/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2019 Conrad Meyer <cem@FreeBSD.org>.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * VM Generation Counter driver
 *
 * See, e.g., the "Virtual Machine Generation ID" white paper:
 * https://go.microsoft.com/fwlink/p/?LinkID=260709 , and perhaps also:
 * https://docs.microsoft.com/en-us/windows/win32/hyperv_v2/virtual-machine-generation-identifier ,
 * https://azure.microsoft.com/en-us/blog/accessing-and-using-azure-vm-unique-id/
 *
 * Microsoft introduced the concept in 2013 or so and seems to have
 * successfully driven it to a consensus standard among hypervisors, not just
 * HyperV/Azure:
 * - QEMU: https://bugzilla.redhat.com/show_bug.cgi?id=1118834
 * - VMware/ESXi: https://kb.vmware.com/s/article/2032586
 * - Xen: https://github.com/xenserver/xen-4.5/blob/master/tools/firmware/hvmloader/acpi/dsdt.asl#L456
 */

#include <sys/param.h>
#include <sys/bus.h>
#include <sys/eventhandler.h>
#include <sys/kernel.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/mutex.h>
#include <sys/random.h>
#include <sys/sysctl.h>
#include <sys/systm.h>

#include <contrib/dev/acpica/include/acpi.h>

#include <dev/acpica/acpivar.h>
#include <dev/random/randomdev.h>
#include <dev/random/random_harvestq.h>
#include <dev/vmgenc/vmgenc_acpi.h>

#ifndef ACPI_NOTIFY_STATUS_CHANGED
#define ACPI_NOTIFY_STATUS_CHANGED      0x80
#endif

#define GUID_BYTES      16

static const char *vmgenc_ids[] = {
        "VM_GEN_COUNTER",
        NULL
};
#if 0
MODULE_PNP_INFO("Z:_CID", acpi, vmgenc, vmgenc_ids, nitems(vmgenc_ids) - 1);
#endif

struct vmgenc_softc {
        volatile void   *vmg_pguid;
        uint8_t         vmg_cache_guid[GUID_BYTES];
};

static void
vmgenc_harvest_all(const void *p, size_t sz)
{
        size_t nbytes;

        while (sz > 0) {
                nbytes = MIN(sz,
                    sizeof(((struct harvest_event *)0)->he_entropy));
                random_harvest_direct(p, nbytes, RANDOM_PURE_VMGENID);
                p = (const char *)p + nbytes;
                sz -= nbytes;
        }
}

static void
vmgenc_status_changed(void *context)
{
        uint8_t guid[GUID_BYTES];
        struct vmgenc_softc *sc;
        device_t dev;

        dev = context;
        sc = device_get_softc(dev);

        /* Check for spurious notify events. */
        memcpy(guid, __DEVOLATILE(void *, sc->vmg_pguid), sizeof(guid));
        if (memcmp(guid, sc->vmg_cache_guid, GUID_BYTES) == 0)
                return; /* No change. */

        /* Update cache. */
        memcpy(sc->vmg_cache_guid, guid, GUID_BYTES);

        vmgenc_harvest_all(sc->vmg_cache_guid, sizeof(sc->vmg_cache_guid));

        EVENTHANDLER_INVOKE(acpi_vmgenc_event);
        acpi_UserNotify("VMGenerationCounter", acpi_get_handle(dev), 0);
}

static void
vmgenc_notify(ACPI_HANDLE h, UINT32 notify, void *context)
{
        device_t dev;

        dev = context;
        switch (notify) {
        case ACPI_NOTIFY_STATUS_CHANGED:
                /*
                 * We're possibly in GPE / interrupt context, kick the event up
                 * to a taskqueue.
                 */
                AcpiOsExecute(OSL_NOTIFY_HANDLER, vmgenc_status_changed, dev);
                break;
        default:
                device_printf(dev, "unknown notify %#x\n", notify);
                break;
        }
}

static int
vmgenc_probe(device_t dev)
{
        int rv;

        if (acpi_disabled("vmgenc"))
                return (ENXIO);
        rv = ACPI_ID_PROBE(device_get_parent(dev), dev,
            __DECONST(char **, vmgenc_ids), NULL);
        if (rv <= 0)
                device_set_desc(dev, "VM Generation Counter");
        return (rv);
}

