1,
- CPACR_EL1_SMEN_EL0EN,
- CPACR_EL1_SMEN_EL1EN);
- isb();
- }
-
if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
if (vcpu_has_sve(vcpu)) {
__vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR);
--
2.39.5
