Re: [PATCH v3 11/20] KVM: arm/arm64: Move timer save/restore out of the hyp code

Marc Zyngier
2017-10-09T17:47:11Z

On 23/09/17 01:41, Christoffer Dall wrote:
> As we are about to be lazy with saving and restoring the timer
> registers, we prepare by moving all possible timer configuration logic
> out of the hyp code. All virtual timer registers can be programmed from
> EL1 and since the arch timer is always a level triggered interrupt we
> can safely do this with interrupts disabled in the host kernel on the
> way to the guest without taking vtimer interrupts in the host kernel
> (yet).
>
> The downside is that the cntvoff register can only be programmed from
> hyp mode, so we jump into hyp mode and back to program it. This is also
> safe, because the host kernel doesn't use the virtual timer in the KVM
> code. It may add a little performance performance penalty, but only
> until following commits where we move this operation to vcpu load/put.
>
> Signed-off-by: Christoffer Dall <cdall@linaro.org>
> ---
> arch/arm/include/asm/kvm_asm.h | 2 ++
> arch/arm/include/asm/kvm_hyp.h | 4 +--
> arch/arm/kvm/hyp/switch.c | 7 ++--
> arch/arm64/include/asm/kvm_asm.h | 2 ++
> arch/arm64/include/asm/kvm_hyp.h | 4 +--
> arch/arm64/kvm/hyp/switch.c | 6 ++--
> virt/kvm/arm/arch_timer.c | 40 ++++++++++++++++++++++
> virt/kvm/arm/hyp/timer-sr.c | 74 +++++++++++++++++-----------------------
> 8 files changed, 87 insertions(+), 52 deletions(-)
>
> diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h
> index 14d68a4..36dd296 100644
> --- a/arch/arm/include/asm/kvm_asm.h
> +++ b/arch/arm/include/asm/kvm_asm.h
> @@ -68,6 +68,8 @@ extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
> extern void __kvm_tlb_flush_vmid(struct kvm *kvm);
> extern void __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu);
>
> +extern void __kvm_timer_set_cntvoff(u32 cntvoff_low, u32 cntvoff_high);
> +
> extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
>
> extern void __init_stage2_translation(void);
> diff --git a/arch/arm/include/asm/kvm_hyp.h b/arch/arm/include/asm/kvm_hyp.h
> index 14b5903..ab20ffa 100644
> --- a/arch/arm/include/asm/kvm_hyp.h
> +++ b/arch/arm/include/asm/kvm_hyp.h
> @@ -98,8 +98,8 @@
> #define cntvoff_el2 CNTVOFF
> #define cnthctl_el2 CNTHCTL
>
> -void __timer_save_state(struct kvm_vcpu *vcpu);
> -void __timer_restore_state(struct kvm_vcpu *vcpu);
> +void __timer_enable_traps(struct kvm_vcpu *vcpu);
> +void __timer_disable_traps(struct kvm_vcpu *vcpu);
>
> void __vgic_v2_save_state(struct kvm_vcpu *vcpu);
> void __vgic_v2_restore_state(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm/kvm/hyp/switch.c b/arch/arm/kvm/hyp/switch.c
> index ebd2dd4..330c9ce 100644
> --- a/arch/arm/kvm/hyp/switch.c
> +++ b/arch/arm/kvm/hyp/switch.c
> @@ -174,7 +174,7 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> __activate_vm(vcpu);
>
> __vgic_restore_state(vcpu);
> - __timer_restore_state(vcpu);
> + __timer_enable_traps(vcpu);
>
> __sysreg_restore_state(guest_ctxt);
> __banked_restore_state(guest_ctxt);
> @@ -191,7 +191,8 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>
> __banked_save_state(guest_ctxt);
> __sysreg_save_state(guest_ctxt);
> - __timer_save_state(vcpu);
> + __timer_disable_traps(vcpu);
> +
> __vgic_save_state(vcpu);
>
> __deactivate_traps(vcpu);
> @@ -237,7 +238,7 @@ void __hyp_text __noreturn __hyp_panic(int cause)
>
> vcpu = (struct kvm_vcpu *)read_sysreg(HTPIDR);
> host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> - __timer_save_state(vcpu);
> + __timer_disable_traps(vcpu);
> __deactivate_traps(vcpu);
> __deactivate_vm(vcpu);
> __banked_restore_state(host_ctxt);
