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

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Message-ID: <20250212175445.GA19243@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Wed, 12 Feb 2025 09:54:45 -0800
From: Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
To: Wei Liu <wei.liu@...nel.org>
Cc: Roman Kisel <romank@...ux.microsoft.com>, 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 02:21:18AM +0000, Wei Liu wrote:
> On Fri, Jan 17, 2025 at 01:07:00PM -0800, Roman Kisel wrote:
> > The first patch defines a specialized machine emergency restart
> > callback not to write to the physical address of 0x472 which is
> > what the native_machine_emergency_restart() does unconditionally.
> > 
> > I first wanted to tweak that function[1], and in the course of
> > the discussion it looked as the risks of doing that would
> > outweigh the benefit: the bare-metal systems have likely adopted
> > that behavior as a standard although I could not find any mentions
> > of that magic address in the UEFI+ACPI specification.
> > 
> > The second patch removes the need to always supply "reboot=t"
> > to the kernel command line in the OpenHCL bootloader [2]. There is
> > no other option at the moment; when/if it appears the newly added
> > callback's code can be adjusted as required.
> > 
> > It would be great to apply this to the stable tree if no concerns,
> > should apply cleanly.
> > 
> > [1] https://lore.kernel.org/all/20250109204352.1720337-1-romank@linux.microsoft.com/
> > [2] https://github.com/microsoft/openvmm/blob/7a9d0e0a00461be6e5f3267af9ea54cc7157c900/openhcl/openhcl_boot/src/main.rs#L139
> > 
> > Roman Kisel (2):
> >   x86/hyperv: VTL mode emergency restart callback
> >   x86/hyperv: VTL mode callback for restarting the system
> 
> Saurabh please review these patches. Thanks.

Hi Roman,

Thanks for the patch, few suggestions and queries:

1. Please fix the kernel bot warning
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.
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.
   

- 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
> >