tree 16c0697307e1853cee7f72e10876f35d6b25b252
parent ac031a0d05f40a5ec78e58ba7406d8748f6c1382
author Marc Zyngier <maz@kernel.org> 1579074767 +0100
committer Marc Zyngier <maz@kernel.org> 1581440472 +0000

KVM: arm64: nv: Fast-track 'InHost' exception returns

A significant part of the ARMv8.3-NV extension is to trap ERET
instructions so that the hypervisor gets a chance to switch
from a vEL2 L1 guest to an EL1 L2 guest.

But this also has the unfortunate consequence of trapping ERET
in unsuspecting circumstances, such as staying at vEL2 (interrupt
handling while being in the guest hypervisor), or returning to host
userspace in the case of a VHE guest.

Although we already make some effort to handle these ERET quicker
by not doing the put/load dance, it is still way too far down the
line for it to be efficient enough.

For these cases, it would ideal to ERET directly, no question asked.
Of course, we can't do that. But the next best thing is to do it as
early as possible, in fixup_guest_exit(), much as we would handle
FPSIMD exceptions.

Signed-off-by: Marc Zyngier <maz@kernel.org>