[PATCH v6 19/21] KVM: arm64: Emulate physical counter offsetting on non-ECV systems
Marc Zyngier
maz at kernel.org
Tue Aug 10 04:27:48 PDT 2021
On Wed, 04 Aug 2021 09:58:17 +0100,
Oliver Upton <oupton at google.com> wrote:
>
> Unfortunately, ECV hasn't yet arrived in any tangible hardware. At the
> same time, controlling the guest view of the physical counter-timer is
> useful. Support guest counter-timer offsetting on non-ECV systems by
> trapping guest accesses to the physical counter-timer. Emulate reads of
> the physical counter in the fast exit path.
>
> Signed-off-by: Oliver Upton <oupton at google.com>
> ---
> arch/arm64/include/asm/sysreg.h | 1 +
> arch/arm64/kvm/arch_timer.c | 53 +++++++++++++++----------
> arch/arm64/kvm/hyp/include/hyp/switch.h | 29 ++++++++++++++
> arch/arm64/kvm/hyp/nvhe/timer-sr.c | 11 ++++-
> 4 files changed, 70 insertions(+), 24 deletions(-)
>
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index c34672aa65b9..e49790ae5da4 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -505,6 +505,7 @@
> #define SYS_AMEVCNTR0_MEM_STALL SYS_AMEVCNTR0_EL0(3)
>
> #define SYS_CNTFRQ_EL0 sys_reg(3, 3, 14, 0, 0)
> +#define SYS_CNTPCT_EL0 sys_reg(3, 3, 14, 0, 1)
>
> #define SYS_CNTP_TVAL_EL0 sys_reg(3, 3, 14, 2, 0)
> #define SYS_CNTP_CTL_EL0 sys_reg(3, 3, 14, 2, 1)
> diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> index 9ead94aa867d..b7cb63acf2a0 100644
> --- a/arch/arm64/kvm/arch_timer.c
> +++ b/arch/arm64/kvm/arch_timer.c
> @@ -51,7 +51,7 @@ static void kvm_arm_timer_write(struct kvm_vcpu *vcpu,
> static u64 kvm_arm_timer_read(struct kvm_vcpu *vcpu,
> struct arch_timer_context *timer,
> enum kvm_arch_timer_regs treg);
> -static void kvm_timer_enable_traps_vhe(void);
> +static void kvm_timer_enable_traps_vhe(struct kvm_vcpu *vcpu);
>
> u32 timer_get_ctl(struct arch_timer_context *ctxt)
> {
> @@ -175,6 +175,12 @@ static void timer_set_guest_offset(struct arch_timer_context *ctxt, u64 offset)
> }
> }
>
> +static bool ptimer_emulation_required(struct kvm_vcpu *vcpu)
> +{
> + return timer_get_offset(vcpu_ptimer(vcpu)) &&
> + !cpus_have_const_cap(ARM64_ECV);
What Andrew said! :-)
> +}
> +
> u64 kvm_phys_timer_read(void)
> {
> return timecounter->cc->read(timecounter->cc);
> @@ -184,8 +190,13 @@ static void get_timer_map(struct kvm_vcpu *vcpu, struct timer_map *map)
> {
> if (has_vhe()) {
> map->direct_vtimer = vcpu_vtimer(vcpu);
> - map->direct_ptimer = vcpu_ptimer(vcpu);
> - map->emul_ptimer = NULL;
> + if (!ptimer_emulation_required(vcpu)) {
> + map->direct_ptimer = vcpu_ptimer(vcpu);
> + map->emul_ptimer = NULL;
> + } else {
> + map->direct_ptimer = NULL;
> + map->emul_ptimer = vcpu_ptimer(vcpu);
> + }
> } else {
> map->direct_vtimer = vcpu_vtimer(vcpu);
> map->direct_ptimer = NULL;
> @@ -671,7 +682,7 @@ void kvm_timer_vcpu_load(struct kvm_vcpu *vcpu)
> timer_emulate(map.emul_ptimer);
>
> if (has_vhe())
> - kvm_timer_enable_traps_vhe();
> + kvm_timer_enable_traps_vhe(vcpu);
> }
>
> bool kvm_timer_should_notify_user(struct kvm_vcpu *vcpu)
> @@ -1392,22 +1403,29 @@ int kvm_timer_enable(struct kvm_vcpu *vcpu)
> * The host kernel runs at EL2 with HCR_EL2.TGE == 1,
> * and this makes those bits have no effect for the host kernel execution.
> */
> -static void kvm_timer_enable_traps_vhe(void)
> +static void kvm_timer_enable_traps_vhe(struct kvm_vcpu *vcpu)
> {
> /* When HCR_EL2.E2H ==1, EL1PCEN and EL1PCTEN are shifted by 10 */
> u32 cnthctl_shift = 10;
> - u64 val;
> + u64 val, mask;
> +
> + mask = CNTHCTL_EL1PCEN << cnthctl_shift;
> + mask |= CNTHCTL_EL1PCTEN << cnthctl_shift;
>
> - /*
> - * VHE systems allow the guest direct access to the EL1 physical
> - * timer/counter.
