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qemu/hw/char/xen_console.c
David Woodhouse a72ccc7fc4 hw/xen: add support for Xen primary console in emulated mode 
The primary console is special because the toolstack maps a page into
the guest for its ring, and also allocates the guest-side event channel.
The guest's grant table is even primed to export that page using a known
grant ref#. Add support for all that in emulated mode, so that we can
have a primary console.

For reasons unclear, the backends running under real Xen don't just use
a mapping of the well-known GNTTAB_RESERVED_CONSOLE grant ref (which
would also be in the ring-ref node in XenStore). Instead, the toolstack
sets the ring-ref node of the primary console to the GFN of the guest
page. The backend is expected to handle that special case and map it
with foreignmem operations instead.

We don't have an implementation of foreignmem ops for emulated Xen mode,
so just make it map GNTTAB_RESERVED_CONSOLE instead. This would probably
work for real Xen too, but we can't work out how to make real Xen create
a primary console of type "ioemu" to make QEMU drive it, so we can't
test that; might as well leave it as it is for now under Xen.

Now at last we can boot the Xen PV shim and run PV kernels in QEMU.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
2023-11-07 08:54:20 +00:00

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/*
* Copyright (C) International Business Machines Corp., 2005
* Author(s): Anthony Liguori <aliguori@us.ibm.com>
*
* Copyright (C) Red Hat 2007
*
* Xen Console
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; under version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include "qemu/osdep.h"
#include "qemu/cutils.h"
#include <sys/select.h>
#include <termios.h>
#include "qapi/error.h"
#include "sysemu/sysemu.h"
#include "chardev/char-fe.h"
#include "hw/xen/xen-backend.h"
#include "hw/xen/xen-bus-helper.h"
#include "hw/qdev-properties.h"
#include "hw/qdev-properties-system.h"
#include "hw/xen/interface/io/console.h"
#include "hw/xen/interface/io/xs_wire.h"
#include "hw/xen/interface/grant_table.h"
#include "hw/i386/kvm/xen_primary_console.h"
#include "trace.h"
struct buffer {
uint8_t *data;
size_t consumed;
size_t size;
size_t capacity;
size_t max_capacity;
};
struct XenConsole {
struct XenDevice xendev; /* must be first */
XenEventChannel *event_channel;
int dev;
struct buffer buffer;
char *fe_path;
unsigned int ring_ref;
void *sring;
CharBackend chr;
int backlog;
};
typedef struct XenConsole XenConsole;
#define TYPE_XEN_CONSOLE_DEVICE "xen-console"
OBJECT_DECLARE_SIMPLE_TYPE(XenConsole, XEN_CONSOLE_DEVICE)
static bool buffer_append(XenConsole *con)
{
struct buffer *buffer = &con->buffer;
XENCONS_RING_IDX cons, prod, size;
struct xencons_interface *intf = con->sring;
cons = intf->out_cons;
prod = intf->out_prod;
xen_mb();
size = prod - cons;
if ((size == 0) || (size > sizeof(intf->out)))
return false;
if ((buffer->capacity - buffer->size) < size) {
buffer->capacity += (size + 1024);
buffer->data = g_realloc(buffer->data, buffer->capacity);
}
while (cons != prod)
buffer->data[buffer->size++] = intf->out[
MASK_XENCONS_IDX(cons++, intf->out)];
xen_mb();
intf->out_cons = cons;
xen_device_notify_event_channel(XEN_DEVICE(con), con->event_channel, NULL);
if (buffer->max_capacity &&
buffer->size > buffer->max_capacity) {
/* Discard the middle of the data. */
size_t over = buffer->size - buffer->max_capacity;
uint8_t *maxpos = buffer->data + buffer->max_capacity;
memmove(maxpos - over, maxpos, over);
buffer->data = g_realloc(buffer->data, buffer->max_capacity);
buffer->size = buffer->capacity = buffer->max_capacity;
