Commit 40da8ccd authored by David Woodhouse's avatar David Woodhouse
Browse files

KVM: x86/xen: Add event channel interrupt vector upcall



It turns out that we can't handle event channels *entirely* in userspace
by delivering them as ExtINT, because KVM is a bit picky about when it
accepts ExtINT interrupts from a legacy PIC. The in-kernel local APIC
has to have LVT0 configured in APIC_MODE_EXTINT and unmasked, which
isn't necessarily the case for Xen guests especially on secondary CPUs.

To cope with this, add kvm_xen_get_interrupt() which checks the
evtchn_pending_upcall field in the Xen vcpu_info, and delivers the Xen
upcall vector (configured by KVM_XEN_ATTR_TYPE_UPCALL_VECTOR) if it's
set regardless of LAPIC LVT0 configuration. This gives us the minimum
support we need for completely userspace-based implementation of event
channels.

This does mean that vcpu_enter_guest() needs to check for the
evtchn_pending_upcall flag being set, because it can't rely on someone
having set KVM_REQ_EVENT unless we were to add some way for userspace to
do so manually.

Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
parent f2340cd9
......@@ -913,6 +913,7 @@ struct msr_bitmap_range {
struct kvm_xen {
bool long_mode;
bool shinfo_set;
u8 upcall_vector;
struct gfn_to_hva_cache shinfo_cache;
};
......
......@@ -14,6 +14,7 @@
#include "irq.h"
#include "i8254.h"
#include "x86.h"
#include "xen.h"
/*
* check if there are pending timer events
......@@ -56,6 +57,9 @@ int kvm_cpu_has_extint(struct kvm_vcpu *v)
if (!lapic_in_kernel(v))
return v->arch.interrupt.injected;
if (kvm_xen_has_interrupt(v))
return 1;
if (!kvm_apic_accept_pic_intr(v))
return 0;
......@@ -110,6 +114,9 @@ static int kvm_cpu_get_extint(struct kvm_vcpu *v)
if (!lapic_in_kernel(v))
return v->arch.interrupt.nr;
if (kvm_xen_has_interrupt(v))
return v->kvm->arch.xen.upcall_vector;
if (irqchip_split(v->kvm)) {
int vector = v->arch.pending_external_vector;
......
......@@ -8987,7 +8987,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
static_call(kvm_x86_msr_filter_changed)(vcpu);
}
if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
kvm_xen_has_interrupt(vcpu)) {
++vcpu->stat.req_event;
kvm_apic_accept_events(vcpu);
if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
......
......@@ -61,6 +61,44 @@ static int kvm_xen_shared_info_init(struct kvm *kvm, gfn_t gfn)
return ret;
}
int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
{
u8 rc = 0;
/*
* If the global upcall vector (HVMIRQ_callback_vector) is set and
* the vCPU's evtchn_upcall_pending flag is set, the IRQ is pending.
*/
struct gfn_to_hva_cache *ghc = &v->arch.xen.vcpu_info_cache;
struct kvm_memslots *slots = kvm_memslots(v->kvm);
unsigned int offset = offsetof(struct vcpu_info, evtchn_upcall_pending);
/* No need for compat handling here */
BUILD_BUG_ON(offsetof(struct vcpu_info, evtchn_upcall_pending) !=
offsetof(struct compat_vcpu_info, evtchn_upcall_pending));
BUILD_BUG_ON(sizeof(rc) !=
sizeof(((struct vcpu_info *)0)->evtchn_upcall_pending));
BUILD_BUG_ON(sizeof(rc) !=
sizeof(((struct compat_vcpu_info *)0)->evtchn_upcall_pending));
/*
* For efficiency, this mirrors the checks for using the valid
* cache in kvm_read_guest_offset_cached(), but just uses
* __get_user() instead. And falls back to the slow path.
*/
if (likely(slots->generation == ghc->generation &&
!kvm_is_error_hva(ghc->hva) && ghc->memslot)) {
/* Fast path */
__get_user(rc, (u8 __user *)ghc->hva + offset);
} else {
/* Slow path */
kvm_read_guest_offset_cached(v->kvm, ghc, &rc, offset,
sizeof(rc));
}
return rc;
}
int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
{
int r = -ENOENT;
......@@ -83,6 +121,16 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
r = kvm_xen_shared_info_init(kvm, data->u.shared_info.gfn);
break;
case KVM_XEN_ATTR_TYPE_UPCALL_VECTOR:
if (data->u.vector < 0x10)
r = -EINVAL;
else {
kvm->arch.xen.upcall_vector = data->u.vector;
r = 0;
}
break;
default:
break;
}
......@@ -110,6 +158,11 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
}
break;
case KVM_XEN_ATTR_TYPE_UPCALL_VECTOR:
data->u.vector = kvm->arch.xen.upcall_vector;
r = 0;
break;
default:
break;
}
......
......@@ -13,6 +13,7 @@
extern struct static_key_false_deferred kvm_xen_enabled;
int __kvm_xen_has_interrupt(struct kvm_vcpu *vcpu);
int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
......@@ -29,6 +30,14 @@ static inline bool kvm_xen_hypercall_enabled(struct kvm *kvm)
KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL);
}
static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
{
if (static_branch_unlikely(&kvm_xen_enabled.key) &&
vcpu->arch.xen.vcpu_info_set && vcpu->kvm->arch.xen.upcall_vector)
return __kvm_xen_has_interrupt(vcpu);
return 0;
}
/* 32-bit compatibility definitions, also used natively in 32-bit build */
#include <asm/pvclock-abi.h>
......
......@@ -1596,6 +1596,7 @@ struct kvm_xen_hvm_attr {
__u16 pad[3];
union {
__u8 long_mode;
__u8 vector;
struct {
__u64 gfn;
} shared_info;
......@@ -1605,6 +1606,7 @@ struct kvm_xen_hvm_attr {
#define KVM_XEN_ATTR_TYPE_LONG_MODE 0x0
#define KVM_XEN_ATTR_TYPE_SHARED_INFO 0x1
#define KVM_XEN_ATTR_TYPE_UPCALL_VECTOR 0x2
/* Per-vCPU Xen attributes */
#define KVM_XEN_VCPU_GET_ATTR _IOWR(KVMIO, 0xca, struct kvm_xen_vcpu_attr)
......
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