Re: [PATCH] target/arm: Report KVM's actual PSCI version to guest in dtb

[Akihiko Odaki]

Reviewed-by: Akihiko Odaki <akihiko.odaki@gmail.com>

On Thu, Feb 24, 2022 at 10:46 PM Peter Maydell <peter.maydell@linaro.org> wrote:
>
> When we're using KVM, the PSCI implementation is provided by the
> kernel, but QEMU has to tell the guest about it via the device tree.
> Currently we look at the KVM_CAP_ARM_PSCI_0_2 capability to determine
> if the kernel is providing at least PSCI 0.2, but if the kernel
> provides a newer version than that we will still only tell the guest
> it has PSCI 0.2.  (This is fairly harmless; it just means the guest
> won't use newer parts of the PSCI API.)
>
> The kernel exposes the specific PSCI version it is implementing via
> the ONE_REG API; use this to report in the dtb that the PSCI
> implementation is 1.0-compatible if appropriate.  (The device tree
> binding currently only distinguishes "pre-0.2", "0.2-compatible" and
> "1.0-compatible".)
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> Based-on: 20220213035753.34577-1-akihiko.odaki@gmail.com
> ("[PATCH v2] target/arm: Support PSCI 1.1 and SMCCC 1.0")
> though note that to compile on arm hosts you'll need the
> bugfix to that patch from which I describe in a reply to it.
>
>  target/arm/kvm-consts.h |  1 +
>  hw/arm/boot.c           |  5 ++---
>  target/arm/kvm64.c      | 12 ++++++++++++
>  3 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/target/arm/kvm-consts.h b/target/arm/kvm-consts.h
> index e770921ddc2..faacf96fdc7 100644
> --- a/target/arm/kvm-consts.h
> +++ b/target/arm/kvm-consts.h
> @@ -95,6 +95,7 @@ MISMATCH_CHECK(QEMU_PSCI_1_0_FN_PSCI_FEATURES, 
> PSCI_1_0_FN_PSCI_FEATURES);
>
>  #define QEMU_PSCI_VERSION_0_1                     0x00001
>  #define QEMU_PSCI_VERSION_0_2                     0x00002
> +#define QEMU_PSCI_VERSION_1_0                     0x10000
>  #define QEMU_PSCI_VERSION_1_1                     0x10001
>
>  MISMATCH_CHECK(QEMU_PSCI_0_2_RET_TOS_MIGRATION_NOT_REQUIRED, 
> PSCI_0_2_TOS_MP);
> diff --git a/hw/arm/boot.c b/hw/arm/boot.c
> index 0eeef94ceb5..a47f38dfc90 100644
> --- a/hw/arm/boot.c
> +++ b/hw/arm/boot.c
> @@ -488,9 +488,8 @@ static void fdt_add_psci_node(void *fdt)
>      }
>
>      qemu_fdt_add_subnode(fdt, "/psci");
> -    if (armcpu->psci_version == QEMU_PSCI_VERSION_0_2 ||
> -        armcpu->psci_version == QEMU_PSCI_VERSION_1_1) {
> -        if (armcpu->psci_version == QEMU_PSCI_VERSION_0_2) {
> +    if (armcpu->psci_version >= QEMU_PSCI_VERSION_0_2) {
> +        if (armcpu->psci_version < QEMU_PSCI_VERSION_1_0) {
>              const char comp[] = "arm,psci-0.2\0arm,psci";
>              qemu_fdt_setprop(fdt, "/psci", "compatible", comp, sizeof(comp));
>          } else {
> diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
> index 64d48bfb19d..ccadfbbe72b 100644
> --- a/target/arm/kvm64.c
> +++ b/target/arm/kvm64.c
> @@ -849,6 +849,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
>      uint64_t mpidr;
>      ARMCPU *cpu = ARM_CPU(cs);
>      CPUARMState *env = &cpu->env;
> +    uint64_t psciver;
>
>      if (cpu->kvm_target == QEMU_KVM_ARM_TARGET_NONE ||
>          !object_dynamic_cast(OBJECT(cpu), TYPE_AARCH64_CPU)) {
> @@ -904,6 +905,17 @@ int kvm_arch_init_vcpu(CPUState *cs)
>          }
>      }
>
> +    /*
> +     * KVM reports the exact PSCI version it is implementing via a
> +     * special sysreg. If it is present, use its contents to determine
> +     * what to report to the guest in the dtb (it is the PSCI version,
> +     * in the same 15-bits major 16-bits minor format that PSCI_VERSION
> +     * returns).
> +     */
> +    if (!kvm_get_one_reg(cs, KVM_REG_ARM_PSCI_VERSION, &psciver)) {
> +        cpu->psci_version = psciver;
> +    }
> +
>      /*
>       * When KVM is in use, PSCI is emulated in-kernel and not by qemu.
>       * Currently KVM has its own idea about MPIDR assignment, so we
> --
> 2.25.1
>