if (buffer->consumed > buffer->max_capacity - over)
buffer->consumed = buffer->max_capacity - over;
}
return true;
}
static void buffer_advance(struct buffer *buffer, size_t len)
{
buffer->consumed += len;
if (buffer->consumed == buffer->size) {
buffer->consumed = 0;
buffer->size = 0;
}
}
static int ring_free_bytes(XenConsole *con)
{
struct xencons_interface *intf = con->sring;
XENCONS_RING_IDX cons, prod, space;
cons = intf->in_cons;
prod = intf->in_prod;
xen_mb();
space = prod - cons;
if (space > sizeof(intf->in))
return 0; /* ring is screwed: ignore it */
return (sizeof(intf->in) - space);
}
static int xencons_can_receive(void *opaque)
{
XenConsole *con = opaque;
return ring_free_bytes(con);
}
static void xencons_receive(void *opaque, const uint8_t *buf, int len)
{
XenConsole *con = opaque;
struct xencons_interface *intf = con->sring;
XENCONS_RING_IDX prod;
int i, max;
max = ring_free_bytes(con);
/* The can_receive() func limits this, but check again anyway */
if (max < len)
len = max;
prod = intf->in_prod;
for (i = 0; i < len; i++) {
intf->in[MASK_XENCONS_IDX(prod++, intf->in)] =
buf[i];
}
xen_wmb();
intf->in_prod = prod;
xen_device_notify_event_channel(XEN_DEVICE(con), con->event_channel, NULL);
}
static bool xencons_send(XenConsole *con)
{
ssize_t len, size;
size = con->buffer.size - con->buffer.consumed;
if (qemu_chr_fe_backend_connected(&con->chr)) {
len = qemu_chr_fe_write(&con->chr,
con->buffer.data + con->buffer.consumed,
size);
} else {
len = size;
}
if (len < 1) {
if (!con->backlog) {
con->backlog = 1;
}
} else {
buffer_advance(&con->buffer, len);
if (con->backlog && len == size) {
con->backlog = 0;
}
}
return len > 0;
}
/* -------------------------------------------------------------------- */
static bool con_event(void *_xendev)
{
XenConsole *con = XEN_CONSOLE_DEVICE(_xendev);
bool done_something;
if (xen_device_backend_get_state(&con->xendev) != XenbusStateConnected) {
return false;
}
done_something = buffer_append(con);
if (con->buffer.size - con->buffer.consumed) {
done_something |= xencons_send(con);
}
return done_something;
}
/* -------------------------------------------------------------------- */
static bool xen_console_connect(XenDevice *xendev, Error **errp)
{
XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
unsigned int port, limit;
if (xen_device_frontend_scanf(xendev, "ring-ref", "%u",
&con->ring_ref) != 1) {
error_setg(errp, "failed to read ring-ref");
return false;
}
if (xen_device_frontend_scanf(xendev, "port", "%u", &port) != 1) {
error_setg(errp, "failed to read remote port");
return false;
}
if (xen_device_frontend_scanf(xendev, "limit", "%u", &limit) == 1) {
con->buffer.max_capacity = limit;
}
con->event_channel = xen_device_bind_event_channel(xendev, port,
con_event,
con,
errp);
if (!con->event_channel) {
return false;
}
switch (con->dev) {
case 0:
/*
* The primary console is special. For real Xen the ring-ref is
* actually a GFN which needs to be mapped as foreignmem.
*/
if (xen_mode != XEN_EMULATE) {
xen_pfn_t mfn = (xen_pfn_t)con->ring_ref;
con->sring = qemu_xen_foreignmem_map(xendev->frontend_id, NULL,
PROT_READ | PROT_WRITE,
1, &mfn, NULL);
if (!con->sring) {
error_setg(errp, "failed to map console page");
return false;
}
break;
}
/*
* For Xen emulation, we still follow the convention of ring-ref
* holding the GFN, but we map the fixed GNTTAB_RESERVED_CONSOLE
* grant ref because there is no implementation of foreignmem
* operations for emulated mode. The emulation code which handles
* the guest-side page and event channel also needs to be informed
* of the backend event channel port, in order to reconnect to it
* after a soft reset.
