linux-kernel - Re: [PATCH v3] x86/hyperv: Use per cpu initial stack for vtl context

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Message-ID: <ZeZmysa1x4dogjQs@liuwe-devbox-debian-v2>
Date: Tue, 5 Mar 2024 00:26:50 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
Cc: Wei Liu <wei.liu@...nel.org>, kys@...rosoft.com, haiyangz@...rosoft.com,
	decui@...rosoft.com, tglx@...utronix.de, mingo@...hat.com,
	bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
	hpa@...or.com, dwmw@...zon.co.uk, peterz@...radead.org,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	ssengar@...rosoft.com, mhklinux@...look.com
Subject: Re: [PATCH v3] x86/hyperv: Use per cpu initial stack for vtl context

On Sun, Mar 03, 2024 at 11:08:17PM -0800, Saurabh Singh Sengar wrote:
> On Mon, Mar 04, 2024 at 06:24:27AM +0000, Wei Liu wrote:
> > On Sun, Mar 03, 2024 at 12:01:36AM -0800, Saurabh Sengar wrote:
> > > Currently, the secondary CPUs in Hyper-V VTL context lack support for
> > > parallel startup. Therefore, relying on the single initial_stack fetched
> > > from the current task structure suffices for all vCPUs.
> > > 
> > > However, common initial_stack risks stack corruption when parallel startup
> > > is enabled. In order to facilitate parallel startup, use the initial_stack
> > > from the per CPU idle thread instead of the current task.
> > > 
> > > Fixes: 18415f33e2ac ("cpu/hotplug: Allow "parallel" bringup up to CPUHP_BP_KICK_AP_STATE")
> > 
> > I don't think this patch is buggy. Instead, it exposes an assumption in
> > the VTL code. So this either should be dropped or point to the patch
> > which introduces the assumption.
> > 
> > Let me know what you would prefer.
> 
> The VTL code will crash if this fix is not present post above mentioned patch:
> 18415f33e2ac ("cpu/hotplug: Allow "parallel" bringup up to CPUHP_BP_KICK_AP_STATE").
> So I would prefer a fixes which added the assumption in VTL:
> 
> Fixes: 3be1bc2fe9d2 ("x86/hyperv: VTL support for Hyper-V")
> 
> Please let me know if you need V4 for it.

No need to repost. I can change the commit message.

Thanks,
Wei.