[PATCH v1 1/3] KVM: arm64: Add ESR class to the hyp_enter hyp event

[Fuad Tabba]

Hi Vincent,

On Fri, 09 Oct 2026 09:45:27 +0100, Vincent Donnefort
<vdonnefort at google.com> wrote:

[...]
> To distinguish between a trap from host and from guest, add a "from="
> field, which has 3 possibilities: "host", "vcpu" or "firmware". This
> value can be deducted based on the existing vcpu field.

nit: "deduced". Also, "firmware" comes from the reason rather than
from the vcpu field.

[...]
> diff --git a/arch/arm64/include/asm/kvm_hypevents.h b/arch/arm64/include/asm/kvm_hypevents.h

[...]
> @@ -10,15 +10,10 @@
>  #ifndef __HYP_ENTER_EXIT_REASON
>  #define __HYP_ENTER_EXIT_REASON
>  enum hyp_enter_exit_reason {
> -        HYP_REASON_SMC,
> -        HYP_REASON_HVC,
> -        HYP_REASON_SYS,
> +        HYP_REASON_SMC = ESR_ELx_EC_MAX + 1,

This header now uses ESR_ELx_EC_MAX, so it should include <asm/esr.h>
rather than rely on its includers.

>          HYP_REASON_PSCI,
> -        HYP_REASON_HOST_ABORT,
> -        HYP_REASON_GUEST_EXIT,
> -        HYP_REASON_ERET_HOST,
> -        HYP_REASON_ERET_GUEST,
> -        HYP_REASON_UNKNOWN        /* Must be last */
> +        HYP_REASON_IRQ,
> +        HYP_REASON_ERET,
>  };

Aren't fixed trace points ABI? This changes the raw values of the
reason field (1 was hvc and is now WFx) and the strings it prints.
Keeping the old values and recording the EC in a new field would avoid
that.

[...]
> diff --git a/arch/arm64/kvm/hyp/nvhe/psci-relay.c b/arch/arm64/kvm/hyp/nvhe/psci-relay.c
[...]
> @@ -213,7 +213,7 @@ static void __noreturn __kvm_host_psci_cpu_entry(unsigned long pc, unsigned long
>          write_sysreg_el1(INIT_SCTLR_EL1_MMU_OFF, SYS_SCTLR);
>          write_sysreg(INIT_PSTATE_EL1, SPSR_EL2);
>
> -        trace_hyp_exit(host_ctxt, HYP_REASON_PSCI);
> +        trace_hyp_exit(host_ctxt, HYP_REASON_ERET);
>          __host_enter(host_ctxt);

This also replaces the PSCI, ERET_HOST and ERET_GUEST exit reasons
with a single ERET, which the commit message doesn't mention.

[...]
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c

[...]
> @@ -324,13 +324,15 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>          __debug_switch_to_guest(vcpu);
>
>          do {
> -                trace_hyp_exit(host_ctxt, HYP_REASON_ERET_GUEST);
> +                trace_hyp_exit(host_ctxt, HYP_REASON_ERET);
>
>                  /* Jump in the fire! */
>                  exit_code = __guest_enter(vcpu);
>
>                  /* And we're baaack! */
> -                trace_hyp_enter(host_ctxt, HYP_REASON_GUEST_EXIT);
> +                trace_hyp_enter(host_ctxt,
> +                                ARM_EXCEPTION_CODE(exit_code) == ARM_EXCEPTION_IRQ ?
> +                                HYP_REASON_IRQ : ESR_ELx_EC(read_sysreg_el2(SYS_ESR)));
>          } while (fixup_guest_exit(vcpu, &exit_code));

Could ESR_EL2 be read only when the event is enabled? The read happens
even when tracing is disabled or compiled out, so every non-IRQ guest
exit now does an extra one: with NVHE_EL2_DEBUG=n, __kvm_vcpu_run()
goes from two reads of ESR_EL2 to three.

[...]
> diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
[...]
>  static const char *__hyp_enter_exit_reason_str(u8 reason)
>  {
[...]
> +        if (reason <= ESR_ELx_EC_MAX) {
> +                int i;
> +
> +                for (i = 0; i < ARRAY_SIZE(class); i++) {
> +                        if (class[i].mask == reason)
> +                                return class[i].name;
> +                }
> +
> +                return "UNKNOWN_ESR";
> +        }

Could this print the EC value when it isn't in the table?
kvm_arm_exception_class has no entry for ILL, BTI, SME or GCS among
others, so an ARM_EXCEPTION_IL exit (EC 0x0E) shows up as UNKNOWN_ESR.

Cheers,
/fuad