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KVM: x86: Add ioctl for KVM_KVMCLOCK_CTRL

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Now that we have a flag that will tell the guest it was suspended, create an
interface for that communication using a KVM ioctl.

Signed-off-by: Eric B Munson <emunson@mgebm.net>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Eric B Munson
2012-03-10 14:37:27 -05:00
committed by Avi Kivity
parent 3b5d56b931
commit 1c0b28c2a4
4 changed files with 49 additions and 0 deletions
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20
Documentation/virtual/kvm/api.txt
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@@ -1669,6 +1669,26 @@ at the memory location pointed to by "addr".
The list of registers accessible using this interface is identical to the
list in 4.64.
4.70 KVM_KVMCLOCK_CTRL
Capability: KVM_CAP_KVMCLOCK_CTRL
Architectures: Any that implement pvclocks (currently x86 only)
Type: vcpu ioctl
Parameters: None
Returns: 0 on success, -1 on error
This signals to the host kernel that the specified guest is being paused by
userspace. The host will set a flag in the pvclock structure that is checked
from the soft lockup watchdog. The flag is part of the pvclock structure that
is shared between guest and host, specifically the second bit of the flags
field of the pvclock_vcpu_time_info structure. It will be set exclusively by
the host and read/cleared exclusively by the guest. The guest operation of
checking and clearing the flag must an atomic operation so
load-link/store-conditional, or equivalent must be used. There are two cases
where the guest will clear the flag: when the soft lockup watchdog timer resets
itself or when a soft lockup is detected. This ioctl can be called any time
after pausing the vcpu, but before it is resumed.
5. The kvm_run structure
Application code obtains a pointer to the kvm_run structure by