Re: [RFC PATCH 0/6] x86/kvm: Virtual suspend time injection support

From: Maxim Levitsky
Date: Mon Apr 26 2021 - 09:16:19 EST


On Mon, 2021-04-26 at 18:06 +0900, Hikaru Nishida wrote:
> Hi,
>
> This patch series adds virtual suspend time injection support to KVM.
>
> Before this change, if the host goes into suspended state while the
> guest is running, the guest will experience a time jump after the host's
> resume. This can confuse some services in the guest since they can't
> detect if the system went into suspend or not by comparing
> CLOCK_BOOTTIME and CLOCK_MONOTONIC.
>
> To solve this problem, we wanted to add a way to adjust the guest clocks
> without actually suspending the guests. However, there was no way to
> modify a gap between CLOCK_BOOTTIME and CLOCK_MONOTONIC without actually
> suspending the guests. Therefore, this series introduce a new struct
> called kvm_host_suspend_time to share the suspend time between host and
> guest and a mechanism to inject a suspend time to the guest while
> keeping
> monotonicity of the clocks.
>
> Could you take a look and let me know how we can improve the patches if
> they are doing something wrong?
>
> Thanks,
>
> Hikaru Nishida
>

I haven't yet looked at that, but in my experience when I suspend the host
with VMs running, after resume all my VMs complain something about TSC watchdog
and stop using it. The TSC is stable/synchornized, but after resume it does
reset to 0 on all CPUs.

I use INVTSC flag for all my VMs.
I haven't investigated this futher yet.

Just my 0.2 cents.

Best regards,
Maxim Levitsky

>
>
> Hikaru Nishida (6):
> x86/kvm: Reserve KVM_FEATURE_HOST_SUSPEND_TIME and
> MSR_KVM_HOST_SUSPEND_TIME
> x86/kvm: Add a struct and constants for virtual suspend time injection
> x86/kvm: Add CONFIG_KVM_VIRT_SUSPEND_TIMING
> x86/kvm: Add a host side support for virtual suspend time injection
> x86/kvm: Add CONFIG_KVM_VIRT_SUSPEND_TIMING_GUEST
> x86/kvm: Add a guest side support for virtual suspend time injection
>
> Documentation/virt/kvm/cpuid.rst | 3 +
> Documentation/virt/kvm/msr.rst | 29 +++++++++
> arch/x86/Kconfig | 13 ++++
> arch/x86/include/asm/kvm_host.h | 5 ++
> arch/x86/include/asm/kvm_para.h | 9 +++
> arch/x86/include/uapi/asm/kvm_para.h | 6 ++
> arch/x86/kernel/kvmclock.c | 25 ++++++++
> arch/x86/kvm/Kconfig | 13 ++++
> arch/x86/kvm/cpuid.c | 4 ++
> arch/x86/kvm/x86.c | 89 +++++++++++++++++++++++++++-
> include/linux/kvm_host.h | 7 +++
> include/linux/timekeeper_internal.h | 4 ++
> kernel/time/timekeeping.c | 31 ++++++++++
> 13 files changed, 237 insertions(+), 1 deletion(-)
>