[PATCH v3 09/28] hw/xen: Clean up event channel 'type_val' handling to use union

David Woodhouse
2023-10-25T14:51:27Z

From: David Woodhouse <dwmw@amazon.co.uk>

A previous implementation of this stuff used a 64-bit field for all of
the port information (vcpu/type/type_val) and did atomic exchanges on
them. When I implemented that in Qemu I regretted my life choices and
just kept it simple with locking instead.

So there's no need for the XenEvtchnPort to be so simplistic. We can
use a union for the pirq/virq/interdomain information, which lets us
keep a separate bit for the 'remote domain' in interdomain ports. A
single bit is enough since the only possible targets are loopback or
qemu itself.

So now we can ditch PORT_INFO_TYPEVAL_REMOTE_QEMU and the horrid
manual masking, although the in-memory representation is identical
so there's no change in the saved state ABI.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
---
hw/i386/kvm/xen_evtchn.c | 151 ++++++++++++++++++---------------------
1 file changed, 70 insertions(+), 81 deletions(-)

diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c
index b2b4be9983..02b8cbf8df 100644
--- a/hw/i386/kvm/xen_evtchn.c
+++ b/hw/i386/kvm/xen_evtchn.c
@@ -58,7 +58,15 @@ OBJECT_DECLARE_SIMPLE_TYPE(XenEvtchnState, XEN_EVTCHN)
typedef struct XenEvtchnPort {
uint32_t vcpu; /* Xen/ACPI vcpu_id */
uint16_t type; /* EVTCHNSTAT_xxxx */
- uint16_t type_val; /* pirq# / virq# / remote port according to type */
+ union {
+ uint16_t val; /* raw value for serialization etc. */
+ uint16_t pirq;
+ uint16_t virq;
+ struct {
+ uint16_t port:15;
+ uint16_t to_qemu:1; /* Only two targets; qemu or loopback */
+ } interdomain;
+ } u;
} XenEvtchnPort;

/* 32-bit compatibility definitions, also used natively in 32-bit build */
@@ -105,14 +113,6 @@ struct xenevtchn_handle {
int fd;
};

-/*
- * For unbound/interdomain ports there are only two possible remote
- * domains; self and QEMU. Use a single high bit in type_val for that,
- * and the low bits for the remote port number (or 0 for unbound).
- */
-#define PORT_INFO_TYPEVAL_REMOTE_QEMU 0x8000
-#define PORT_INFO_TYPEVAL_REMOTE_PORT_MASK 0x7FFF
-
/*
* These 'emuirq' values are used by Xen in the LM stream... and yes, I am
* insane enough to think about guest-transparent live migration from actual
@@ -210,16 +210,16 @@ static int xen_evtchn_post_load(void *opaque, int version_id)
XenEvtchnPort *p = &s->port_table[i];

if (p->type == EVTCHNSTAT_pirq) {
- assert(p->type_val);
- assert(p->type_val < s->nr_pirqs);
+ assert(p->u.pirq);
+ assert(p->u.pirq < s->nr_pirqs);

/*
* Set the gsi to IRQ_UNBOUND; it may be changed to an actual
* GSI# below, or to IRQ_MSI_EMU when the MSI table snooping
* catches up with it.
*/
- s->pirq[p->type_val].gsi = IRQ_UNBOUND;
- s->pirq[p->type_val].port = i;
+ s->pirq[p->u.pirq].gsi = IRQ_UNBOUND;
+ s->pirq[p->u.pirq].port = i;
}
}
/* Rebuild s->pirq[].gsi mapping */
@@ -243,7 +243,7 @@ static const VMStateDescription xen_evtchn_port_vmstate = {
.fields = (VMStateField[]) {
VMSTATE_UINT32(vcpu, XenEvtchnPort),
VMSTATE_UINT16(type, XenEvtchnPort),
- VMSTATE_UINT16(type_val, XenEvtchnPort),
+ VMSTATE_UINT16(u.val, XenEvtchnPort),
VMSTATE_END_OF_LIST()
}
};
@@ -605,14 +605,13 @@ static void unbind_backend_ports(XenEvtchnState *s)

for (i = 1; i < s->nr_ports; i++) {
p = &s->port_table[i];
- if (p->type == EVTCHNSTAT_interdomain &&
- (p->type_val & PORT_INFO_TYPEVAL_REMOTE_QEMU)) {
- evtchn_port_t be_port = p->type_val & PORT_INFO_TYPEVAL_REMOTE_PORT_MASK;
+ if (p->type == EVTCHNSTAT_interdomain && p->u.interdomain.to_qemu) {
+ evtchn_port_t be_port = p->u.interdomain.port;

if (s->be_handles[be_port]) {
/* This part will be overwritten on the load anyway. */
p->type = EVTCHNSTAT_unbound;
- p->type_val = PORT_INFO_TYPEVAL_REMOTE_QEMU;
+ p->u.interdomain.port = 0;