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 26a64d0..ab4d0a9 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -55,6 +55,8 @@ extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
> extern void __kvm_tlb_flush_vmid(struct kvm *kvm);
> extern void __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu);
>
> +extern void __kvm_timer_set_cntvoff(u32 cntvoff_low, u32 cntvoff_high);
> +
> extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
>
> extern u64 __vgic_v3_get_ich_vtr_el2(void);
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 4572a9b..08d3bb6 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -129,8 +129,8 @@ void __vgic_v3_save_state(struct kvm_vcpu *vcpu);
> void __vgic_v3_restore_state(struct kvm_vcpu *vcpu);
> int __vgic_v3_perform_cpuif_access(struct kvm_vcpu *vcpu);
>
> -void __timer_save_state(struct kvm_vcpu *vcpu);
> -void __timer_restore_state(struct kvm_vcpu *vcpu);
> +void __timer_enable_traps(struct kvm_vcpu *vcpu);
> +void __timer_disable_traps(struct kvm_vcpu *vcpu);
>
> void __sysreg_save_host_state(struct kvm_cpu_context *ctxt);
> void __sysreg_restore_host_state(struct kvm_cpu_context *ctxt);
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 945e79c..4994f4b 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -298,7 +298,7 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
> __activate_vm(vcpu);
>
> __vgic_restore_state(vcpu);
> - __timer_restore_state(vcpu);
> + __timer_enable_traps(vcpu);
>
> /*
> * We must restore the 32-bit state before the sysregs, thanks
> @@ -368,7 +368,7 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>
> __sysreg_save_guest_state(guest_ctxt);
> __sysreg32_save_state(vcpu);
> - __timer_save_state(vcpu);
> + __timer_disable_traps(vcpu);
> __vgic_save_state(vcpu);
>
> __deactivate_traps(vcpu);
> @@ -436,7 +436,7 @@ void __hyp_text __noreturn __hyp_panic(void)
>
> vcpu = (struct kvm_vcpu *)read_sysreg(tpidr_el2);
> host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
> - __timer_save_state(vcpu);
> + __timer_disable_traps(vcpu);
> __deactivate_traps(vcpu);
> __deactivate_vm(vcpu);
> __sysreg_restore_host_state(host_ctxt);
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index 7f87099..4254f88 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -276,6 +276,20 @@ static void phys_timer_emulate(struct kvm_vcpu *vcpu,
> soft_timer_start(&timer->phys_timer, kvm_timer_compute_delta(timer_ctx));
> }
>
> +static void timer_save_state(struct kvm_vcpu *vcpu)
> +{
> + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> +
> + if (timer->enabled) {
> + vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl);
> + vtimer->cnt_cval = read_sysreg_el0(cntv_cval);
> + }
> +
> + /* Disable the virtual timer */
> + write_sysreg_el0(0, cntv_ctl);
> +}
> +
> /*
> * Schedule the background timer before calling kvm_vcpu_block, so that this
> * thread is removed from its waitqueue and made runnable when there's a timer
> @@ -312,6 +326,18 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu)
> soft_timer_start(&timer->bg_timer, kvm_timer_earliest_exp(vcpu));
> }
>
> +static void timer_restore_state(struct kvm_vcpu *vcpu)
> +{
> + struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> +
> + if (timer->enabled) {
> + write_sysreg_el0(vtimer->cnt_cval, cntv_cval);
> + isb();
> + write_sysreg_el0(vtimer->cnt_ctl, cntv_ctl);
> + }
> +}
> +
> void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
> {
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> @@ -320,6 +346,13 @@ void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
> timer->armed = false;
> }
>
> +static void set_cntvoff(u64 cntvoff)
> +{
> + u32 low = cntvoff & GENMASK(31, 0);
> + u32 high = (cntvoff >> 32) & GENMASK(31, 0);

