From: David Woodhouse <dwmw@xxxxxxxxxxxx>
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: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/irq.c | 7 +++++
arch/x86/kvm/x86.c | 3 +-
arch/x86/kvm/xen.c | 53 +++++++++++++++++++++++++++++++++
arch/x86/kvm/xen.h | 9 ++++++
include/uapi/linux/kvm.h | 2 ++
6 files changed, 74 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cd65bd43fc5f..9693ec3c2042 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -902,6 +902,7 @@ struct msr_bitmap_range {
struct kvm_xen {
bool long_mode;
bool shinfo_set;
+ u8 upcall_vector;
struct gfn_to_hva_cache shinfo_cache;
};
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index 814698e5b152..24668b51b5c8 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -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;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8d849e8e9953..cdcc8abf2216 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8950,7 +8950,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
kvm_x86_ops.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) {
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index bd343222e740..39a7ffcdcf22 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -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;
}
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index fb85377fdbdc..4b32489c0cec 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -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>
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index e00b15ba7b7e..c828c94dbe8b 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1594,6 +1594,7 @@ struct kvm_xen_hvm_attr {
__u16 pad[3];
union {
__u8 long_mode;
+ __u8 vector;
struct {
__u64 gfn;
} shared_info;
@@ -1603,6 +1604,7 @@ 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)
--
2.29.2
