The GSI callback (and later PCI_INTX) is a level triggered interrupt. It
is asserted when an event channel is delivered to vCPU0, and is supposed
to be cleared when the vcpu_info->evtchn_upcall_pending field for vCPU0
is cleared again.
Thankfully, Xen does *not* assert the GSI if the guest sets its own
evtchn_upcall_pending field; we only need to assert the GSI when we
have delivered an event for ourselves. So that's the easy part, kind of.
There's a slight complexity in that we need to hold the BQL before we
can call qemu_set_irq(), and we definitely can't do that while holding
our own port_lock (because we'll need to take that from the qemu-side
functions that the PV backend drivers will call). So if we end up
wanting to set the IRQ in a context where we *don't* already hold the
BQL, defer to a BH.
However, we *do* need to poll for the evtchn_upcall_pending flag being
cleared. In an ideal world we would poll that when the EOI happens on
the PIC/IOAPIC. That's how it works in the kernel with the VFIO eventfd
pairs — one is used to trigger the interrupt, and the other works in the
other direction to 'resample' on EOI, and trigger the first eventfd
again if the line is still active.
However, QEMU doesn't seem to do that. Even VFIO level interrupts seem
to be supported by temporarily unmapping the device's BARs from the
guest when an interrupt happens, then trapping *all* MMIO to the device
and sending the 'resample' event on *every* MMIO access until the IRQ
is cleared! Maybe in future we'll plumb the 'resample' concept through
QEMU's irq framework but for now we'll do what Xen itself does: just
check the flag on every vmexit if the upcall GSI is known to be
asserted.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Handle the hypercall to set a per vcpu info, and also wire up the default
vcpu_info in the shared_info page for the first 32 vCPUs.
To avoid deadlock within KVM a vCPU thread must set its *own* vcpu_info
rather than it being set from the context in which the hypercall is
invoked.
Add the vcpu_info (and default) GPA to the vmstate_x86_cpu for migration,
and restore it in kvm_arch_put_registers() appropriately.
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
This means handling the new exit reason for Xen but still
crashing on purpose. As we implement each of the hypercalls
we will then return the right return code.
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
[dwmw2: Add CPL to hypercall tracing, disallow hypercalls from CPL > 0]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
There are (at least) three different vCPU ID number spaces. One is the
internal KVM vCPU index, based purely on which vCPU was chronologically
created in the kernel first. If userspace threads are all spawned and
create their KVM vCPUs in essentially random order, then the KVM indices
are basically random too.
The second number space is the APIC ID space, which is consistent and
useful for referencing vCPUs. MSIs will specify the target vCPU using
the APIC ID, for example, and the KVM Xen APIs also take an APIC ID
from userspace whenever a vCPU needs to be specified (as opposed to
just using the appropriate vCPU fd).
The third number space is not normally relevant to the kernel, and is
the ACPI/MADT/Xen CPU number which corresponds to cs->cpu_index. But
Xen timer hypercalls use it, and Xen timer hypercalls *really* want
to be accelerated in the kernel rather than handled in userspace, so
the kernel needs to be told.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Introduce support for emulating CPUID for Xen HVM guests. It doesn't make
sense to advertise the KVM leaves to a Xen guest, so do Xen unconditionally
when the xen-version machine property is set.
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
[dwmw2: Obtain xen_version from KVM property, make it automatic]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
This just initializes the basic Xen support in KVM for now. Only permitted
on TYPE_PC_MACHINE because that's where the sysbus devices for Xen heap
overlay, event channel, grant tables and other stuff will exist. There's
no point having the basic hypercall support if nothing else works.
Provide sysemu/kvm_xen.h and a kvm_xen_get_caps() which will be used
later by support devices.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
