qemu-system-aarch64 (tcg): cval + voff overflow not handled, causes qemu to hang

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1859021

The Armv8 architecture reference manual states that for any timer set
(e.g. CNTP* and CNTV*), the condition for such timer to generate an
interrupt (if enabled & unmasked) is:

CVAL <= CNT(P/V)CT

Although this is arguably sloppy coding, I have seen code that is
therefore assuming it can set CVAL to a very high value (e.g. UINT64_MAX)
and leave the interrupt enabled in CTL, and never get the interrupt.

On latest master commit as the time of writing, there is an integer
overflow in target/arm/helper.c gt_recalc_timer affecting the virtual
timer when the interrupt is enabled in CTL:

    /* Next transition is when we hit cval */
    nexttick = gt->cval + offset;

When this overflow happens, I notice that qemu is no longer responsive and
that I have to SIGKILL the process:
    - qemu takes nearly all the cpu time of the cores it is running on
(e.g. 50% cpu usage if running on half the cores) and is completely
unresponsive
    - no guest interrupt (reported via -d int) is generated

Here the minimal code example to reproduce the issue:

    mov     x0, #1
    msr     cntvoff_el2, x0
    mov     x0, #-1
    msr     cntv_cval_el0, x0
    mov     x0, #1
    msr     cntv_ctl_el0, x0 // interrupt generation enabled, not masked;
qemu will start to hang here

Options used:
-nographic -machine virt,virtualization=on,gic-version=2,accel=tcg -cpu
cortex-a57
-smp 4 -m 1024 -kernel whatever.elf -d unimp,guest_errors,int
-semihosting-config enable,target=native
-serial mon:stdio

Version used: 4.2