Re: [PATCH v8 15/19] hvf: arm: Implement -cpu host

[Peter Maydell]

On Wed, 19 May 2021 at 21:23, Alexander Graf <agraf@csgraf.de> wrote:
>
> Now that we have working system register sync, we push more target CPU
> properties into the virtual machine. That might be useful in some
> situations, but is not the typical case that users want.
>
> So let's add a -cpu host option that allows them to explicitly pass all
> CPU capabilities of their host CPU into the guest.
>
> Signed-off-by: Alexander Graf <agraf@csgraf.de>
> Acked-by: Roman Bolshakov <r.bolshakov@yadro.com>
>
> ---
>
> v6 -> v7:
>
>   - Move function define to own header
>   - Do not propagate SVE features for HVF
>   - Remove stray whitespace change
>   - Verify that EL0 and EL1 do not allow AArch32 mode
>   - Only probe host CPU features once

> +static void hvf_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
> +{
> +    ARMISARegisters host_isar;

Can you zero-initialize this (with "= { }"), please? That way we
know we have zeroes in the aarch32 ID fields rather than random junk later...

> +    const struct isar_regs {
> +        int reg;
> +        uint64_t *val;
> +    } regs[] = {
> +        { HV_SYS_REG_ID_AA64PFR0_EL1, &host_isar.id_aa64pfr0 },
> +        { HV_SYS_REG_ID_AA64PFR1_EL1, &host_isar.id_aa64pfr1 },
> +        { HV_SYS_REG_ID_AA64DFR0_EL1, &host_isar.id_aa64dfr0 },
> +        { HV_SYS_REG_ID_AA64DFR1_EL1, &host_isar.id_aa64dfr1 },
> +        { HV_SYS_REG_ID_AA64ISAR0_EL1, &host_isar.id_aa64isar0 },
> +        { HV_SYS_REG_ID_AA64ISAR1_EL1, &host_isar.id_aa64isar1 },
> +        { HV_SYS_REG_ID_AA64MMFR0_EL1, &host_isar.id_aa64mmfr0 },
> +        { HV_SYS_REG_ID_AA64MMFR1_EL1, &host_isar.id_aa64mmfr1 },
> +        { HV_SYS_REG_ID_AA64MMFR2_EL1, &host_isar.id_aa64mmfr2 },
> +    };
> +    hv_vcpu_t fd;
> +    hv_vcpu_exit_t *exit;
> +    int i;
> +
> +    ahcf->dtb_compatible = "arm,arm-v8";
> +    ahcf->features = (1ULL << ARM_FEATURE_V8) |
> +                     (1ULL << ARM_FEATURE_NEON) |
> +                     (1ULL << ARM_FEATURE_AARCH64) |
> +                     (1ULL << ARM_FEATURE_PMU) |
> +                     (1ULL << ARM_FEATURE_GENERIC_TIMER);
> +
> +    /* We set up a small vcpu to extract host registers */
> +
> +    assert_hvf_ok(hv_vcpu_create(&fd, &exit, NULL));
> +    for (i = 0; i < ARRAY_SIZE(regs); i++) {
> +        assert_hvf_ok(hv_vcpu_get_sys_reg(fd, regs[i].reg, regs[i].val));
> +    }
> +    assert_hvf_ok(hv_vcpu_get_sys_reg(fd, HV_SYS_REG_MIDR_EL1, &ahcf->midr));
> +    assert_hvf_ok(hv_vcpu_destroy(fd));
> +
> +    ahcf->isar = host_isar;
> +    ahcf->reset_sctlr = 0x00c50078;

Why this value in particular? Could we just ask the scratch HVF CPU
for the value of SCTLR_EL1 rather than hardcoding something?

> +
> +    /* Make sure we don't advertise AArch32 support for EL0/EL1 */
> +    g_assert((host_isar.id_aa64pfr0 & 0xff) == 0x11);

This shouldn't really be an assert, I think. error_report() something
and return false, and then arm_cpu_realizefn() will fail, which should
cause us to exit.

> +}
> +
> +void hvf_arm_set_cpu_features_from_host(ARMCPU *cpu)
> +{
> +    if (!arm_host_cpu_features.dtb_compatible) {
> +        if (!hvf_enabled()) {
> +            cpu->host_cpu_probe_failed = true;
> +            return;
> +        }
> +        hvf_arm_get_host_cpu_features(&arm_host_cpu_features);
> +    }
> +
> +    cpu->dtb_compatible = arm_host_cpu_features.dtb_compatible;
> +    cpu->isar = arm_host_cpu_features.isar;
> +    cpu->env.features = arm_host_cpu_features.features;
> +    cpu->midr = arm_host_cpu_features.midr;
> +    cpu->reset_sctlr = arm_host_cpu_features.reset_sctlr;
> +}
> +
>  void hvf_arch_vcpu_destroy(CPUState *cpu)
>  {
>  }

thanks
-- PMM