[PATCH 0/2] genirq and Hyper-V: Clean up handling of add_interrupt_randomness()

[Michael Kelley]

From: Michael Kelley <mhklinux@xxxxxxxxxxx>

The Hyper-V ISRs are calling add_interrupt_randomness() as a
primary source of entropy in VMs, since the VMs don't have another
good source. The call is currently in the ISRs as a common place to
handle both x86/x64 and arm64. On x86/x64, hypervisor interrupts come
through a custom sysvec entry, and on arm64 they come through an
emulated GICv3. GICv3 uses the generic handler handle_percpu_devid_irq(),
which does not do add_interrupt_randomness(), unlike its counterpart
handle_percpu_irq().

Cleanup this somewhat confusing situation by doing the
add_interrupt_randomness() in handle_percpu_devid_irq(), and remove
it from the Hyper-V ISRs. Then only the Hyper-V custom sysvec path,
which plays the role of a generic interrupt handler, needs to do
add_interrupt_randomness(). As a result of this change, no
device drivers are calling add_interrupt_randomness(), which is
appropriate.

The change is broken into two patches since it spans generic
interrupt handling code and Hyper-V specific code. But the two
patches should be taken together through the same tree. It's
OK to have a bisect window where add_interrupt_randomness() is
done in both places, but taking the Hyper-V patch first could leave
a bisect window where add_interrupt_randomness() is not done in
either place.

Michael Kelley (2):
  genirq/chip: Do add_interrupt_randomness() in
    handle_percpu_devid_irq()
  Drivers: hv: Move add_interrupt_randomness() to hypervisor callback
    sysvec

 arch/x86/kernel/cpu/mshyperv.c | 2 ++
 drivers/hv/mshv_synic.c        | 3 ---
 drivers/hv/vmbus_drv.c         | 3 ---
 kernel/irq/chip.c              | 3 +++
 4 files changed, 5 insertions(+), 6 deletions(-)

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2.25.1