From: "Woodhouse, David" <dwmw@amazon.co.uk>
To: Jim Mattson <jmattson@google.com>,
"Hussain, Mushahid" <hmushi@amazon.co.uk>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
"K . Y . Srinivasan" <kys@microsoft.com>,
"Haiyang Zhang" <haiyangz@microsoft.com>,
Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
Long Li <longli@microsoft.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"nh-open-source@amazon.com" <nh-open-source@amazon.com>,
"mushi.shar@gmail.com" <mushi.shar@gmail.com>,
Todd Frederick <tfred@google.com>
Subject: Re: [PATCH 3/3] KVM: x86: hyper-v: Implement HvCallRestorePartitionTime
Date: Tue, 13 Oct 2026 11:32:55 +0000 [thread overview]
Message-ID: <23274a3d540e4bc36a88262c06adc7b16eaa7a3f.camel@amazon.co.uk> (raw)
In-Reply-To: <CALMp9eQz2ouQvFhBYv_R33_sUQ+ehxv__-f5iZ=_3aA2Guwy5w@mail.gmail.com>
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On Mon, 2026-10-12 at 14:23 -0700, Jim Mattson wrote:
>
> I think there's a window here in which another vCPU can consume
> HV_TSC_PAGE_GUEST_CHANGED before kvm_set_clock_and_tsc() steps the
> clocks. If TSC emulation control is enabled,
> kvm_hv_request_tsc_page_update() won't invalidate the resulting stale
> TSC page.
>
> > + kvm_set_clock_and_tsc(vcpu->kvm, in.reference_time_in_100ns * 100, in.tsc);
>
> When stepping the reference time forward, don't we have to recalculate
> the hrtimer deadlines associated with armed synthetic timers?
> Otherwise, those hrtimers will fire late.
My understanding is that Windows only does this at resume time when
nothing else is running, so it doesn't matter much.
Either way, I don't think we want *any* of this in the kernel; we
should just pass the hypercall up to userspace and let userspace handle
it.
There's a commit somewhere in
https://git.infradead.org/?p=users/dwmw2/linux.git;a=shortlog;h=refs/heads/vsm
which does that; I'm working on cleaning that lot up to be postable
this week. (s/linux/kvm-unit-tests/ and s/linux/qemu/ for the other
parts, if you want an early preview that actually boots Windows guests
under KVM with VSM support).
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Amazon Development Centre (London) Ltd. Registered in England and Wales with registration number 04543232 with its registered office at 1 Principal Place, Worship Street, London EC2A 2FA, United Kingdom.
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next prev parent reply other threads:[~2026-10-13 11:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-05 19:24 [PATCH 0/3] KVM: x86: Support hibernation of a nested Hyper-V Mushahid Hussain
2026-10-05 19:24 ` [PATCH 1/3] KVM: nVMX: Clear stale vmcs02 sync flag in free_nested() Mushahid Hussain
2026-10-12 19:29 ` Jim Mattson
2026-10-05 19:24 ` [PATCH 2/3] KVM: x86: Extract __kvm_set_clock() from kvm_vm_ioctl_set_clock() Mushahid Hussain
2026-10-12 19:35 ` Jim Mattson
2026-10-05 19:24 ` [PATCH 3/3] KVM: x86: hyper-v: Implement HvCallRestorePartitionTime Mushahid Hussain
2026-10-05 22:30 ` David Woodhouse
2026-10-12 21:23 ` Jim Mattson
2026-10-13 11:32 ` Woodhouse, David [this message]
2026-10-06 5:08 ` [PATCH 0/3] KVM: x86: Support hibernation of a nested Hyper-V David Woodhouse
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