ARMv8-A: Virtual to physical translation sometime "fails"

Hi

I have a strange effect: I need to convert a virtual address to the physical one.

In the current scenario, I have a 1:1 mapping, so I would not need it, but left the code:

	mov	x3,x0  // for debug
	at	S1E1W,x0
	isb
	mrs	x1,PAR_EL1
	mov	x4,x1 // for debug
	tst	x1,#1
	bfi	x1,x0,#0,#12
	bic	x0,x1,#0xff00000000000000
	mov	x2,#SC_NIL & 0xffff
	movk	x2,#(SC_NIL>>16) & 0xffff,lsl #16
	csel	x0,x0,x2,EQ	// on error return SC_NIL
1:
	cmp	x3,x0
	b.ne	1b
	ret

This code works w/o problem, but under heavy interrupt load, I get a wrong value in PAR_EL1. Since the 1:1 mapping the final result should be the input parameter.

I have no idea what is going wrong. The MMU is only setup on boot and no more changes are applied neither to the pagetable nor the ASID.

The code runs in 64bit mode in EL1.

Any hint?