diff options
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/kvm/api.txt | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt index 4833904d32a5..7403f15657c2 100644 --- a/Documentation/virt/kvm/api.txt +++ b/Documentation/virt/kvm/api.txt @@ -4468,6 +4468,39 @@ Hyper-V SynIC state change. Notification is used to remap SynIC event/message pages and to enable/disable SynIC messages/events processing in userspace. + /* KVM_EXIT_ARM_NISV */ + struct { + __u64 esr_iss; + __u64 fault_ipa; + } arm_nisv; + +Used on arm and arm64 systems. If a guest accesses memory not in a memslot, +KVM will typically return to userspace and ask it to do MMIO emulation on its +behalf. However, for certain classes of instructions, no instruction decode +(direction, length of memory access) is provided, and fetching and decoding +the instruction from the VM is overly complicated to live in the kernel. + +Historically, when this situation occurred, KVM would print a warning and kill +the VM. KVM assumed that if the guest accessed non-memslot memory, it was +trying to do I/O, which just couldn't be emulated, and the warning message was +phrased accordingly. However, what happened more often was that a guest bug +caused access outside the guest memory areas which should lead to a more +meaningful warning message and an external abort in the guest, if the access +did not fall within an I/O window. + +Userspace implementations can query for KVM_CAP_ARM_NISV_TO_USER, and enable +this capability at VM creation. Once this is done, these types of errors will +instead return to userspace with KVM_EXIT_ARM_NISV, with the valid bits from +the HSR (arm) and ESR_EL2 (arm64) in the esr_iss field, and the faulting IPA +in the fault_ipa field. Userspace can either fix up the access if it's +actually an I/O access by decoding the instruction from guest memory (if it's +very brave) and continue executing the guest, or it can decide to suspend, +dump, or restart the guest. + +Note that KVM does not skip the faulting instruction as it does for +KVM_EXIT_MMIO, but userspace has to emulate any change to the processing state +if it decides to decode and emulate the instruction. + /* Fix the size of the union. */ char padding[256]; }; |