KVM: s390: ucontrol: interface to inject faults on a vcpu page table

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@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 5ebf47d99e56378cf29c65f2e2df98093f265d4b..a67fb35993fa9eabde0d6ea061b6518d41f48c98 100644 (file)
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1539,6 +1539,22 @@ This ioctl unmaps the memory in the vcpu's address space starting at
 "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

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 5b5c28e471df31861962afe48f9a1505a7ce113c..8489edf80c89d65a8ef51309414ee5259ac704cb 100644 (file)
--- 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 *filp,
                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;
        }

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 8f888df206a28a1569934e50b64af0cc77e48672..778e748927b44866471392ab849bed5a71768f75 100644 (file)
--- 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)