diff mbox series

[v6] KVM: arm64: Add early_param to control WFx trapping

Message ID 20240523174056.1565133-1-coltonlewis@google.com (mailing list archive)
State New
Headers show
Series [v6] KVM: arm64: Add early_param to control WFx trapping | expand

Commit Message

Colton Lewis May 23, 2024, 5:40 p.m. UTC 
Add an early_params to control WFI and WFE trapping. This is to
control the degree guests can wait for interrupts on their own without
being trapped by KVM. Options for each param are trap and notrap. trap
enables the trap. notrap disables the trap. Note that when enabled,
traps are allowed but not guaranteed by the CPU architecture. Absent
an explicitly set policy, default to current behavior: disabling the
trap if only a single task is running and enabling otherwise.

Signed-off-by: Colton Lewis <coltonlewis@google.com>
---
v6:
 * Rebase to v6.9.1
 * Move decision to enable WFx traps back to vcpu load time
 * Move policy enum to arm.c and mark variable as __read_mostly
 * Add explicit disclaimer traps are not guaranteed even when setting enabled
 * Remove explicit "default" case from early param handling as it is not needed

v5:
https://lore.kernel.org/kvmarm/20240430181444.670773-1-coltonlewis@google.com/

v4:
https://lore.kernel.org/kvmarm/20240422181716.237284-1-coltonlewis@google.com/

v3:
https://lore.kernel.org/kvmarm/20240410175437.793508-1-coltonlewis@google.com/

v2:
https://lore.kernel.org/kvmarm/20240319164341.1674863-1-coltonlewis@google.com/

v1:
https://lore.kernel.org/kvmarm/20240129213918.3124494-1-coltonlewis@google.com/

 .../admin-guide/kernel-parameters.txt         | 18 +++++
 arch/arm64/include/asm/kvm_emulate.h          | 16 -----
 arch/arm64/kvm/arm.c                          | 68 ++++++++++++++++++-
 3 files changed, 83 insertions(+), 19 deletions(-)