upper_32_bits/lower_32_bits?

> + kvm_call_hyp(__kvm_timer_set_cntvoff, low, high);

Maybe a comment as to why we need to split the 64bit value in two 32bit
words (32bit ARM PCS is getting in the way).

> +}
> +
> static void kvm_timer_flush_hwstate_vgic(struct kvm_vcpu *vcpu)
> {
> struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> @@ -423,6 +456,7 @@ static void kvm_timer_flush_hwstate_user(struct kvm_vcpu *vcpu)
> void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
> {
> struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> + struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
>
> if (unlikely(!timer->enabled))
> return;
> @@ -436,6 +470,9 @@ void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
> kvm_timer_flush_hwstate_user(vcpu);
> else
> kvm_timer_flush_hwstate_vgic(vcpu);
> +
> + set_cntvoff(vtimer->cntvoff);
> + timer_restore_state(vcpu);
> }
>
> /**
> @@ -455,6 +492,9 @@ void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu)
> */
> soft_timer_cancel(&timer->phys_timer, NULL);
>
> + timer_save_state(vcpu);
> + set_cntvoff(0);
> +
> /*
> * The guest could have modified the timer registers or the timer
> * could have expired, update the timer state.
> diff --git a/virt/kvm/arm/hyp/timer-sr.c b/virt/kvm/arm/hyp/timer-sr.c
> index 4734915..a6c3b10 100644
> --- a/virt/kvm/arm/hyp/timer-sr.c
> +++ b/virt/kvm/arm/hyp/timer-sr.c
> @@ -21,58 +21,48 @@
>
> #include <asm/kvm_hyp.h>
>
> -/* vcpu is already in the HYP VA space */
> -void __hyp_text __timer_save_state(struct kvm_vcpu *vcpu)
> +void __hyp_text __kvm_timer_set_cntvoff(u32 cntvoff_low, u32 cntvoff_high)
> +{
> + u64 cntvoff = (u64)cntvoff_high << 32 | cntvoff_low;
> + write_sysreg(cntvoff, cntvoff_el2);
> +}
> +
> +void __hyp_text enable_phys_timer(void)
> {
> - struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> - struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> u64 val;
>
> - if (timer->enabled) {
> - vtimer->cnt_ctl = read_sysreg_el0(cntv_ctl);
> - vtimer->cnt_cval = read_sysreg_el0(cntv_cval);
> - }
> + /* Allow physical timer/counter access for the host */
> + val = read_sysreg(cnthctl_el2);
> + val |= CNTHCTL_EL1PCTEN | CNTHCTL_EL1PCEN;
> + write_sysreg(val, cnthctl_el2);
> +}
>
> - /* Disable the virtual timer */
> - write_sysreg_el0(0, cntv_ctl);
> +void __hyp_text disable_phys_timer(void)
> +{
> + u64 val;
>
> /*
> + * Disallow physical timer access for the guest
> + * Physical counter access is allowed
> + */
> + val = read_sysreg(cnthctl_el2);
> + val &= ~CNTHCTL_EL1PCEN;
> + val |= CNTHCTL_EL1PCTEN;
> + write_sysreg(val, cnthctl_el2);
> +}
> +
> +void __hyp_text __timer_disable_traps(struct kvm_vcpu *vcpu)
> +{
> + /*
> * We don't need to do this for VHE since the host kernel runs in EL2
> * with HCR_EL2.TGE ==1, which makes those bits have no impact.
> */
> - if (!has_vhe()) {
> - /* Allow physical timer/counter access for the host */
> - val = read_sysreg(cnthctl_el2);
> - val |= CNTHCTL_EL1PCTEN | CNTHCTL_EL1PCEN;
> - write_sysreg(val, cnthctl_el2);
> - }
> -
> - /* Clear cntvoff for the host */
> - write_sysreg(0, cntvoff_el2);
> + if (!has_vhe())
> + enable_phys_timer();
> }
>
> -void __hyp_text __timer_restore_state(struct kvm_vcpu *vcpu)
> +void __hyp_text __timer_enable_traps(struct kvm_vcpu *vcpu)
> {
> - struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> - struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> - u64 val;
> -
> - /* Those bits are already configured at boot on VHE-system */
> - if (!has_vhe()) {
> - /*
> - * Disallow physical timer access for the guest
> - * Physical counter access is allowed
> - */
> - val = read_sysreg(cnthctl_el2);
> - val &= ~CNTHCTL_EL1PCEN;
> - val |= CNTHCTL_EL1PCTEN;
> - write_sysreg(val, cnthctl_el2);
> - }
> -
> - if (timer->enabled) {
> - write_sysreg(vtimer->cntvoff, cntvoff_el2);
> - write_sysreg_el0(vtimer->cnt_cval, cntv_cval);
> - isb();
> - write_sysreg_el0(vtimer->cnt_ctl, cntv_ctl);
> - }
> + if (!has_vhe())
> + disable_phys_timer();
> }
>

Otherwise:

Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>

M.
--
Jazz is not dead. It just smells funny...