Re: [RFC PATCH v5 51/52] hw/xen: Add xen_xenstore device for xenstore emulation

[David Woodhouse]

On 4 January 2023 12:01:54 GMT, "Dr. David Alan Gilbert" <dgilbert@redhat.com> 
wrote:
>* David Woodhouse (dwmw2@infradead.org) wrote:
>> From: David Woodhouse <dwmw@amazon.co.uk>
>> 
>> The hookup to event channel is a bit of a special case hack right now; as
>> we make this work for real PV driver back ends, that will be implemented
>> for the general case of Dom0 ports binding to DomU.
>> 
>> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
>> ---
>>  hw/i386/kvm/meson.build    |   1 +
>>  hw/i386/kvm/xen_evtchn.c   |   1 +
>>  hw/i386/kvm/xen_xenstore.c | 248 +++++++++++++++++++++++++++++++++++++
>>  hw/i386/kvm/xen_xenstore.h |  20 +++
>>  hw/i386/pc.c               |   2 +
>>  target/i386/kvm/xen-emu.c  |  12 ++
>>  6 files changed, 284 insertions(+)
>>  create mode 100644 hw/i386/kvm/xen_xenstore.c
>>  create mode 100644 hw/i386/kvm/xen_xenstore.h
>> 
>> diff --git a/hw/i386/kvm/meson.build b/hw/i386/kvm/meson.build
>> index e02449e4d4..6d6981fced 100644
>> --- a/hw/i386/kvm/meson.build
>> +++ b/hw/i386/kvm/meson.build
>> @@ -8,6 +8,7 @@ i386_kvm_ss.add(when: 'CONFIG_XEN_EMU', if_true: files(
>>    'xen_overlay.c',
>>    'xen_evtchn.c',
>>    'xen_gnttab.c',
>> +  'xen_xenstore.c',
>>    ))
>>  
>>  i386_ss.add_all(when: 'CONFIG_KVM', if_true: i386_kvm_ss)
>> diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c
>> index c0f6ef9dff..0653cad3bb 100644
>> --- a/hw/i386/kvm/xen_evtchn.c
>> +++ b/hw/i386/kvm/xen_evtchn.c
>> @@ -31,6 +31,7 @@
>>  
>>  #include "xen_evtchn.h"
>>  #include "xen_overlay.h"
>> +#include "xen_xenstore.h"
>>  
>>  #include "sysemu/kvm.h"
>>  #include "sysemu/kvm_xen.h"
>> diff --git a/hw/i386/kvm/xen_xenstore.c b/hw/i386/kvm/xen_xenstore.c
>> new file mode 100644
>> index 0000000000..63530059fa
>> --- /dev/null
>> +++ b/hw/i386/kvm/xen_xenstore.c
>> @@ -0,0 +1,248 @@
>> +/*
>> + * QEMU Xen emulation: Shared/overlay pages support
>> + *
>> + * Copyright © 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
>> + *
>> + * Authors: David Woodhouse <dwmw2@infradead.org>
>> + *
>> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
>> + * See the COPYING file in the top-level directory.