--
2.45.1.288.g0e0cd299f1-goog

Comments

Jing Zhang June 14, 2024, 4:25 p.m. UTC | #1 
Hi Colton,

On Thu, May 23, 2024 at 10:41 AM Colton Lewis <coltonlewis@google.com> wrote:
>
> Add an early_params to control WFI and WFE trapping. This is to
> control the degree guests can wait for interrupts on their own without
> being trapped by KVM. Options for each param are trap and notrap. trap
> enables the trap. notrap disables the trap. Note that when enabled,
> traps are allowed but not guaranteed by the CPU architecture. Absent
> an explicitly set policy, default to current behavior: disabling the
> trap if only a single task is running and enabling otherwise.
>
> Signed-off-by: Colton Lewis <coltonlewis@google.com>
> ---
> v6:
>  * Rebase to v6.9.1
>  * Move decision to enable WFx traps back to vcpu load time
>  * Move policy enum to arm.c and mark variable as __read_mostly
>  * Add explicit disclaimer traps are not guaranteed even when setting enabled
>  * Remove explicit "default" case from early param handling as it is not needed
>
> v5:
> https://lore.kernel.org/kvmarm/20240430181444.670773-1-coltonlewis@google.com/
>
> v4:
> https://lore.kernel.org/kvmarm/20240422181716.237284-1-coltonlewis@google.com/
>
> v3:
> https://lore.kernel.org/kvmarm/20240410175437.793508-1-coltonlewis@google.com/
>
> v2:
> https://lore.kernel.org/kvmarm/20240319164341.1674863-1-coltonlewis@google.com/
>
> v1:
> https://lore.kernel.org/kvmarm/20240129213918.3124494-1-coltonlewis@google.com/
>
>  .../admin-guide/kernel-parameters.txt         | 18 +++++
>  arch/arm64/include/asm/kvm_emulate.h          | 16 -----
>  arch/arm64/kvm/arm.c                          | 68 ++++++++++++++++++-
>  3 files changed, 83 insertions(+), 19 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 396137ee018d..f334265a9cfa 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2693,6 +2693,24 @@
>                         [KVM,ARM,EARLY] Allow use of GICv4 for direct
>                         injection of LPIs.
>
> +       kvm-arm.wfe_trap_policy=
> +                       [KVM,ARM] Control when to set WFE instruction trap for
> +                       KVM VMs. Traps are allowed but not guaranteed by the
> +                       CPU architecture.
> +
> +                       trap: set WFE instruction trap
> +
> +                       notrap: clear WFE instruction trap
> +
> +       kvm-arm.wfi_trap_policy=
> +                       [KVM,ARM] Control when to set WFI instruction trap for
> +                       KVM VMs. Traps are allowed but not guaranteed by the
> +                       CPU architecture.
> +
> +                       trap: set WFI instruction trap
> +
> +                       notrap: clear WFI instruction trap
> +
>         kvm_cma_resv_ratio=n [PPC,EARLY]
>                         Reserves given percentage from system memory area for
>                         contiguous memory allocation for KVM hash pagetable
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 975af30af31f..68c4a170b871 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -109,22 +109,6 @@ static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
>         return (unsigned long *)&vcpu->arch.hcr_el2;
>  }
>
> -static inline void vcpu_clear_wfx_traps(struct kvm_vcpu *vcpu)
> -{
> -       vcpu->arch.hcr_el2 &= ~HCR_TWE;
> -       if (atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
> -           vcpu->kvm->arch.vgic.nassgireq)
> -               vcpu->arch.hcr_el2 &= ~HCR_TWI;
> -       else
> -               vcpu->arch.hcr_el2 |= HCR_TWI;
> -}
> -
> -static inline void vcpu_set_wfx_traps(struct kvm_vcpu *vcpu)
> -{
> -       vcpu->arch.hcr_el2 |= HCR_TWE;
> -       vcpu->arch.hcr_el2 |= HCR_TWI;
> -}
> -
>  static inline void vcpu_ptrauth_enable(struct kvm_vcpu *vcpu)
>  {
>         vcpu->arch.hcr_el2 |= (HCR_API | HCR_APK);
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index c4a0a35e02c7..1cd58ca5d410 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -47,6 +47,15 @@
>
>  static enum kvm_mode kvm_mode = KVM_MODE_DEFAULT;
>
> +enum kvm_wfx_trap_policy {
> +       KVM_WFX_NOTRAP_SINGLE_TASK, /* Default option */
> +       KVM_WFX_NOTRAP,
> +       KVM_WFX_TRAP,
> +};
> +
> +static enum kvm_wfx_trap_policy kvm_wfi_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
> +static enum kvm_wfx_trap_policy kvm_wfe_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
> +
>  DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
>
>  DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
> @@ -428,6 +437,24 @@ void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
>
>  }
>
> +static bool kvm_vcpu_should_clear_twi(struct kvm_vcpu *vcpu)
> +{
> +       if (likely(kvm_wfi_trap_policy == KVM_WFX_NOTRAP_SINGLE_TASK))
> +               return single_task_running() &&
> +                       (atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
> +                        vcpu->kvm->arch.vgic.nassgireq);
> +
> +       return kvm_wfi_trap_policy == KVM_WFX_NOTRAP;
> +}
> +
> +static bool kvm_vcpu_should_clear_twe(struct kvm_vcpu *vcpu)
> +{
> +       if (likely(kvm_wfe_trap_policy == KVM_WFX_NOTRAP_SINGLE_TASK))
> +               return single_task_running();
> +
> +       return kvm_wfe_trap_policy == KVM_WFX_NOTRAP;
> +}
> +
>  void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>  {
>         struct kvm_s2_mmu *mmu;
> @@ -461,10 +488,15 @@ 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_vcpu_should_clear_twe(vcpu))
> +               vcpu->arch.hcr_el2 &= ~HCR_TWE;
> +       else
> +               vcpu->arch.hcr_el2 |= HCR_TWE;
> +
> +       if (kvm_vcpu_should_clear_twi(vcpu))
> +               vcpu->arch.hcr_el2 &= ~HCR_TWI;
>         else
> -               vcpu_set_wfx_traps(vcpu);
> +               vcpu->arch.hcr_el2 |= HCR_TWI;
>
>         if (vcpu_has_ptrauth(vcpu))
>                 vcpu_ptrauth_disable(vcpu);
> @@ -2663,6 +2695,36 @@ static int __init early_kvm_mode_cfg(char *arg)
>  }
>  early_param("kvm-arm.mode", early_kvm_mode_cfg);
>
> +static int __init early_kvm_wfx_trap_policy_cfg(char *arg, enum kvm_wfx_trap_policy *p)
> +{
> +       if (!arg)
> +               return -EINVAL;
> +
> +       if (strcmp(arg, "trap") == 0) {
> +               *p = KVM_WFX_TRAP;
> +               return 0;
> +       }
> +
> +       if (strcmp(arg, "notrap") == 0) {
> +               *p = KVM_WFX_NOTRAP;
> +               return 0;
> +       }
> +
> +       return -EINVAL;
> +}
> +
> +static int __init early_kvm_wfi_trap_policy_cfg(char *arg)
> +{
> +       return early_kvm_wfx_trap_policy_cfg(arg, &kvm_wfi_trap_policy);
> +}
> +early_param("kvm-arm.wfi_trap_policy", early_kvm_wfi_trap_policy_cfg);
> +
> +static int __init early_kvm_wfe_trap_policy_cfg(char *arg)
> +{
> +       return early_kvm_wfx_trap_policy_cfg(arg, &kvm_wfe_trap_policy);
> +}
> +early_param("kvm-arm.wfe_trap_policy", early_kvm_wfe_trap_policy_cfg);
> +
>  enum kvm_mode kvm_get_mode(void)
>  {
>         return kvm_mode;
> --
> 2.45.1.288.g0e0cd299f1-goog
>

