kvm: arm64: vgic: fix hyp panic with 64k pages on juno platform

If the physical address of GICV isn't page-aligned, then we end up
creating a stage-2 mapping of the page containing it, which causes us to
map neighbouring memory locations directly into the guest.

As an example, consider a platform with GICV at physical 0x2c02f000
running a 64k-page host kernel. If qemu maps this into the guest at
0x80010000, then guest physical addresses 0x80010000 - 0x8001efff will
map host physical region 0x2c020000 - 0x2c02efff. Accesses to these
physical regions may cause UNPREDICTABLE behaviour, for example, on the
Juno platform this will cause an SError exception to EL3, which brings
down the entire physical CPU resulting in RCU stalls / HYP panics / host
crashing / wasted weeks of debugging.

SBSA recommends that systems alias the 4k GICV across the bounding 64k
region, in which case GICV physical could be described as 0x2c020000 in
the above scenario.

This patch fixes the problem by failing the vgic probe if the physical
base address or the size of GICV aren't page-aligned. Note that this
generated a warning in dmesg about freeing enabled IRQs, so I had to
move the IRQ enabling later in the probe.

Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Joel Schopp <joel.schopp@amd.com>
Cc: Don Dutile <ddutile@redhat.com>
Acked-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Joel Schopp <joel.schopp@amd.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>