Peter Maydell, thank you for your comments. I apologize for so late response - returned to this issue and now I will answer faster. I fixed the commit according to your recommendations, please take a look at the new version.
> There is also a comment or two from me in the bug report pointing > out that the handling of wraparound is also wrong in the other > half of this if(); we should look at that too. I read this topic and as I understand changing the other half of "if" is not related to the reported issue. Since it affects running virtualized setups on arm64 QEMU, e.g. Zephyr (https://github.com/zephyrproject-rtos/zephyr/blob/main//boards/arm64/xenvm/doc/index.rst) maybe is it worth merging at least this change? Best regards, Leonid Komarianskyi. On 09.11.23 15:55, Leonid Komarianskyi wrote: > If gt_timer is enabled before cval initialization on a virtualized > setup on QEMU, cval equals (UINT64_MAX - 1). Adding an offset value > to this causes an overflow that sets timer into the past, which leads > to infinite loop, because this timer fires immediately and calls > gt_recalc_timer() once more, which in turn sets the timer into the > past again and as a result, QEMU hangs. This patch adds check for > overflowing of the nexttick variable. > > Suggested-by: Volodymyr Babchuk <volodymyr_babc...@epam.com> > Co-Authored-By: Dmytro Firsov <dmytro_fir...@epam.com> > Signed-off-by: Leonid Komarianskyi <leonid_komarians...@epam.com> > --- > target/arm/helper.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/target/arm/helper.c b/target/arm/helper.c > index 3b22596eab..b4aaa2965b 100644 > --- a/target/arm/helper.c > +++ b/target/arm/helper.c > @@ -2665,6 +2665,16 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx) > } else { > /* Next transition is when we hit cval */ > nexttick = gt->cval + offset; > + if (nexttick < gt->cval) { > + /* > + * If gt->cval value is close to UINT64_MAX then adding > + * to it offset can lead to overflow of nexttick variable. > + * So, this check tests that arguments sum is less than any > + * addend, and in case it is overflowed we have to mod timer > + * to INT64_MAX. > + */ > + nexttick = UINT64_MAX; > + } > } > /* > * Note that the desired next expiry time might be beyond the
