[PATCH v3 4/5] KVM: add KVM_USER_EXIT vcpu ioctl for userspace exit

Radim Krčmář
2015-08-14T10:11:51Z

The guest can use KVM_USER_EXIT instead of a signal-based exiting to
userspace. Availability depends on KVM_CAP_USER_EXIT.
Only x86 is implemented so far.

Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---
v3:
* use ioctl argument directly (unsigned long as flags) [Paolo]
v2:
* use vcpu ioctl instead of vm one [Paolo]
* shrink kvm_user_exit from 64 to 32 bytes

Documentation/virtual/kvm/api.txt | 25 +++++++++++++++++++++++++
arch/x86/kvm/x86.c | 15 +++++++++++++++
include/uapi/linux/kvm.h | 3 +++
virt/kvm/kvm_main.c | 5 +++--
4 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 3c714d43a717..df087ff3c5b6 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3020,6 +3020,31 @@ Returns: 0 on success, -1 on error

Queues an SMI on the thread's vcpu.

+
+4.97 KVM_USER_EXIT
+
+Capability: KVM_CAP_USER_EXIT
+Architectures: x86
+Type: vcpu ioctl
+Parameters: unsigned long flags (in)
+Returns: 0 on success,
+ -EINVAL if flags is not 0
+
+The ioctl is asynchronous to VCPU execution and can be issued from all threads.
+
+Make vcpu_id exit to userspace as soon as possible. If the VCPU is not running
+in kernel at the time, it will exit early on the next call to KVM_RUN.
+If the VCPU was going to exit because of other reasons when KVM_USER_EXIT was
+issued, it will keep the original exit reason without exiting early on next
+KVM_RUN.
+If VCPU exited because of KVM_USER_EXIT, the exit reason is KVM_EXIT_REQUEST.
+
+This ioctl has very similar effect (same sans some races on userspace exit) as
+sending a signal (that is blocked in userspace and set in KVM_SET_SIGNAL_MASK)
+to the VCPU thread.
+
+
+
5. The kvm_run structure
------------------------

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 37db1b32684a..d985806b17b1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2467,6 +2467,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
case KVM_CAP_ASSIGN_DEV_IRQ:
case KVM_CAP_PCI_2_3:
#endif
+ case KVM_CAP_USER_EXIT:
r = 1;
break;
case KVM_CAP_X86_SMM:
@@ -3078,6 +3079,17 @@ static int kvm_set_guest_paused(struct kvm_vcpu *vcpu)
return 0;
}

+static int kvm_vcpu_ioctl_user_exit(struct kvm_vcpu *vcpu, unsigned long flags)
+{
+ if (flags != 0)
+ return -EINVAL;
+
+ kvm_make_request(KVM_REQ_EXIT, vcpu);
+ kvm_vcpu_kick(vcpu);
+
+ return 0;
+}
+
long kvm_arch_vcpu_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg)
{
@@ -3342,6 +3354,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
r = kvm_set_guest_paused(vcpu);
goto out;
}
+ case KVM_USER_EXIT:
+ r = kvm_vcpu_ioctl_user_exit(vcpu, arg);
+ break;
default:
r = -EINVAL;
}
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d996a7cdb4d2..58b3a07adc81 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -826,6 +826,7 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_X86_SMM 117
#define KVM_CAP_MULTI_ADDRESS_SPACE 118
#define KVM_CAP_SPLIT_IRQCHIP 119
+#define KVM_CAP_USER_EXIT 120

#ifdef KVM_CAP_IRQ_ROUTING

@@ -1213,6 +1214,8 @@ struct kvm_s390_ucas_mapping {
#define KVM_S390_GET_IRQ_STATE _IOW(KVMIO, 0xb6, struct kvm_s390_irq_state)
/* Available with KVM_CAP_X86_SMM */
#define KVM_SMI _IO(KVMIO, 0xb7)
+/* Available with KVM_CAP_USER_EXIT */
+#define KVM_USER_EXIT _IO(KVMIO, 0xb8)

#define KVM_DEV_ASSIGN_ENABLE_IOMMU (1 << 0)
#define KVM_DEV_ASSIGN_PCI_2_3 (1 << 1)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 347899966178..dfa2d5f27713 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2251,15 +2251,16 @@ static long kvm_vcpu_ioctl(struct file *filp,
if (unlikely(_IOC_TYPE(ioctl) != KVMIO))
return -EINVAL;

-#if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
/*
* Special cases: vcpu ioctls that are asynchronous to vcpu execution,
* so vcpu_load() would break it.
*/
+#if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
if (ioctl == KVM_S390_INTERRUPT || ioctl == KVM_S390_IRQ || ioctl == KVM_INTERRUPT)
return kvm_arch_vcpu_ioctl(filp, ioctl, arg);
#endif
-
+ if (ioctl == KVM_USER_EXIT)
+ return kvm_arch_vcpu_ioctl(filp, ioctl, arg);

r = vcpu_load(vcpu);
if (r)
--
2.5.0