linux-kernel - Re: [PATCH] mshv: hide x86-specific functions on arm64

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Message-ID: <20251218191523.GB1749918@liuwe-devbox-debian-v2.local>
Date: Thu, 18 Dec 2025 19:15:23 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>
Cc: Wei Liu <wei.liu@...nel.org>, Arnd Bergmann <arnd@...nel.org>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Dexuan Cui <decui@...rosoft.com>, Long Li <longli@...rosoft.com>,
	Stansialv Kinsburskii <skinsburskii@...ux.miscrosoft.com>,
	Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
	Praveen K Paladugu <prapal@...ux.microsoft.com>,
	Easwar Hariharan <easwar.hariharan@...ux.microsoft.com>,
	Anatol Belski <anbelski@...ux.microsoft.com>,
	Arnd Bergmann <arnd@...db.de>,
	Sean Christopherson <seanjc@...gle.com>,
	Naman Jain <namjain@...ux.microsoft.com>,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mshv: hide x86-specific functions on arm64

On Tue, Dec 16, 2025 at 04:45:12PM -0800, Stanislav Kinsburskii wrote:
> On Tue, Dec 16, 2025 at 10:21:29PM +0000, Wei Liu wrote:
> > On Tue, Dec 16, 2025 at 10:36:12PM +0100, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@...db.de>
> > > 
> > > The hv_sleep_notifiers_register() and hv_machine_power_off() functions are
> > > only called and declared on x86, but cause a warning on arm64:
> > > 
> > > drivers/hv/mshv_common.c:210:6: error: no previous prototype for 'hv_sleep_notifiers_register' [-Werror=missing-prototypes]
> > >   210 | void hv_sleep_notifiers_register(void)
> > >       |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > drivers/hv/mshv_common.c:224:6: error: no previous prototype for 'hv_machine_power_off' [-Werror=missing-prototypes]
> > >   224 | void hv_machine_power_off(void)
> > >       |      ^~~~~~~~~~~~~~~~~~~~
> > > 
> > > Hide both inside of an #ifdef block.
> > > 
> > > Fixes: f0be2600ac55 ("mshv: Use reboot notifier to configure sleep state")
> > > Fixes: 615a6e7d83f9 ("mshv: Cleanly shutdown root partition with MSHV")
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > 
> > Thanks Arnd. I have a queued up a patch which make available the
> > declarations to arm64. Let me think about whether to use your patch
> > instead.
> > 
> > Anyway, this issue will be fixed one way or the other once I send a PR
> > to Linus.
> > 
> 
> The whole idea of mshv_common.c is to have common code for all archs.
> It would be nice to keep this file as it is.

The path forward is either to move these functions to an x86-specific
file or to make arm64 work the same way. I'm not too sure about the
latter yet given the port is yet to be done. For the time being, I am
going to drop my own patch and take Arnd's patch. We can figure out
which of the two approaches to take later.

Wei