On 29/07/2017 14:35, Denis Plotnikov wrote:
> Now, L2 guests can't have a stable kvmclock while working over L1 with
> a stable kvmclock. It is so just because of lack of functionality.
>
> The patch is a part of work making kvmclock stable in L2 if it works
> over a stable kvmclock.
>
> Signed-off-by: Denis Plotnikov <dplotnikov@xxxxxxxxxxxxx>
> ---
> arch/x86/kernel/pvclock.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
> index a2c554a..5b0bb2e 100644
> --- a/arch/x86/kernel/pvclock.c
> +++ b/arch/x86/kernel/pvclock.c
> @@ -22,6 +22,7 @@
> #include <linux/gfp.h>
> #include <linux/bootmem.h>
> #include <linux/nmi.h>
> +#include <linux/cs_notifier.h>
>
> #include <asm/fixmap.h>
> #include <asm/pvclock.h>
> @@ -73,6 +74,8 @@ u8 pvclock_read_flags(struct pvclock_vcpu_time_info *src)
> return flags & valid_flags;
> }
>
> +static atomic64_t clocksource_stable = ATOMIC64_INIT(0);
No need for atomic64. Otherwise looks good.
Paolo
> u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src, u64 *cycles)
> {
> unsigned version;
> @@ -96,10 +99,20 @@ u64 pvclock_clocksource_read(struct pvclock_vcpu_time_info *src, u64 *cycles)
> pvclock_touch_watchdogs();
> }
>
> - if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
> - (flags & PVCLOCK_TSC_STABLE_BIT))
> - return ret;
> + if (likely(valid_flags & PVCLOCK_TSC_STABLE_BIT)) {
> + bool stable_now = !!(flags & PVCLOCK_TSC_STABLE_BIT);
> + bool stable_last = (bool) atomic64_read(&clocksource_stable);
> +
> + if (unlikely(stable_now != stable_last)) {
> + /* send notification once */
> + if (stable_last == atomic64_cmpxchg(
> + &clocksource_stable, stable_last, stable_now))
> + clocksource_changes_notify();
> + }
>
> + if (stable_now)
> + return ret;
> + }
> /*
> * Assumption here is that last_value, a global accumulator, always goes
> * forward. If we are less than that, we should not be much smaller.
>