*/
xen_primary_console_set_be_port(
xen_event_channel_get_local_port(con->event_channel));
con->ring_ref = GNTTAB_RESERVED_CONSOLE;
/* fallthrough */
default:
con->sring = xen_device_map_grant_refs(xendev,
&con->ring_ref, 1,
PROT_READ | PROT_WRITE,
errp);
if (!con->sring) {
error_prepend(errp, "failed to map console grant ref: ");
return false;
}
break;
}
trace_xen_console_connect(con->dev, con->ring_ref, port,
con->buffer.max_capacity);
qemu_chr_fe_set_handlers(&con->chr, xencons_can_receive,
xencons_receive, NULL, NULL, con, NULL,
true);
return true;
}
static void xen_console_disconnect(XenDevice *xendev, Error **errp)
{
XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
trace_xen_console_disconnect(con->dev);
qemu_chr_fe_set_handlers(&con->chr, NULL, NULL, NULL, NULL,
con, NULL, true);
if (con->event_channel) {
xen_device_unbind_event_channel(xendev, con->event_channel,
errp);
con->event_channel = NULL;
if (xen_mode == XEN_EMULATE && !con->dev) {
xen_primary_console_set_be_port(0);
}
}
if (con->sring) {
if (!con->dev && xen_mode != XEN_EMULATE) {
qemu_xen_foreignmem_unmap(con->sring, 1);
} else {
xen_device_unmap_grant_refs(xendev, con->sring,
&con->ring_ref, 1, errp);
}
con->sring = NULL;
}
}
static void xen_console_frontend_changed(XenDevice *xendev,
enum xenbus_state frontend_state,
Error **errp)
{
ERRP_GUARD();
enum xenbus_state backend_state = xen_device_backend_get_state(xendev);
switch (frontend_state) {
case XenbusStateInitialised:
case XenbusStateConnected:
if (backend_state == XenbusStateConnected) {
break;
}
xen_console_disconnect(xendev, errp);
if (*errp) {
break;
}
if (!xen_console_connect(xendev, errp)) {
xen_device_backend_set_state(xendev, XenbusStateClosing);
break;
}
xen_device_backend_set_state(xendev, XenbusStateConnected);
break;
case XenbusStateClosing:
xen_device_backend_set_state(xendev, XenbusStateClosing);
break;
case XenbusStateClosed:
case XenbusStateUnknown:
xen_console_disconnect(xendev, errp);
if (*errp) {
break;
}
xen_device_backend_set_state(xendev, XenbusStateClosed);
break;
default:
break;
}
}
static char *xen_console_get_name(XenDevice *xendev, Error **errp)
{
XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
if (con->dev == -1) {
XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
char fe_path[XENSTORE_ABS_PATH_MAX + 1];
int idx = (xen_mode == XEN_EMULATE) ? 0 : 1;
char *value;
/* Theoretically we could go up to INT_MAX here but that's overkill */
while (idx < 100) {
if (!idx) {
snprintf(fe_path, sizeof(fe_path),
"/local/domain/%u/console", xendev->frontend_id);
} else {
snprintf(fe_path, sizeof(fe_path),
"/local/domain/%u/device/console/%u",
xendev->frontend_id, idx);
}
value = qemu_xen_xs_read(xenbus->xsh, XBT_NULL, fe_path, NULL);
if (!value) {
if (errno == ENOENT) {
con->dev = idx;
goto found;
}
error_setg(errp, "cannot read %s: %s", fe_path,
strerror(errno));
return NULL;
}
free(value);
idx++;
}
error_setg(errp, "cannot find device index for console device");
return NULL;
}
found:
return g_strdup_printf("%u", con->dev);
}
static void xen_console_unrealize(XenDevice *xendev)
{
XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
trace_xen_console_unrealize(con->dev);
/* Disconnect from the frontend in case this has not already happened */
xen_console_disconnect(xendev, NULL);
qemu_chr_fe_deinit(&con->chr, false);
}
static void xen_console_realize(XenDevice *xendev, Error **errp)
{
ERRP_GUARD();
XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
Chardev *cs = qemu_chr_fe_get_driver(&con->chr);
unsigned int u;
if (!cs) {
error_setg(errp, "no backing character device");
return;
}
if (con->dev == -1) {
error_setg(errp, "no device index provided");
return;
}
/*
* The Xen primary console is special. The ring-ref is actually a GFN to
* be mapped directly as foreignmem (not a grant ref), and the guest port
* was allocated *for* the guest by the toolstack. The guest gets these
* through HVMOP_get_param and can use the console long before it's got
* XenStore up and running. We cannot create those for a true Xen guest,
* but we can for Xen emulation.