Reviewed-by: Jing Zhang <jingzhangos@google.com>

Jing
Oliver Upton June 14, 2024, 7:09 p.m. UTC | #2 
On Thu, May 23, 2024 at 05:40:55PM +0000, Colton Lewis wrote:
> Add an early_params to control WFI and WFE trapping. This is to
> control the degree guests can wait for interrupts on their own without
> being trapped by KVM. Options for each param are trap and notrap. trap
> enables the trap. notrap disables the trap. Note that when enabled,
> traps are allowed but not guaranteed by the CPU architecture. Absent
> an explicitly set policy, default to current behavior: disabling the
> trap if only a single task is running and enabling otherwise.
> 
> Signed-off-by: Colton Lewis <coltonlewis@google.com>
> ---
> v6:
>  * Rebase to v6.9.1

As in from the stable tree? Please base your patches on an -rc tag, and
especially one from this release cycle.

> +static bool kvm_vcpu_should_clear_twi(struct kvm_vcpu *vcpu)
> +{
> +	if (likely(kvm_wfi_trap_policy == KVM_WFX_NOTRAP_SINGLE_TASK))
> +		return single_task_running() &&
> +			(atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
> +			 vcpu->kvm->arch.vgic.nassgireq);
> +
> +	return kvm_wfi_trap_policy == KVM_WFX_NOTRAP;
> +}

Generally, it is more readable to organize your code in such a way that
multiline statements are unnested as much as possible. So if you were to
invert the if condition it'd become a bit cleaner.

Here is what I plan on squashing into this patch,
kvm_vcpu_should_clear_twe() got the same treatment for the sake of
consistency.

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 9cddd1096b0a..53e23528d2cf 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -557,20 +557,20 @@ static void vcpu_set_pauth_traps(struct kvm_vcpu *vcpu)
 
 static bool kvm_vcpu_should_clear_twi(struct kvm_vcpu *vcpu)
 {
-	if (likely(kvm_wfi_trap_policy == KVM_WFX_NOTRAP_SINGLE_TASK))
-		return single_task_running() &&
-			(atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
-			 vcpu->kvm->arch.vgic.nassgireq);
+	if (unlikely(kvm_wfi_trap_policy != KVM_WFX_NOTRAP_SINGLE_TASK))
+		return kvm_wfi_trap_policy == KVM_WFX_NOTRAP;
 
-	return kvm_wfi_trap_policy == 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 (likely(kvm_wfe_trap_policy == KVM_WFX_NOTRAP_SINGLE_TASK))
-		return single_task_running();
+	if (unlikely(kvm_wfe_trap_policy != KVM_WFX_NOTRAP_SINGLE_TASK))
+		return kvm_wfe_trap_policy == KVM_WFX_NOTRAP;
 
-	return kvm_wfe_trap_policy == KVM_WFX_NOTRAP;
+	return single_task_running();
 }
 
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
Oliver Upton June 14, 2024, 8:12 p.m. UTC | #3 
On Thu, 23 May 2024 17:40:55 +0000, Colton Lewis wrote:
> Add an early_params to control WFI and WFE trapping. This is to
> control the degree guests can wait for interrupts on their own without
> being trapped by KVM. Options for each param are trap and notrap. trap
> enables the trap. notrap disables the trap. Note that when enabled,
> traps are allowed but not guaranteed by the CPU architecture. Absent
> an explicitly set policy, default to current behavior: disabling the
> trap if only a single task is running and enabling otherwise.
> 
> [...]

Applied to kvmarm/next, thanks!

[1/1] KVM: arm64: Add early_param to control WFx trapping
      https://git.kernel.org/kvmarm/kvmarm/c/0b5afe05377d

--
Best,
Oliver
diff mbox series

Patch

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 396137ee018d..f334265a9cfa 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2693,6 +2693,24 @@ 
 			[KVM,ARM,EARLY] Allow use of GICv4 for direct
 			injection of LPIs.