>> + */
>> +
>> +#include "qemu/osdep.h"
>> +
>> +#include "qemu/host-utils.h"
>> +#include "qemu/module.h"
>> +#include "qemu/main-loop.h"
>> +#include "qemu/cutils.h"
>> +#include "qapi/error.h"
>> +#include "qom/object.h"
>> +#include "migration/vmstate.h"
>> +
>> +#include "hw/sysbus.h"
>> +#include "hw/xen/xen.h"
>> +#include "xen_overlay.h"
>> +#include "xen_evtchn.h"
>> +#include "xen_xenstore.h"
>> +
>> +#include "sysemu/kvm.h"
>> +#include "sysemu/kvm_xen.h"
>> +
>> +#include "standard-headers/xen/io/xs_wire.h"
>> +#include "standard-headers/xen/event_channel.h"
>> +
>> +#define TYPE_XEN_XENSTORE "xen-xenstore"
>> +OBJECT_DECLARE_SIMPLE_TYPE(XenXenstoreState, XEN_XENSTORE)
>> +
>> +#define XEN_PAGE_SHIFT 12
>> +#define XEN_PAGE_SIZE (1ULL << XEN_PAGE_SHIFT)
>> +
>> +#define ENTRIES_PER_FRAME_V1 (XEN_PAGE_SIZE / sizeof(grant_entry_v1_t))
>> +#define ENTRIES_PER_FRAME_V2 (XEN_PAGE_SIZE / sizeof(grant_entry_v2_t))
>> +
>> +#define XENSTORE_HEADER_SIZE ((unsigned int)sizeof(struct xsd_sockmsg))
>> +
>> +struct XenXenstoreState {
>> +    /*< private >*/
>> +    SysBusDevice busdev;
>> +    /*< public >*/
>> +
>> +    MemoryRegion xenstore_page;
>> +    struct xenstore_domain_interface *xs;
>> +    uint8_t req_data[XENSTORE_HEADER_SIZE + XENSTORE_PAYLOAD_MAX];
>> +    uint8_t rsp_data[XENSTORE_HEADER_SIZE + XENSTORE_PAYLOAD_MAX];
>> +    uint32_t req_offset;
>> +    uint32_t rsp_offset;
>> +    bool rsp_pending;
>> +    bool fatal_error;
>> +
>> +    evtchn_port_t guest_port;
>> +    evtchn_port_t be_port;
>> +    struct xenevtchn_handle *eh;
>> +};
>> +
>> +struct XenXenstoreState *xen_xenstore_singleton;
>> +
>> +static void xen_xenstore_event(void *opaque);
>> +
>> +static void xen_xenstore_realize(DeviceState *dev, Error **errp)
>> +{
>> +    XenXenstoreState *s = XEN_XENSTORE(dev);
>> +
>> +    if (xen_mode != XEN_EMULATE) {
>> +        error_setg(errp, "Xen xenstore support is for Xen emulation");
>> +        return;
>> +    }
>> +    memory_region_init_ram(&s->xenstore_page, OBJECT(dev), 
>> "xen:xenstore_page",
>> +                           XEN_PAGE_SIZE, &error_abort);
>> +    memory_region_set_enabled(&s->xenstore_page, true);
>> +    s->xs = memory_region_get_ram_ptr(&s->xenstore_page);
>> +    memset(s->xs, 0, XEN_PAGE_SIZE);
>> +
>> +    /* We can't map it this early as KVM isn't ready */
>> +    xen_xenstore_singleton = s;
>> +
>> +    s->eh = xen_be_evtchn_open(NULL, 0);
>> +    if (!s->eh) {
>> +        error_setg(errp, "Xenstore evtchn port init failed");
>> +        return;
>> +    }
>> +    aio_set_fd_handler(qemu_get_aio_context(), xen_be_evtchn_fd(s->eh), 
>> true,
>> +                       xen_xenstore_event, NULL, NULL, NULL, s);
>> +}
>> +
>> +static bool xen_xenstore_is_needed(void *opaque)
>> +{
>> +    return xen_mode == XEN_EMULATE;
>> +}
>> +
>> +static int xen_xenstore_pre_save(void *opaque)
>> +{
>> +    XenXenstoreState *s = opaque;
>> +
>> +    if (s->eh) {
>> +        s->guest_port = xen_be_evtchn_get_guest_port(s->eh);
>> +    }
>> +    return 0;
>> +}
>> +
>> +static int xen_xenstore_post_load(void *opaque, int ver)
>> +{
>> +    XenXenstoreState *s = opaque;
>> +
>> +    /*
>> +     * As qemu/dom0, rebind to the guest's port. The Windows drivers may
>> +     * unbind the XenStore evtchn and rebind to it, having obtained the
>> +     * "remote" port through EVTCHNOP_status. In the case that migration
>> +     * occurs while it's unbound, the "remote" port needs to be the same
>> +     * as before so that the guest can find it, but should remain unbound.
