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

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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>
This commit is contained in:
Carsten Otte 2012-01-04 10:25:26 +01:00 committed by Avi Kivity
parent d6b6d16686
commit ccc7910fe5
3 changed files with 23 additions and 0 deletions
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16
Documentation/virtual/kvm/api.txt
View file

@ -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

6
arch/s390/kvm/kvm-s390.c
View file

@ -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;
}

1
include/linux/kvm.h
View file

@ -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)