/* Leave the backend port open and unbound too. */
if (kvm_xen_has_cap(EVTCHN_SEND)) {
@@ -650,30 +649,22 @@ int xen_evtchn_status_op(struct evtchn_status *status)

switch (p->type) {
case EVTCHNSTAT_unbound:
- if (p->type_val & PORT_INFO_TYPEVAL_REMOTE_QEMU) {
- status->u.unbound.dom = DOMID_QEMU;
- } else {
- status->u.unbound.dom = xen_domid;
- }
+ status->u.unbound.dom = p->u.interdomain.to_qemu ? DOMID_QEMU
+ : xen_domid;
break;

case EVTCHNSTAT_interdomain:
- if (p->type_val & PORT_INFO_TYPEVAL_REMOTE_QEMU) {
- status->u.interdomain.dom = DOMID_QEMU;
- } else {
- status->u.interdomain.dom = xen_domid;
- }
-
- status->u.interdomain.port = p->type_val &
- PORT_INFO_TYPEVAL_REMOTE_PORT_MASK;
+ status->u.interdomain.dom = p->u.interdomain.to_qemu ? DOMID_QEMU
+ : xen_domid;
+ status->u.interdomain.port = p->u.interdomain.port;
break;

case EVTCHNSTAT_pirq:
- status->u.pirq = p->type_val;
+ status->u.pirq = p->u.pirq;
break;

case EVTCHNSTAT_virq:
- status->u.virq = p->type_val;
+ status->u.virq = p->u.virq;
break;
}

@@ -989,7 +980,7 @@ static int clear_port_pending(XenEvtchnState *s, evtchn_port_t port)
static void free_port(XenEvtchnState *s, evtchn_port_t port)
{
s->port_table[port].type = EVTCHNSTAT_closed;
- s->port_table[port].type_val = 0;
+ s->port_table[port].u.val = 0;
s->port_table[port].vcpu = 0;

if (s->nr_ports == port + 1) {
@@ -1012,7 +1003,7 @@ static int allocate_port(XenEvtchnState *s, uint32_t vcpu, uint16_t type,
if (s->port_table[p].type == EVTCHNSTAT_closed) {
s->port_table[p].vcpu = vcpu;
s->port_table[p].type = type;
- s->port_table[p].type_val = val;
+ s->port_table[p].u.val = val;

*port = p;

@@ -1053,15 +1044,15 @@ static int close_port(XenEvtchnState *s, evtchn_port_t port,
return -ENOENT;

case EVTCHNSTAT_pirq:
- s->pirq[p->type_val].port = 0;
- if (s->pirq[p->type_val].is_translated) {
+ s->pirq[p->u.pirq].port = 0;
+ if (s->pirq[p->u.pirq].is_translated) {
*flush_kvm_routes = true;
}
break;

case EVTCHNSTAT_virq:
- kvm_xen_set_vcpu_virq(virq_is_global(p->type_val) ? 0 : p->vcpu,
- p->type_val, 0);
+ kvm_xen_set_vcpu_virq(virq_is_global(p->u.virq) ? 0 : p->vcpu,
+ p->u.virq, 0);
break;

case EVTCHNSTAT_ipi:
@@ -1071,8 +1062,8 @@ static int close_port(XenEvtchnState *s, evtchn_port_t port,
break;

case EVTCHNSTAT_interdomain:
- if (p->type_val & PORT_INFO_TYPEVAL_REMOTE_QEMU) {
- uint16_t be_port = p->type_val & ~PORT_INFO_TYPEVAL_REMOTE_QEMU;
+ if (p->u.interdomain.to_qemu) {
+ uint16_t be_port = p->u.interdomain.port;
struct xenevtchn_handle *xc = s->be_handles[be_port];
if (xc) {
if (kvm_xen_has_cap(EVTCHN_SEND)) {
@@ -1082,14 +1073,15 @@ static int close_port(XenEvtchnState *s, evtchn_port_t port,
}
} else {
/* Loopback interdomain */
- XenEvtchnPort *rp = &s->port_table[p->type_val];
- if (!valid_port(p->type_val) || rp->type_val != port ||
+ XenEvtchnPort *rp = &s->port_table[p->u.interdomain.port];
+ if (!valid_port(p->u.interdomain.port) ||
+ rp->u.interdomain.port != port ||
rp->type != EVTCHNSTAT_interdomain) {
error_report("Inconsistent state for interdomain unbind");
} else {
/* Set the other end back to unbound */
rp->type = EVTCHNSTAT_unbound;
- rp->type_val = 0;
+ rp->u.interdomain.port = 0;
}
}
break;
@@ -1214,7 +1206,7 @@ int xen_evtchn_bind_vcpu_op(struct evtchn_bind_vcpu *vcpu)
if (p->type == EVTCHNSTAT_interdomain ||
p->type == EVTCHNSTAT_unbound ||
p->type == EVTCHNSTAT_pirq ||
- (p->type == EVTCHNSTAT_virq && virq_is_global(p->type_val))) {
+ (p->type == EVTCHNSTAT_virq && virq_is_global(p->u.virq))) {
/*
* unmask_port() with do_unmask==false will just raise the event
* on the new vCPU if the port was already pending.
@@ -1359,19 +1351,15 @@ int xen_evtchn_bind_ipi_op(struct evtchn_bind_ipi *ipi)
int xen_evtchn_bind_interdomain_op(struct evtchn_bind_interdomain *interdomain)
{
XenEvtchnState *s = xen_evtchn_singleton;
- uint16_t type_val;
int ret;

