linux-kernel - Re: [PATCH hyperv-next 0/2] x86/hyperv: VTL mode reboot fixes

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Message-ID: <20250213105232.GA32701@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Thu, 13 Feb 2025 02:52:32 -0800
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: Wei Liu <wei.liu@...nel.org>, bp@...en8.de, dave.hansen@...ux.intel.com,
	decui@...rosoft.com, haiyangz@...rosoft.com, hpa@...or.com,
	kys@...rosoft.com, mingo@...hat.com, tglx@...utronix.de,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, apais@...rosoft.com, benhill@...rosoft.com,
	sunilmut@...rosoft.com, vdso@...bites.dev
Subject: Re: [PATCH hyperv-next 0/2] x86/hyperv: VTL mode reboot fixes

On Wed, Feb 12, 2025 at 02:56:43PM -0800, Roman Kisel wrote:
> 
> 
> On 2/12/2025 9:54 AM, Saurabh Singh Sengar wrote:
> >On Wed, Feb 12, 2025 at 02:21:18AM +0000, Wei Liu wrote:
> [...]
> >>
> >>Saurabh please review these patches. Thanks.
> >
> >Hi Roman,
> Hi Saurabh,
> 
> >
> >Thanks for the patch, few suggestions and queries:
> >
> >1. Please fix the kernel bot warning
> Will do!
> 
> >2. Cc Stable tree is not enough, you need to mention the "Fixes" tag as well
> >    for the commit upto where you want this patch to be backported.
> Understood, thanks!
> 
> >3. In your 2/2 commit, you mention 'triple fault' is the only way to reboot in x86.
> >    Is that accurate ? Do you mean to say OpenHCL/VTL here ?
> >    If this behaviour is specific to OpenHCl and not VTLs in general, is there a way
> >    we can make these changes only for OpenHCL.
> Right, I meant OpenHCL/VTL2, thank you very much! The changes are scoped
> to running in VTLs in general at the moment. I can add a check for the
> VTL == 2 if you'd like me to.
> 
> For VTL1 (aka LVBS), maybe folks would like to do something else,
> do you happen to know? Maybe to report that to the VTL0 guest kernel
> although seems dubious: the higher VTL failed so the lights must be out
> for the lower VTLs? Or kexec?

I am not aware of LVBS plans, and as far as I consider OpenVMM the only current
user of this VTL code. I recommend keeping the code as simple as possible unless
there is a clear use case for additional complexity. It would be helpful to include
these details in a comment so that future users of this file can understand and
modify it as needed.

- Saurabh

> 
> >
> >- Saurabh
> >
> >>
> >>I don't have a strong opinion on them.
> >>
> >>>
> >>>  arch/x86/hyperv/hv_vtl.c | 31 +++++++++++++++++++++++++++++++
> >>>  1 file changed, 31 insertions(+)
> >>>
> >>>
> >>>base-commit: 2e03358be78b65d28b66e17aca9e0c8700b0df78
> >>>-- 
> >>>2.34.1
> >>>
> 
> -- 
> Thank you,
> Roman
>