> - */
> val = read_sysreg(cnthctl_el2);
> - val |= (CNTHCTL_EL1PCEN << cnthctl_shift);
> - val |= (CNTHCTL_EL1PCTEN << cnthctl_shift);
>
> if (cpus_have_const_cap(ARM64_ECV))
> val |= CNTHCTL_ECV;
> +
> + /*
> + * VHE systems allow the guest direct access to the EL1 physical
> + * timer/counter if offsetting isn't requested on a non-ECV system.
> + */
> + if (ptimer_emulation_required(vcpu))
> + val &= ~mask;
> + else
> + val |= mask;
> +
> write_sysreg(val, cnthctl_el2);
> }
>
> @@ -1462,9 +1480,6 @@ static int kvm_arm_timer_set_attr_offset(struct kvm_vcpu *vcpu,
> u64 __user *uaddr = (u64 __user *)(long)attr->addr;
> u64 offset;
>
> - if (!cpus_have_const_cap(ARM64_ECV))
> - return -ENXIO;
> -
> if (get_user(offset, uaddr))
> return -EFAULT;
>
> @@ -1513,9 +1528,6 @@ static int kvm_arm_timer_get_attr_offset(struct kvm_vcpu *vcpu,
> u64 __user *uaddr = (u64 __user *)(long)attr->addr;
> u64 offset;
>
> - if (!cpus_have_const_cap(ARM64_ECV))
> - return -ENXIO;
> -
> offset = timer_get_offset(vcpu_ptimer(vcpu));
> return put_user(offset, uaddr);
> }
> @@ -1539,11 +1551,8 @@ int kvm_arm_timer_has_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
> switch (attr->attr) {
> case KVM_ARM_VCPU_TIMER_IRQ_VTIMER:
> case KVM_ARM_VCPU_TIMER_IRQ_PTIMER:
> - return 0;
> case KVM_ARM_VCPU_TIMER_OFFSET:
> - if (cpus_have_const_cap(ARM64_ECV))
> - return 0;
> - break;
> + return 0;
> }
>
> return -ENXIO;
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index e4a2f295a394..abd3813a709e 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -15,6 +15,7 @@
> #include <linux/jump_label.h>
> #include <uapi/linux/psci.h>
>
> +#include <kvm/arm_arch_timer.h>
> #include <kvm/arm_psci.h>
>
> #include <asm/barrier.h>
> @@ -405,6 +406,31 @@ static inline bool __hyp_handle_ptrauth(struct kvm_vcpu *vcpu)
> return true;
> }
>
> +static inline u64 __timer_read_cntpct(struct kvm_vcpu *vcpu)
> +{
> + return __arch_counter_get_cntpct() - vcpu_ptimer(vcpu)->host_offset;
> +}
> +
> +static inline bool __hyp_handle_counter(struct kvm_vcpu *vcpu)
> +{
> + u32 sysreg;
> + int rt;
> + u64 rv;
You could start with a
if (cpus_have_final_cap(ARM64_ECV))
return false;
which will speed-up the exit on ECV-capable systems.
> +
> + if (kvm_vcpu_trap_get_class(vcpu) != ESR_ELx_EC_SYS64)
> + return false;
> +
> + sysreg = esr_sys64_to_sysreg(kvm_vcpu_get_esr(vcpu));
> + if (sysreg != SYS_CNTPCT_EL0)
> + return false;
You also want to check for CNTPCTSS_EL0 which will also be caught by
this trap.
> +
> + rt = kvm_vcpu_sys_get_rt(vcpu);
> + rv = __timer_read_cntpct(vcpu);
> + vcpu_set_reg(vcpu, rt, rv);
> + __kvm_skip_instr(vcpu);
> + return true;
> +}
> +
> /*
> * Return true when we were able to fixup the guest exit and should return to
> * the guest, false when we should restore the host state and return to the
> @@ -439,6 +465,9 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> if (*exit_code != ARM_EXCEPTION_TRAP)
> goto exit;
>
> + if (__hyp_handle_counter(vcpu))
> + goto guest;
> +
> if (cpus_have_final_cap(ARM64_WORKAROUND_CAVIUM_TX2_219_TVM) &&
> kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_SYS64 &&
> handle_tx2_tvm(vcpu))
> diff --git a/arch/arm64/kvm/hyp/nvhe/timer-sr.c b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
> index 5b8b4cd02506..67236c2e0ba7 100644
> --- a/arch/arm64/kvm/hyp/nvhe/timer-sr.c
> +++ b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
> @@ -44,10 +44,17 @@ void __timer_enable_traps(struct kvm_vcpu *vcpu)
>
> /*
> * Disallow physical timer access for the guest
> - * Physical counter access is allowed
> */
> val = read_sysreg(cnthctl_el2);
> val &= ~CNTHCTL_EL1PCEN;
> - val |= CNTHCTL_EL1PCTEN;
> +
> + /*
> + * Disallow physical counter access for the guest if offsetting is
> + * requested on a non-ECV system.
> + */
> + if (vcpu_ptimer(vcpu)->host_offset && !cpus_have_const_cap(ARM64_ECV))
> + val &= ~CNTHCTL_EL1PCTEN;
> + else
> + val |= CNTHCTL_EL1PCTEN;
> write_sysreg(val, cnthctl_el2);
> }
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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