if (!s) {
return -ENOTSUP;
}

- if (interdomain->remote_dom == DOMID_QEMU) {
- type_val = PORT_INFO_TYPEVAL_REMOTE_QEMU;
- } else if (interdomain->remote_dom == DOMID_SELF ||
- interdomain->remote_dom == xen_domid) {
- type_val = 0;
- } else {
+ if (interdomain->remote_dom != DOMID_QEMU &&
+ interdomain->remote_dom != DOMID_SELF &&
+ interdomain->remote_dom != xen_domid) {
return -ESRCH;
}

@@ -1382,8 +1370,8 @@ int xen_evtchn_bind_interdomain_op(struct evtchn_bind_interdomain *interdomain)
qemu_mutex_lock(&s->port_lock);

/* The newly allocated port starts out as unbound */
- ret = allocate_port(s, 0, EVTCHNSTAT_unbound, type_val,
- &interdomain->local_port);
+ ret = allocate_port(s, 0, EVTCHNSTAT_unbound, 0, &interdomain->local_port);
+
if (ret) {
goto out;
}
@@ -1408,7 +1396,8 @@ int xen_evtchn_bind_interdomain_op(struct evtchn_bind_interdomain *interdomain)
assign_kernel_eventfd(lp->type, xc->guest_port, xc->fd);
}
lp->type = EVTCHNSTAT_interdomain;
- lp->type_val = PORT_INFO_TYPEVAL_REMOTE_QEMU | interdomain->remote_port;
+ lp->u.interdomain.to_qemu = 1;
+ lp->u.interdomain.port = interdomain->remote_port;
ret = 0;
} else {
/* Loopback */
@@ -1416,19 +1405,18 @@ int xen_evtchn_bind_interdomain_op(struct evtchn_bind_interdomain *interdomain)
XenEvtchnPort *lp = &s->port_table[interdomain->local_port];

/*
- * The 'remote' port for loopback must be an unbound port allocated for
- * communication with the local domain (as indicated by rp->type_val
- * being zero, not PORT_INFO_TYPEVAL_REMOTE_QEMU), and must *not* be
- * the port that was just allocated for the local end.
+ * The 'remote' port for loopback must be an unbound port allocated
+ * for communication with the local domain, and must *not* be the
+ * port that was just allocated for the local end.
*/
if (interdomain->local_port != interdomain->remote_port &&
- rp->type == EVTCHNSTAT_unbound && rp->type_val == 0) {
+ rp->type == EVTCHNSTAT_unbound && !rp->u.interdomain.to_qemu) {

rp->type = EVTCHNSTAT_interdomain;
- rp->type_val = interdomain->local_port;
+ rp->u.interdomain.port = interdomain->local_port;

lp->type = EVTCHNSTAT_interdomain;
- lp->type_val = interdomain->remote_port;
+ lp->u.interdomain.port = interdomain->remote_port;
} else {
ret = -EINVAL;
}
@@ -1447,7 +1435,6 @@ int xen_evtchn_bind_interdomain_op(struct evtchn_bind_interdomain *interdomain)
int xen_evtchn_alloc_unbound_op(struct evtchn_alloc_unbound *alloc)
{
XenEvtchnState *s = xen_evtchn_singleton;
- uint16_t type_val;
int ret;

if (!s) {
@@ -1458,18 +1445,20 @@ int xen_evtchn_alloc_unbound_op(struct evtchn_alloc_unbound *alloc)
return -ESRCH;
}