+	kvm-arm.wfe_trap_policy=
+			[KVM,ARM] Control when to set WFE instruction trap for
+			KVM VMs. Traps are allowed but not guaranteed by the
+			CPU architecture.
+
+			trap: set WFE instruction trap
+
+			notrap: clear WFE instruction trap
+
+	kvm-arm.wfi_trap_policy=
+			[KVM,ARM] Control when to set WFI instruction trap for
+			KVM VMs. Traps are allowed but not guaranteed by the
+			CPU architecture.
+
+			trap: set WFI instruction trap
+
+			notrap: clear WFI instruction trap
+
 	kvm_cma_resv_ratio=n [PPC,EARLY]
 			Reserves given percentage from system memory area for
 			contiguous memory allocation for KVM hash pagetable
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index 975af30af31f..68c4a170b871 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -109,22 +109,6 @@  static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
 	return (unsigned long *)&vcpu->arch.hcr_el2;
 }

-static inline void vcpu_clear_wfx_traps(struct kvm_vcpu *vcpu)
-{
-	vcpu->arch.hcr_el2 &= ~HCR_TWE;
-	if (atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
-	    vcpu->kvm->arch.vgic.nassgireq)
-		vcpu->arch.hcr_el2 &= ~HCR_TWI;
-	else
-		vcpu->arch.hcr_el2 |= HCR_TWI;
-}
-
-static inline void vcpu_set_wfx_traps(struct kvm_vcpu *vcpu)
-{
-	vcpu->arch.hcr_el2 |= HCR_TWE;
-	vcpu->arch.hcr_el2 |= HCR_TWI;
-}
-
 static inline void vcpu_ptrauth_enable(struct kvm_vcpu *vcpu)
 {
 	vcpu->arch.hcr_el2 |= (HCR_API | HCR_APK);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index c4a0a35e02c7..1cd58ca5d410 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -47,6 +47,15 @@ 

 static enum kvm_mode kvm_mode = KVM_MODE_DEFAULT;

+enum kvm_wfx_trap_policy {
+	KVM_WFX_NOTRAP_SINGLE_TASK, /* Default option */
+	KVM_WFX_NOTRAP,
+	KVM_WFX_TRAP,
+};
+
+static enum kvm_wfx_trap_policy kvm_wfi_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
+static enum kvm_wfx_trap_policy kvm_wfe_trap_policy __read_mostly = KVM_WFX_NOTRAP_SINGLE_TASK;
+
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);

 DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
@@ -428,6 +437,24 @@  void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)

 }

+static bool kvm_vcpu_should_clear_twi(struct kvm_vcpu *vcpu)
+{
+	if (likely(kvm_wfi_trap_policy == KVM_WFX_NOTRAP_SINGLE_TASK))
+		return single_task_running() &&
+			(atomic_read(&vcpu->arch.vgic_cpu.vgic_v3.its_vpe.vlpi_count) ||
+			 vcpu->kvm->arch.vgic.nassgireq);
+
+	return kvm_wfi_trap_policy == KVM_WFX_NOTRAP;
+}
+
+static bool kvm_vcpu_should_clear_twe(struct kvm_vcpu *vcpu)
+{
+	if (likely(kvm_wfe_trap_policy == KVM_WFX_NOTRAP_SINGLE_TASK))
+		return single_task_running();
+
+	return kvm_wfe_trap_policy == KVM_WFX_NOTRAP;
+}
+
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	struct kvm_s2_mmu *mmu;
@@ -461,10 +488,15 @@  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_vcpu_should_clear_twe(vcpu))
+		vcpu->arch.hcr_el2 &= ~HCR_TWE;
+	else
+		vcpu->arch.hcr_el2 |= HCR_TWE;
+
+	if (kvm_vcpu_should_clear_twi(vcpu))
+		vcpu->arch.hcr_el2 &= ~HCR_TWI;
 	else
-		vcpu_set_wfx_traps(vcpu);
+		vcpu->arch.hcr_el2 |= HCR_TWI;

 	if (vcpu_has_ptrauth(vcpu))
 		vcpu_ptrauth_disable(vcpu);
@@ -2663,6 +2695,36 @@  static int __init early_kvm_mode_cfg(char *arg)
 }
 early_param("kvm-arm.mode", early_kvm_mode_cfg);

+static int __init early_kvm_wfx_trap_policy_cfg(char *arg, enum kvm_wfx_trap_policy *p)
+{
+	if (!arg)
+		return -EINVAL;
+
+	if (strcmp(arg, "trap") == 0) {
+		*p = KVM_WFX_TRAP;
+		return 0;
+	}
+
+	if (strcmp(arg, "notrap") == 0) {
+		*p = KVM_WFX_NOTRAP;
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
+static int __init early_kvm_wfi_trap_policy_cfg(char *arg)
+{
+	return early_kvm_wfx_trap_policy_cfg(arg, &kvm_wfi_trap_policy);
+}
+early_param("kvm-arm.wfi_trap_policy", early_kvm_wfi_trap_policy_cfg);
+
+static int __init early_kvm_wfe_trap_policy_cfg(char *arg)
+{
+	return early_kvm_wfx_trap_policy_cfg(arg, &kvm_wfe_trap_policy);
+}
+early_param("kvm-arm.wfe_trap_policy", early_kvm_wfe_trap_policy_cfg);
+
 enum kvm_mode kvm_get_mode(void)
 {
 	return kvm_mode;