linux-toradex.git/include/linux/kvm.h, branch tegra-10.7.1

KVM: allow userspace to adjust kvmclock offset

2010-02-09T12:50:56+00:00

(cherry picked from afbcf7ab8d1bc8c2d04792f6d9e786e0adeb328d)

When we migrate a kvm guest that uses pvclock between two hosts, we may
suffer a large skew. This is because there can be significant differences
between the monotonic clock of the hosts involved. When a new host with
a much larger monotonic time starts running the guest, the view of time
will be significantly impacted.

Situation is much worse when we do the opposite, and migrate to a host with
a smaller monotonic clock.

This proposed ioctl will allow userspace to inform us what is the monotonic
clock value in the source host, so we can keep the time skew short, and
more importantly, never goes backwards. Userspace may also need to trigger
the current data, since from the first migration onwards, it won't be
reflected by a simple call to clock_gettime() anymore.

[marcelo: future-proof abi with a flags field]
[jan: fix KVM_GET_CLOCK by clearing flags field instead of checking it]

Signed-off-by: Glauber Costa 
Signed-off-by: Marcelo Tosatti 
Signed-off-by: Avi Kivity 
Signed-off-by: Greg Kroah-Hartman

KVM: s390: Make psw available on all exits, not just a subset

2009-12-18T22:03:35+00:00

commit d7b0b5eb3000c6fb902f08c619fcd673a23d8fab upstream.

This patch moves s390 processor status word into the base kvm_run
struct and keeps it up-to date on all userspace exits.

The userspace ABI is broken by this, however there are no applications
in the wild using this.  A capability check is provided so users can
verify the updated API exists.

Signed-off-by: Carsten Otte 
Signed-off-by: Avi Kivity 
Signed-off-by: Greg Kroah-Hartman

KVM: VMX: Introduce KVM_SET_IDENTITY_MAP_ADDR ioctl

2009-09-10T05:33:16+00:00

Now KVM allow guest to modify guest's physical address of EPT's identity mapping page.

(change from v1, discard unnecessary check, change ioctl to accept parameter
address rather than value)

Signed-off-by: Sheng Yang 
Signed-off-by: Marcelo Tosatti

KVM: add ioeventfd support

2009-09-10T05:33:12+00:00

ioeventfd is a mechanism to register PIO/MMIO regions to trigger an eventfd
signal when written to by a guest.  Host userspace can register any
arbitrary IO address with a corresponding eventfd and then pass the eventfd
to a specific end-point of interest for handling.

Normal IO requires a blocking round-trip since the operation may cause
side-effects in the emulated model or may return data to the caller.
Therefore, an IO in KVM traps from the guest to the host, causes a VMX/SVM
"heavy-weight" exit back to userspace, and is ultimately serviced by qemu's
device model synchronously before returning control back to the vcpu.

However, there is a subclass of IO which acts purely as a trigger for
other IO (such as to kick off an out-of-band DMA request, etc).  For these
patterns, the synchronous call is particularly expensive since we really
only want to simply get our notification transmitted asychronously and
return as quickly as possible.  All the sychronous infrastructure to ensure
proper data-dependencies are met in the normal IO case are just unecessary
overhead for signalling.  This adds additional computational load on the
system, as well as latency to the signalling path.

Therefore, we provide a mechanism for registration of an in-kernel trigger
point that allows the VCPU to only require a very brief, lightweight
exit just long enough to signal an eventfd.  This also means that any
clients compatible with the eventfd interface (which includes userspace
and kernelspace equally well) can now register to be notified. The end
result should be a more flexible and higher performance notification API
for the backend KVM hypervisor and perhipheral components.

To test this theory, we built a test-harness called "doorbell".  This
module has a function called "doorbell_ring()" which simply increments a
counter for each time the doorbell is signaled.  It supports signalling
from either an eventfd, or an ioctl().

We then wired up two paths to the doorbell: One via QEMU via a registered
io region and through the doorbell ioctl().  The other is direct via
ioeventfd.

You can download this test harness here:

ftp://ftp.novell.com/dev/ghaskins/doorbell.tar.bz2

The measured results are as follows:

qemu-mmio:       110000 iops, 9.09us rtt
ioeventfd-mmio: 200100 iops, 5.00us rtt
ioeventfd-pio:  367300 iops, 2.72us rtt

I didn't measure qemu-pio, because I have to figure out how to register a
PIO region with qemu's device model, and I got lazy.  However, for now we
can extrapolate based on the data from the NULLIO runs of +2.56us for MMIO,
and -350ns for HC, we get:

qemu-pio:      153139 iops, 6.53us rtt
ioeventfd-hc: 412585 iops, 2.37us rtt

these are just for fun, for now, until I can gather more data.

Here is a graph for your convenience:

http://developer.novell.com/wiki/images/7/76/Iofd-chart.png

The conclusion to draw is that we save about 4us by skipping the userspace
hop.

--------------------

Signed-off-by: Gregory Haskins 
Acked-by: Michael S. Tsirkin 
Signed-off-by: Avi Kivity

KVM: PIT support for HPET legacy mode

2009-09-10T05:33:12+00:00

When kvm is in hpet_legacy_mode, the hpet is providing the timer
interrupt and the pit should not be. So in legacy mode, the pit timer
is destroyed, but the *state* of the pit is maintained. So if kvm or
the guest tries to modify the state of the pit, this modification is
accepted, *except* that the timer isn't actually started. When we exit
hpet_legacy_mode, the current state of the pit (which is up to date
since we've been accepting modifications) is used to restart the pit
timer.

The saved_mode code in kvm_pit_load_count temporarily changes mode to
0xff in order to destroy the timer, but then restores the actual
value, again maintaining "current" state of the pit for possible later
reenablement.

[avi: add some reserved storage in the ioctl; make SET_PIT2 IOW]
[marcelo: fix memory corruption due to reserved storage]

Signed-off-by: Beth Kon 
Signed-off-by: Marcelo Tosatti 
Signed-off-by: Avi Kivity

KVM: remove old KVMTRACE support code

2009-09-10T05:33:03+00:00

Return EOPNOTSUPP for KVM_TRACE_ENABLE/PAUSE/DISABLE ioctls.

Signed-off-by: Marcelo Tosatti 
Signed-off-by: Avi Kivity

KVM: Return to userspace on emulation failure

2009-09-10T05:32:52+00:00

Instead of mindlessly retrying to execute the instruction, report the
failure to userspace.

Signed-off-by: Avi Kivity

KVM: Break dependency between vcpu index in vcpus array and vcpu_id.

2009-09-10T05:32:52+00:00

Archs are free to use vcpu_id as they see fit. For x86 it is used as
vcpu's apic id. New ioctl is added to configure boot vcpu id that was
assumed to be 0 till now.

Signed-off-by: Gleb Natapov 
Signed-off-by: Avi Kivity

KVM: Reorder ioctls in kvm.h

2009-09-10T05:32:50+00:00

Somehow the VM ioctls got unsorted; resort.

Signed-off-by: Avi Kivity

KVM: Downsize max support MSI-X entry to 256

2009-09-10T05:32:43+00:00

We only trap one page for MSI-X entry now, so it's 4k/(128/8) = 256 entries at
most.

Signed-off-by: Sheng Yang 
Signed-off-by: Avi Kivity