- if (alloc->remote_dom == DOMID_QEMU) {
- type_val = PORT_INFO_TYPEVAL_REMOTE_QEMU;
- } else if (alloc->remote_dom == DOMID_SELF ||
- alloc->remote_dom == xen_domid) {
- type_val = 0;
- } else {
+ if (alloc->remote_dom != DOMID_QEMU &&
+ alloc->remote_dom != DOMID_SELF &&
+ alloc->remote_dom != xen_domid) {
return -EPERM;
}

qemu_mutex_lock(&s->port_lock);

- ret = allocate_port(s, 0, EVTCHNSTAT_unbound, type_val, &alloc->port);
+ ret = allocate_port(s, 0, EVTCHNSTAT_unbound, 0, &alloc->port);
+
+ if (!ret && alloc->remote_dom == DOMID_QEMU) {
+ XenEvtchnPort *p = &s->port_table[alloc->port];
+ p->u.interdomain.to_qemu = 1;
+ }

qemu_mutex_unlock(&s->port_lock);

@@ -1496,12 +1485,12 @@ int xen_evtchn_send_op(struct evtchn_send *send)

switch (p->type) {
case EVTCHNSTAT_interdomain:
- if (p->type_val & PORT_INFO_TYPEVAL_REMOTE_QEMU) {
+ if (p->u.interdomain.to_qemu) {
/*
* This is an event from the guest to qemu itself, which is
* serving as the driver domain.
*/
- uint16_t be_port = p->type_val & ~PORT_INFO_TYPEVAL_REMOTE_QEMU;
+ uint16_t be_port = p->u.interdomain.port;
struct xenevtchn_handle *xc = s->be_handles[be_port];
if (xc) {
eventfd_write(xc->fd, 1);
@@ -1511,7 +1500,7 @@ int xen_evtchn_send_op(struct evtchn_send *send)
}
} else {
/* Loopback interdomain ports; just a complex IPI */
- set_port_pending(s, p->type_val);
+ set_port_pending(s, p->u.interdomain.port);
}
break;

@@ -1553,8 +1542,7 @@ int xen_evtchn_set_port(uint16_t port)

/* QEMU has no business sending to anything but these */
if (p->type == EVTCHNSTAT_virq ||
- (p->type == EVTCHNSTAT_interdomain &&
- (p->type_val & PORT_INFO_TYPEVAL_REMOTE_QEMU))) {
+ (p->type == EVTCHNSTAT_interdomain && p->u.interdomain.to_qemu)) {
set_port_pending(s, port);
ret = 0;
}
@@ -2064,7 +2052,7 @@ int xen_be_evtchn_bind_interdomain(struct xenevtchn_handle *xc, uint32_t domid,
switch (gp->type) {
case EVTCHNSTAT_interdomain:
/* Allow rebinding after migration, preserve port # if possible */
- be_port = gp->type_val & ~PORT_INFO_TYPEVAL_REMOTE_QEMU;
+ be_port = gp->u.interdomain.port;
assert(be_port != 0);
if (!s->be_handles[be_port]) {
s->be_handles[be_port] = xc;
@@ -2085,7 +2073,8 @@ int xen_be_evtchn_bind_interdomain(struct xenevtchn_handle *xc, uint32_t domid,
}

gp->type = EVTCHNSTAT_interdomain;
- gp->type_val = be_port | PORT_INFO_TYPEVAL_REMOTE_QEMU;
+ gp->u.interdomain.to_qemu = 1;
+ gp->u.interdomain.port = be_port;
xc->guest_port = guest_port;
if (kvm_xen_has_cap(EVTCHN_SEND)) {
assign_kernel_eventfd(gp->type, guest_port, xc->fd);
@@ -2130,7 +2119,7 @@ int xen_be_evtchn_unbind(struct xenevtchn_handle *xc, evtchn_port_t port)
/* This should never *not* be true */
if (gp->type == EVTCHNSTAT_interdomain) {
gp->type = EVTCHNSTAT_unbound;
- gp->type_val = PORT_INFO_TYPEVAL_REMOTE_QEMU;
+ gp->u.interdomain.port = 0;
}

if (kvm_xen_has_cap(EVTCHN_SEND)) {
@@ -2284,11 +2273,11 @@ EvtchnInfoList *qmp_xen_event_list(Error **errp)

info->type = p->type;
if (p->type == EVTCHNSTAT_interdomain) {
- info->remote_domain = g_strdup((p->type_val & PORT_INFO_TYPEVAL_REMOTE_QEMU) ?
+ info->remote_domain = g_strdup(p->u.interdomain.to_qemu ?
"qemu" : "loopback");
- info->target = p->type_val & PORT_INFO_TYPEVAL_REMOTE_PORT_MASK;
+ info->target = p->u.interdomain.port;
} else {
- info->target = p->type_val;
+ info->target = p->u.val; /* pirq# or virq# */
}
info->vcpu = p->vcpu;
info->pending = test_bit(i, pending);
--
2.40.1