arm64: KVM: VHE: reset PSTATE.PAN on entry to EL2

commit cb96408d upstream.

SCTLR_EL2.SPAN bit controls what happens with the PSTATE.PAN bit on an
exception. However, this bit has no effect on the PSTATE.PAN when
HCR_EL2.E2H or HCR_EL2.TGE is unset. Thus when VHE is used and
exception taken from a guest PSTATE.PAN bit left unchanged and we
continue with a value guest has set.

To address that always reset PSTATE.PAN on entry from EL1.

Fixes: 1f364c8c ("arm64: VHE: Add support for running Linux in EL2 mode")
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
[ rebased for v4.7+ ]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/kvm/hyp/entry.S

@@ -98,6 +98,8 @@ ENTRY(__guest_exit)
 	// x4-x29,lr: vcpu regs
 	// vcpu x0-x3 on the stack
 
+	ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)
+
 	add	x2, x0, #VCPU_CONTEXT
 
 	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]