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Commit ccc7910f authored by Carsten Otte's avatar Carsten Otte Committed by Avi Kivity
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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: default avatarCarsten Otte <cotte@de.ibm.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent d6b6d166

Documentation/virtual/kvm/api.txt

+16 −0
Original line number Diff line number Diff line
@@ -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

arch/s390/kvm/kvm-s390.c

+6 −0
Original line number Diff line number Diff line
@@ -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;

	}

include/linux/kvm.h

+1 −0
Original line number Diff line number Diff line
@@ -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)