linux-kernel - Re: [PATCH v2] clocksource: hyper-v: Use lapic timer in a TDX VM without paravisor

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Date: Mon, 24 Jun 2024 07:06:50 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Dexuan Cui <decui@...rosoft.com>
Cc: mhklinux@...look.com, "K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"open list:Hyper-V/Azure CORE AND DRIVERS" <linux-hyperv@...r.kernel.org>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org, Roman Kisel <romank@...ux.microsoft.com>
Subject: Re: [PATCH v2] clocksource: hyper-v: Use lapic timer in a TDX VM
 without paravisor

On Thu, Jun 20, 2024 at 11:16:14PM -0700, Dexuan Cui wrote:
> In a TDX VM without paravisor, currently the default timer is the Hyper-V
> timer, which depends on the slow VM Reference Counter MSR: the Hyper-V TSC
> page is not enabled in such a VM because the VM uses Invariant TSC as a
> better clocksource and it's challenging to mark the Hyper-V TSC page shared
> in very early boot.
> 
> Lower the rating of the Hyper-V timer so the local APIC timer becomes the
> the default timer in such a VM, and print a warning in case Invariant TSC
> is unavailable in such a VM. This change should cause no perceivable
> performance difference.
> 
> Cc: stable@...r.kernel.org # 6.6+
> Reviewed-by: Roman Kisel <romank@...ux.microsoft.com>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>

Applied to hyperv-fixes. Thanks.