xen/arch/x86/time.c: Bug fix - Integer overflow when cpu frequency > u32 max
value.
What is was trying to do: I was trying to install QubesOS on my new computer
(AMD zen4 processor). Guest VM were unusably slow / unusable.
What is the issue: The cpu frequency reported is wrong for linux guest in HVM
and PVH mode, and it cause issue with the TSC clocksource (for example).
Why this patch solved my issue:
The root cause it that "d->arch.tsc_khz" is a unsigned integer storing
the cpu frequency in khz. It get multiplied by 1000, so if the cpu frequency
is over ~4,294 Mhz (u32 max value), then it overflow.
I am solving the issue by adding an explicit cast to u64 to avoid the overflow.
---
xen/arch/x86/time.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index b01acd390d..7c77ec8902 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -2585,7 +2585,7 @@ int tsc_set_info(struct domain *d,
case TSC_MODE_ALWAYS_EMULATE:
d->arch.vtsc_offset = get_s_time() - elapsed_nsec;
d->arch.tsc_khz = gtsc_khz ?: cpu_khz;
- set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000);
+ set_time_scale(&d->arch.vtsc_to_ns, (u64)d->arch.tsc_khz * 1000);
/*
* In default mode use native TSC if the host has safe TSC and
--
2.38.1
