This patch allows the user to fault in pages on a virtual cpus
address space for user controlled virtual machines. Typically this
is superfluous because userspace can just create a mapping and
let the kernel's page fault logic take are of it. There is one
exception: SIE won't start if the lowcore is not present. Normally
the kernel takes care of this [handle_validity() in
arch/s390/kvm/intercept.c] but since the kernel does not handle
intercepts for user controlled virtual machines, userspace needs to
be able to handle this condition.
Signed-off-by: Carsten Otte <cotte@xxxxxxxxxx>
---
---
Documentation/virtual/kvm/api.txt | 16 ++++++++++++++++
arch/s390/kvm/kvm-s390.c | 6 ++++++
include/linux/kvm.h | 1 +
3 files changed, 23 insertions(+)
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1539,6 +1539,22 @@ This ioctl unmaps the memory in the vcpu
"vcpu_addr" with the length "length". The field "user_addr" is ignored.
All parameters need to be alligned by 1 megabyte.
+4.66 KVM_S390_VCPU_FAULT
+
+Capability: KVM_CAP_S390_UCONTROL
+Architectures: s390
+Type: vcpu ioctl
+Parameters: vcpu absolute address (in)
+Returns: 0 in case of success
+
+This call creates a page table entry on the virtual cpu's address space
+(for user controlled virtual machines) or the virtual machine's address
+space (for regular virtual machines). This only works for minor faults,
+thus it's recommended to access subject memory page via the user page
+table upfront. This is useful to handle validity intercepts for user
+controlled virtual machines to fault in the virtual cpu's lowcore pages
+prior to calling the KVM_RUN ioctl.
+
5. The kvm_run structure
Application code obtains a pointer to the kvm_run structure by
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -761,6 +761,12 @@ long kvm_arch_vcpu_ioctl(struct file *fi
break;
}
#endif
+ case KVM_S390_VCPU_FAULT: {
+ r = gmap_fault(arg, vcpu->arch.gmap);
+ if (!IS_ERR_VALUE(r))
+ r = 0;
+ break;
+ }
default:
r = -EINVAL;
}
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -675,6 +675,7 @@ struct kvm_s390_ucas_mapping {
};
#define KVM_S390_UCAS_MAP _IOW(KVMIO, 0x50, struct kvm_s390_ucas_mapping)
#define KVM_S390_UCAS_UNMAP _IOW(KVMIO, 0x51, struct kvm_s390_ucas_mapping)
+#define KVM_S390_VCPU_FAULT _IOW(KVMIO, 0x52, unsigned long)
/* Device model IOC */
#define KVM_CREATE_IRQCHIP _IO(KVMIO, 0x60)
--
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