[PATCH v7 0/3] KVM: s390: Introducing kvm_arch_set_irq_inatomic Fast Inject

[Douglas Freimuth <freimuth@linux.ibm.com>]

s390 needs this series of three patches in order to enable a non-blocking
path for irqfd injection on s390 via kvm_arch_set_irq_inatomic(). Before
these changes, kvm_arch_set_irq_inatomic() would just return -EWOULDBLOCK
and place all interrupts on the global work queue, which must subsequently
be processed by a different thread. This series of patches implements an
s390 version of inatomic and is relevant to virtio-blk and virtio-net and
was tested against virtio-pci and virtio-ccw.

The inatomic fast path cannot lose control since it is running with
interrupts disabled. This meant making the following changes that exist on
the slow path today. First, the adapter_indicators page needs to be mapped
since it is accessed with interrupts disabled, so we added map/unmap
functions. Second, access to shared resources between the fast and slow
paths needed to be changed from mutex and semaphores to spin_lock's.
Finally, the memory allocation on the slow path utilizes GFP_KERNEL_ACCOUNT
but we had to implement the fast path with GFP_ATOMIC allocation. Each of
these enhancements were required to prevent blocking on the fast inject
path.

s390 doesn't support a PREEMPT_RT kernel and this patch doesn't either.
Given this fact, we are not using raw_spin_lock instead we are using
regular spin_lock.

Statistical counters have been added to enable analysis of irq injection on
the fast path and slow path including io_390_inatomic, io_flic_inject_airq,
io_set_adapter_int and io_390_inatomic_adapter_masked. And counters have
been added to analyze map/unmap of the adapter_indicator
pages in non-Secure Execution environments and to track fencing of Fast
Inject in Secure Execution environments. In order to take advantage of this
kernel series with virtio-pci, a QEMU that includes the
's390x/pci: set kvm_msi_via_irqfd_allowed' fix is needed.  Additionally,
the guest xml needs a thread pool and threads explicitly assigned per disk
device using the common way of defining threads for disks.

Patch 1 enables map/unmap of adapter indicator pages but for Secure
Execution environments it avoids the long term mapping.

v6->v7: Drop all raw_spin_lock in previous patch and make them spin_locks.
v6->v7: Hold the kvm->lock in register_io_adapter.
v6->v7: Call kvm_s390_unmap_all_adapters() directly in kvm_s390_handle_pv.
v6->v7: Simplify unpin logic in adapter_indicators_set.
v6->v7: Make the caller of kvm_s390_inject_vm() kfree(inti)

Douglas Freimuth (3):
  KVM: s390: Add map/unmap ioctl and clean mappings post-guest
  KVM: s390: Enable adapter_indicators_set to use mapped pages
  KVM: s390: Introducing kvm_arch_set_irq_inatomic fast inject

 arch/s390/include/asm/kvm_host.h |  11 +-
 arch/s390/kvm/interrupt.c        | 444 ++++++++++++++++++++++++++-----
 arch/s390/kvm/kvm-s390.c         |  30 ++-
 arch/s390/kvm/kvm-s390.h         |   5 +-
 4 files changed, 418 insertions(+), 72 deletions(-)

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2.54.0