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    KVM: PPC: Book3S HV: Handle passthrough interrupts in guest · e3c13e56
    Suresh Warrier 提交于
    Currently, KVM switches back to the host to handle any external
    interrupt (when the interrupt is received while running in the
    guest). This patch updates real-mode KVM to check if an interrupt
    is generated by a passthrough adapter that is owned by this guest.
    If so, the real mode KVM will directly inject the corresponding
    virtual interrupt to the guest VCPU's ICS and also EOI the interrupt
    in hardware. In short, the interrupt is handled entirely in real
    mode in the guest context without switching back to the host.
    
    In some rare cases, the interrupt cannot be completely handled in
    real mode, for instance, a VCPU that is sleeping needs to be woken
    up. In this case, KVM simply switches back to the host with trap
    reason set to 0x500. This works, but it is clearly not very efficient.
    A following patch will distinguish this case and handle it
    correctly in the host. Note that we can use the existing
    check_too_hard() routine even though we are not in a hypercall to
    determine if there is unfinished business that needs to be
    completed in host virtual mode.
    
    The patch assumes that the mapping between hardware interrupt IRQ
    and virtual IRQ to be injected to the guest already exists for the
    PCI passthrough interrupts that need to be handled in real mode.
    If the mapping does not exist, KVM falls back to the default
    existing behavior.
    
    The KVM real mode code reads mappings from the mapped array in the
    passthrough IRQ map without taking any lock.  We carefully order the
    loads and stores of the fields in the kvmppc_irq_map data structure
    using memory barriers to avoid an inconsistent mapping being seen by
    the reader. Thus, although it is possible to miss a map entry, it is
    not possible to read a stale value.
    
    [paulus@ozlabs.org - get irq_chip from irq_map rather than pimap,
     pulled out powernv eoi change into a separate patch, made
     kvmppc_read_intr get the vcpu from the paca rather than being
     passed in, rewrote the logic at the end of kvmppc_read_intr to
     avoid deep indentation, simplified logic in book3s_hv_rmhandlers.S
     since we were always restoring SRR0/1 anyway, get rid of the cached
     array (just use the mapped array), removed the kick_all_cpus_sync()
     call, clear saved_xirr PACA field when we handle the interrupt in
     real mode, fix compilation with CONFIG_KVM_XICS=n.]
    Signed-off-by: NSuresh Warrier <warrier@linux.vnet.ibm.com>
    Signed-off-by: NPaul Mackerras <paulus@ozlabs.org>
    e3c13e56
book3s_hv.c 95.1 KB