Oliver Upton <oliver.upton@xxxxxxxxx> writes:
Hi Colton,
On Mon, Apr 22, 2024 at 06:17:16PM +0000, Colton Lewis wrote:
@@ -2653,6 +2653,27 @@
[KVM,ARM] Allow use of GICv4 for direct injection of
LPIs.
+ kvm-arm.wfe_trap_policy=
+ [KVM,ARM] Control when to set wfe instruction trap.
nitpick: when referring to the instruction, please capitalize it.
Also, it doesn't hurt to be verbose here and say this cmdline option
"Controls the WFE instruction trap behavior for KVM VMs"
I say this because there is a separate set of trap controls that allow
WFE or WFI to execute in EL0 (i.e. host userspace).
Will do.
+ trap: set wfe instruction trap
+
+ notrap: clear wfe instruction trap
+
+ default: set wfe instruction trap only if multiple
+ tasks are running on the CPU
I would strongly prefer we not make any default behavior user-visible.
The default KVM behavior can (and will) change in the future.
Only the absence of an explicit trap / notrap policy should fall back to
KVM's default heuristics.
Makes sense to me. Will do.
-static inline void vcpu_clear_wfx_traps(struct kvm_vcpu *vcpu)
+static inline void vcpu_clear_wfe_trap(struct kvm_vcpu *vcpu)
{
vcpu->arch.hcr_el2 &= ~HCR_TWE;
+}
+
+static inline void vcpu_clear_wfi_trap(struct kvm_vcpu *vcpu)
+{
if (atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
vcpu->kvm->arch.vgic.nassgireq)
vcpu->arch.hcr_el2 &= ~HCR_TWI;
@@ -119,12 +123,28 @@ static inline void vcpu_clear_wfx_traps(struct
kvm_vcpu *vcpu)
vcpu->arch.hcr_el2 |= HCR_TWI;
}
This helper definitely does not do as it says on the tin. It ignores the
policy requested on the command line and conditionally *sets* TWI. If
the operator believes they know best and ask for a particular trap policy
KVM should uphold it unconditionally. Even if they've managed to shoot
themselves in the foot.
Will do. I was only splitting up what the existing helper did here.
@@ -423,6 +425,12 @@ void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
}
+static bool kvm_should_clear_wfx_trap(enum kvm_wfx_trap_policy p)
+{
+ return (p == KVM_WFX_NOTRAP && kvm_vgic_global_state.has_gicv4)
+ || (p == KVM_WFX_NOTRAP_SINGLE_TASK && single_task_running());
+}
style nitpick: operators should always go on the preceding line for a
multi-line statement.
Will do.
void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
{
struct kvm_s2_mmu *mmu;
@@ -456,10 +464,15 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int
cpu)
if (kvm_arm_is_pvtime_enabled(&vcpu->arch))
kvm_make_request(KVM_REQ_RECORD_STEAL, vcpu);
- if (single_task_running())
- vcpu_clear_wfx_traps(vcpu);
+ if (kvm_should_clear_wfx_trap(kvm_wfi_trap_policy))
+ vcpu_clear_wfi_trap(vcpu);
else
- vcpu_set_wfx_traps(vcpu);
+ vcpu_set_wfi_trap(vcpu);
+
+ if (kvm_should_clear_wfx_trap(kvm_wfe_trap_policy))
+ vcpu_clear_wfe_trap(vcpu);
+ else
+ vcpu_set_wfe_trap(vcpu);
if (vcpu_has_ptrauth(vcpu))
vcpu_ptrauth_disable(vcpu);
I find all of the layering rather hard to follow; we don't need
accessors for doing simple bit manipulation.
Rough sketch:
static bool kvm_vcpu_should_clear_twi(struct kvm_vcpu *vcpu)
{
if (unlikely(kvm_wfi_trap != KVM_WFX_DEFAULT))
return kvm_wfi_trap == KVM_WFX_NOTRAP;
return single_task_running() &&
(atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
vcpu->kvm->arch.vgic.nassgireq);
}
static bool kvm_vcpu_should_clear_twe(struct kvm_vcpu *vcpu)
{
if (unlikely(kvm_wfe_trap != KVM_WFX_DEFAULT))
return kvm_wfe_trap == KVM_WFX_NOTRAP;
return single_task_running();
}
static void kvm_vcpu_load_compute_hcr(struct kvm_vcpu *vcpu)
{
vcpu->arch.hcr_el2 |= HCR_TWE | HCR_TWI;
if (kvm_vcpu_should_clear_twe(vcpu))
vcpu->arch.hcr_el2 &= ~HCR_TWE;
if (kvm_vcpu_should_clear_twi(vcpu))
vcpu->arch.hcr_el2 &= ~HCR_TWI;
}
Will do.
And if we really wanted to, the non-default trap configuration could be
moved to vcpu_reset_hcr() if we cared.
Might as well.