>> +     */
>> +    if (s->guest_port) {
>> +        int be_port = xen_be_evtchn_bind_interdomain(s->eh, xen_domid, 
>> s->guest_port);
>> +        if (be_port < 0) {
>> +            return be_port;
>> +        }
>> +        s->be_port = be_port;
>> +    }
>> +    return 0;
>> +}
>> +
>> +static const VMStateDescription xen_xenstore_vmstate = {
>> +    .name = "xen_xenstore",
>> +    .version_id = 1,
>> +    .minimum_version_id = 1,
>> +    .needed = xen_xenstore_is_needed,
>> +    .pre_save = xen_xenstore_pre_save,
>> +    .post_load = xen_xenstore_post_load,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_UINT8_ARRAY(req_data, XenXenstoreState, 
>> sizeof_field(XenXenstoreState, req_data)),
>> +        VMSTATE_UINT8_ARRAY(rsp_data, XenXenstoreState, 
>> sizeof_field(XenXenstoreState, rsp_data)),
>> +        VMSTATE_UINT32(req_offset, XenXenstoreState),
>> +        VMSTATE_UINT32(rsp_offset, XenXenstoreState),
>> +        VMSTATE_BOOL(rsp_pending, XenXenstoreState),
>> +        VMSTATE_UINT32(guest_port, XenXenstoreState),
>> +        VMSTATE_BOOL(fatal_error, XenXenstoreState),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +
>> +static void xen_xenstore_class_init(ObjectClass *klass, void *data)
>> +{
>> +    DeviceClass *dc = DEVICE_CLASS(klass);
>> +
>> +    dc->realize = xen_xenstore_realize;
>> +    dc->vmsd = &xen_xenstore_vmstate;
>> +}
>> +
>> +static const TypeInfo xen_xenstore_info = {
>> +    .name          = TYPE_XEN_XENSTORE,
>> +    .parent        = TYPE_SYS_BUS_DEVICE,
>> +    .instance_size = sizeof(XenXenstoreState),
>> +    .class_init    = xen_xenstore_class_init,
>> +};
>> +
>> +void xen_xenstore_create(void)
>> +{
>> +    xen_xenstore_singleton = 
>> XEN_XENSTORE(sysbus_create_simple(TYPE_XEN_XENSTORE,
>> +                                                           -1, NULL));
>> +
>> +    /*
>> +     * Defer the init (xen_xenstore_reset()) until KVM is set up and the
>> +     * overlay page can be mapped.
>> +     */
>> +}
>> +
>> +static void xen_xenstore_register_types(void)
>> +{
>> +    type_register_static(&xen_xenstore_info);
>> +}
>> +
>> +type_init(xen_xenstore_register_types)
>> +
>> +uint16_t xen_xenstore_get_port(void)
>> +{
>> +    XenXenstoreState *s = xen_xenstore_singleton;
>> +    if (!s) {
>> +        return 0;
>> +    }
>> +    return s->guest_port;
>> +}
>> +
>> +static void xen_xenstore_event(void *opaque)
>> +{
>> +    XenXenstoreState *s = opaque;
>> +    evtchn_port_t port = xen_be_evtchn_pending(s->eh);
>> +    if (port != s->be_port) {
>> +        return;
>> +    }
>> +    printf("xenstore event\n");
>> +    /* We know this is a no-op. */
>> +    xen_be_evtchn_unmask(s->eh, port);
>> +    qemu_hexdump(stdout, "", s->xs, sizeof(*s->xs));
>
>debug ?

Perhaps, but it goes away in the next patch anyway, and Paul is working on 
something that actually works (instead of just returning ENOSYS to everything).