static const char *
vmgenc_acpi_getname(ACPI_HANDLE handle, char data[static 256])
{
    ACPI_BUFFER buf;

    buf.Length = 256;
    buf.Pointer = data;

    if (ACPI_SUCCESS(AcpiGetName(handle, ACPI_FULL_PATHNAME, &buf)))
        return (data);
    return ("(unknown)");
}

static int
acpi_GetPackedUINT64(device_t dev, ACPI_HANDLE handle, char *path,
    uint64_t *out)
{
        char hpath[256];
        ACPI_STATUS status;
        ACPI_BUFFER buf;
        ACPI_OBJECT param[3];

        buf.Pointer = param;
        buf.Length = sizeof(param);
        status = AcpiEvaluateObject(handle, path, NULL, &buf);
        if (!ACPI_SUCCESS(status)) {
                device_printf(dev, "%s(%s::%s()): %s\n", __func__,
                    vmgenc_acpi_getname(handle, hpath), path,
                    AcpiFormatException(status));
                return (ENXIO);
        }
        if (param[0].Type != ACPI_TYPE_PACKAGE) {
                device_printf(dev, "%s(%s::%s()): Wrong type %#x\n", __func__,
                    vmgenc_acpi_getname(handle, hpath), path,
                    param[0].Type);
                return (ENXIO);
        }
        if (param[0].Package.Count != 2) {
                device_printf(dev, "%s(%s::%s()): Wrong number of results %u\n",
                    __func__, vmgenc_acpi_getname(handle, hpath), path,
                    param[0].Package.Count);
                return (ENXIO);
        }
        if (param[0].Package.Elements[0].Type != ACPI_TYPE_INTEGER ||
            param[0].Package.Elements[1].Type != ACPI_TYPE_INTEGER) {
                device_printf(dev, "%s(%s::%s()): Wrong type results %#x, %#x\n",
                    __func__, vmgenc_acpi_getname(handle, hpath), path,
                    param[0].Package.Elements[0].Type,
                    param[0].Package.Elements[1].Type);
                return (ENXIO);
        }

        *out = (param[0].Package.Elements[0].Integer.Value & UINT32_MAX) |
            ((uint64_t)param[0].Package.Elements[1].Integer.Value << 32);
        if (*out == 0)
                return (ENXIO);
        return (0);

}

static const struct random_source random_vmgenid = {
        .rs_ident = "VM Generation ID",
        .rs_source = RANDOM_PURE_VMGENID,
};

static int
vmgenc_attach(device_t dev)
{
        struct vmgenc_softc *sc;
        uint64_t guid_physaddr;
        ACPI_HANDLE h;
        int error;

        h = acpi_get_handle(dev);
        sc = device_get_softc(dev);

        error = acpi_GetPackedUINT64(dev, h, "ADDR", &guid_physaddr);
        if (error != 0)
                return (error);

        SYSCTL_ADD_OPAQUE(device_get_sysctl_ctx(dev),
            SYSCTL_CHILDREN(device_get_sysctl_tree(dev)), OID_AUTO, "guid",
            CTLFLAG_RD, sc->vmg_cache_guid, GUID_BYTES, "",
            "latest cached VM generation counter (128-bit UUID)");

        sc->vmg_pguid = AcpiOsMapMemory(guid_physaddr, GUID_BYTES);
        memcpy(sc->vmg_cache_guid, __DEVOLATILE(void *, sc->vmg_pguid),
            sizeof(sc->vmg_cache_guid));

        random_source_register(&random_vmgenid);
        vmgenc_harvest_all(sc->vmg_cache_guid, sizeof(sc->vmg_cache_guid));

        AcpiInstallNotifyHandler(h, ACPI_DEVICE_NOTIFY, vmgenc_notify, dev);
        return (0);
}

static device_method_t vmgenc_methods[] = {
        DEVMETHOD(device_probe,         vmgenc_probe),
        DEVMETHOD(device_attach,        vmgenc_attach),
        DEVMETHOD_END
};

static driver_t vmgenc_driver = {
        "vmgenc",
        vmgenc_methods,
        sizeof(struct vmgenc_softc),
};

DRIVER_MODULE(vmgenc, acpi, vmgenc_driver, NULL, NULL);
MODULE_DEPEND(vmgenc, acpi, 1, 1, 1);
MODULE_DEPEND(vmgenc, random_harvestq, 1, 1, 1);