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Date:   Mon, 24 Aug 2020 20:33:59 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Michael Kelley <mikelley@...rosoft.com>
Cc:     Will Deacon <will@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        gregkh <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-hyperv@...r.kernel.org,
        linux-efi <linux-efi@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>, wei.liu@...nel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v7 07/10] arm64: hyperv: Initialize hypervisor on boot

On Mon, Aug 24, 2020 at 6:48 PM Michael Kelley <mikelley@...rosoft.com> wrote:
>
>  /*
> + * This function is invoked via the ACPI clocksource probe mechanism. We
> + * don't actually use any values from the ACPI GTDT table, but we set up
> + * the Hyper-V synthetic clocksource and do other initialization for
> + * interacting with Hyper-V the first time.  Using early_initcall to invoke
> + * this function is too late because interrupts are already enabled at that
> + * point, and hv_init_clocksource() must run before interrupts are enabled.
> + *
> + * 1. Setup the guest ID.
> + * 2. Get features and hints info from Hyper-V
> + * 3. Setup per-cpu VP indices.
> + * 4. Initialize the Hyper-V clocksource.
> + */
> +
> +static int __init hyperv_init(struct acpi_table_header *table)
> +{
> +       struct hv_get_vp_registers_output result;
> +       u32     a, b, c, d;
> +       u64     guest_id;
> +       int     i, cpuhp;
> +
> +       /*
> +        * If we're in a VM on Hyper-V, the ACPI hypervisor_id field will
> +        * have the string "MsHyperV".
> +        */
> +       if (strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8))
> +               return -EINVAL;
> +
> +       /* Setup the guest ID */
> +       guest_id = generate_guest_id(0, LINUX_VERSION_CODE, 0);
> +       hv_set_vpreg(HV_REGISTER_GUEST_OSID, guest_id);
> +
> +       /* Get the features and hints from Hyper-V */
> +       hv_get_vpreg_128(HV_REGISTER_FEATURES, &result);
> +       ms_hyperv.features = result.as32.a;
> +       ms_hyperv.misc_features = result.as32.c;
> +
> +       hv_get_vpreg_128(HV_REGISTER_ENLIGHTENMENTS, &result);
> +       ms_hyperv.hints = result.as32.a;
> +
> +       pr_info("Hyper-V: Features 0x%x, hints 0x%x, misc 0x%x\n",
> +               ms_hyperv.features, ms_hyperv.hints, ms_hyperv.misc_features);
> +
> +       /*
> +        * If Hyper-V has crash notifications, set crash_kexec_post_notifiers
> +        * so that we will report the panic to Hyper-V before running kdump.
> +        */
> +       if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE)
> +               crash_kexec_post_notifiers = true;
> +
> +       /* Get information about the Hyper-V host version */
> +       hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION, &result);
> +       a = result.as32.a;
> +       b = result.as32.b;
> +       c = result.as32.c;
> +       d = result.as32.d;
> +       pr_info("Hyper-V: Host Build %d.%d.%d.%d-%d-%d\n",
> +               b >> 16, b & 0xFFFF, a, d & 0xFFFFFF, c, d >> 24);
> +
> +       /* Allocate and initialize percpu VP index array */
> +       hv_vp_index = kmalloc_array(num_possible_cpus(), sizeof(*hv_vp_index),
> +                                   GFP_KERNEL);
> +       if (!hv_vp_index)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < num_possible_cpus(); i++)
> +               hv_vp_index[i] = VP_INVAL;
> +
> +       cpuhp = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
> +                       "arm64/hyperv_init:online", hv_cpu_init, NULL);
> +       if (cpuhp < 0)
> +               goto free_vp_index;
> +
> +       hv_init_clocksource();
> +       if (hv_stimer_alloc())
> +               goto remove_cpuhp_state;
> +
> +       hyperv_initialized = true;
> +       return 0;
> +
> +remove_cpuhp_state:
> +       cpuhp_remove_state(cpuhp);
> +free_vp_index:
> +       kfree(hv_vp_index);
> +       hv_vp_index = NULL;
> +       return -EINVAL;
> +}
> +TIMER_ACPI_DECLARE(hyperv, ACPI_SIG_GTDT, hyperv_init);

I think this has come up before, and I still don't consider it an acceptable
hack to hook platform initialization code into the timer code.

Please split out the timer into a standalone driver in drivers/clocksource
that can get reviewed by the clocksource maintainers.

      Arnd

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