• Paul Mackerras's avatar
    KVM: PPC: Book3S HV: Set server for passed-through interrupts · 5d375199
    Paul Mackerras authored
    When a guest has a PCI pass-through device with an interrupt, it
    will direct the interrupt to a particular guest VCPU.  In fact the
    physical interrupt might arrive on any CPU, and then get
    delivered to the target VCPU in the emulated XICS (guest interrupt
    controller), and eventually delivered to the target VCPU.
    
    Now that we have code to handle device interrupts in real mode
    without exiting to the host kernel, there is an advantage to having
    the device interrupt arrive on the same sub(core) as the target
    VCPU is running on.  In this situation, the interrupt can be
    delivered to the target VCPU without any exit to the host kernel
    (using a hypervisor doorbell interrupt between threads if
    necessary).
    
    This patch aims to get passed-through device interrupts arriving
    on the correct core by setting the interrupt server in the real
    hardware XICS for the interrupt to the first thread in the (sub)core
    where its target VCPU is running.  We do this in the real-mode H_EOI
    code because the H_EOI handler already needs to look at the
    emulated ICS state for the interrupt (whereas the H_XIRR handler
    doesn't), and we know we are running in the target VCPU context
    at that point.
    
    We set the server CPU in hardware using an OPAL call, regardless of
    what the IRQ affinity mask for the interrupt says, and without
    updating the affinity mask.  This amounts to saying that when an
    interrupt is passed through to a guest, as a matter of policy we
    allow the guest's affinity for the interrupt to override the host's.
    
    This is inspired by an earlier patch from Suresh Warrier, although
    none of this code came from that earlier patch.
    Signed-off-by: default avatarPaul Mackerras <paulus@ozlabs.org>
    5d375199
book3s_xics.c 36 KB