arm64: kvm: report original PAR_EL1 upon panic

If we call __kvm_hyp_panic while a guest context is active, we call
__restore_sysregs before acquiring the system register values for the
panic, in the process throwing away the PAR_EL1 value at the point of
the panic.

This patch modifies __kvm_hyp_panic to stash the PAR_EL1 value prior to
restoring host register values, enabling us to report the original
values at the point of the panic.
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NChristoffer Dall <christoffer.dall@linaro.org>

arch/arm64/kvm/hyp.S

@@ -864,6 +864,10 @@ ENTRY(__kvm_flush_vm_context)
 ENDPROC(__kvm_flush_vm_context)
 
 __kvm_hyp_panic:
+	// Stash PAR_EL1 before corrupting it in __restore_sysregs
+	mrs	x0, par_el1
+	push	x0, xzr
+
 	// Guess the context by looking at VTTBR:
 	// If zero, then we're already a host.
 	// Otherwise restore a minimal host context before panicing.
@@ -898,7 +902,7 @@ __kvm_hyp_panic:
 	mrs	x3, esr_el2
 	mrs	x4, far_el2
 	mrs	x5, hpfar_el2
-	mrs	x6, par_el1
+	pop	x6, xzr		// active context PAR_EL1
 	mrs	x7, tpidr_el2
 
 	mov	lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\