*/
if (!con->dev) {
if (xen_mode == XEN_EMULATE) {
xen_primary_console_create();
} else if (xen_device_frontend_scanf(xendev, "ring-ref", "%u", &u)
!= 1 ||
xen_device_frontend_scanf(xendev, "port", "%u", &u) != 1) {
error_setg(errp, "cannot create primary Xen console");
return;
}
}
trace_xen_console_realize(con->dev, object_get_typename(OBJECT(cs)));
if (CHARDEV_IS_PTY(cs)) {
/* Strip the leading 'pty:' */
xen_device_frontend_printf(xendev, "tty", "%s", cs->filename + 4);
}
/* No normal PV driver initialization for the primary console under Xen */
if (!con->dev && xen_mode != XEN_EMULATE) {
xen_console_connect(xendev, errp);
}
}
static char *console_frontend_path(struct qemu_xs_handle *xenstore,
unsigned int dom_id, unsigned int dev)
{
if (!dev) {
return g_strdup_printf("/local/domain/%u/console", dom_id);
} else {
return g_strdup_printf("/local/domain/%u/device/console/%u", dom_id,
dev);
}
}
static char *xen_console_get_frontend_path(XenDevice *xendev, Error **errp)
{
XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
char *ret = console_frontend_path(xenbus->xsh, xendev->frontend_id,
con->dev);
if (!ret) {
error_setg(errp, "failed to create frontend path");
}
return ret;
}
static Property xen_console_properties[] = {
DEFINE_PROP_CHR("chardev", XenConsole, chr),
DEFINE_PROP_INT32("idx", XenConsole, dev, -1),
DEFINE_PROP_END_OF_LIST(),
};
static void xen_console_class_init(ObjectClass *class, void *data)
{
DeviceClass *dev_class = DEVICE_CLASS(class);
XenDeviceClass *xendev_class = XEN_DEVICE_CLASS(class);
xendev_class->backend = "console";
xendev_class->device = "console";
xendev_class->get_name = xen_console_get_name;
xendev_class->realize = xen_console_realize;
xendev_class->frontend_changed = xen_console_frontend_changed;
xendev_class->unrealize = xen_console_unrealize;
xendev_class->get_frontend_path = xen_console_get_frontend_path;
device_class_set_props(dev_class, xen_console_properties);
}
static const TypeInfo xen_console_type_info = {
.name = TYPE_XEN_CONSOLE_DEVICE,
.parent = TYPE_XEN_DEVICE,
.instance_size = sizeof(XenConsole),
.class_init = xen_console_class_init,
};
static void xen_console_register_types(void)
{
type_register_static(&xen_console_type_info);
}
type_init(xen_console_register_types)
/* Called to instantiate a XenConsole when the backend is detected. */
static void xen_console_device_create(XenBackendInstance *backend,
QDict *opts, Error **errp)
{
ERRP_GUARD();
XenBus *xenbus = xen_backend_get_bus(backend);
const char *name = xen_backend_get_name(backend);
unsigned long number;
char *fe = NULL, *type = NULL, *output = NULL;
char label[32];
XenDevice *xendev = NULL;
XenConsole *con;
Chardev *cd = NULL;
struct qemu_xs_handle *xsh = xenbus->xsh;
if (qemu_strtoul(name, NULL, 10, &number) || number > INT_MAX) {
error_setg(errp, "failed to parse name '%s'", name);
goto fail;
}
trace_xen_console_device_create(number);
fe = console_frontend_path(xsh, xen_domid, number);
if (fe == NULL) {
error_setg(errp, "failed to generate frontend path");
goto fail;
}
if (xs_node_scanf(xsh, XBT_NULL, fe, "type", errp, "%ms", &type) != 1) {
error_prepend(errp, "failed to read console device type: ");
goto fail;
}
if (strcmp(type, "ioemu")) {
error_setg(errp, "declining to handle console type '%s'",
type);
goto fail;
}
xendev = XEN_DEVICE(qdev_new(TYPE_XEN_CONSOLE_DEVICE));
con = XEN_CONSOLE_DEVICE(xendev);
con->dev = number;
snprintf(label, sizeof(label), "xencons%ld", number);
if (xs_node_scanf(xsh, XBT_NULL, fe, "output", NULL, "%ms", &output) == 1) {
/*
* FIXME: sure we want to support implicit
* muxed monitors here?
*/
cd = qemu_chr_new_mux_mon(label, output, NULL);
if (!cd) {
error_setg(errp, "console: No valid chardev found at '%s': ",
output);
goto fail;
}
} else if (number) {
cd = serial_hd(number);
if (!cd) {
error_prepend(errp, "console: No serial device #%ld found: ",
number);
goto fail;
}
} else {
/* No 'output' node on primary console: use null. */
cd = qemu_chr_new(label, "null", NULL);
if (!cd) {
error_setg(errp, "console: failed to create null device");
goto fail;
}
}
if (!qemu_chr_fe_init(&con->chr, cd, errp)) {
error_prepend(errp, "console: failed to initialize backing chardev: ");
goto fail;
}
if (qdev_realize_and_unref(DEVICE(xendev), BUS(xenbus), errp)) {
xen_backend_set_device(backend, xendev);
goto done;
}
error_prepend(errp, "realization of console device %lu failed: ",
number);
fail:
if (xendev) {
object_unparent(OBJECT(xendev));
}
done:
g_free(fe);
free(type);
free(output);
}
static void xen_console_device_destroy(XenBackendInstance *backend,
Error **errp)
{
ERRP_GUARD();
XenDevice *xendev = xen_backend_get_device(backend);
XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
trace_xen_console_device_destroy(con->dev);
object_unparent(OBJECT(xendev));
}
static const XenBackendInfo xen_console_backend_info = {
.type = "console",
.create = xen_console_device_create,
.destroy = xen_console_device_destroy,
};
static void xen_console_register_backend(void)
{
xen_backend_register(&xen_console_backend_info);
}
xen_backend_init(xen_console_register_backend);
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