linux-kernel - [PATCH] hv: add CONFIG

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Message-ID: <20250610153354.2780-1-romank@linux.microsoft.com>
Date: Tue, 10 Jun 2025 08:33:54 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: arnd@...nel.org
Cc: arnd@...db.de,
	decui@...rosoft.com,
	haiyangz@...rosoft.com,
	kys@...rosoft.com,
	linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	mhklinux@...look.com,
	nunodasneves@...ux.microsoft.com,
	romank@...ux.microsoft.com,
	ssengar@...ux.microsoft.com,
	wei.liu@...nel.org
Subject: [PATCH] hv: add CONFIG_EFI dependency

> Selecting SYSFB causes a link failure on arm64 kernels with EFI disabled:
>
> ld.lld-21: error: undefined symbol: screen_info
> >>> referenced by sysfb.c
> >>>               drivers/firmware/sysfb.o:(sysfb_parent_dev) in archive vmlinux.a
> >>> referenced by sysfb.c
>
> The problem is that sysfb works on the global 'screen_info' structure, which
> is provided by the firmware interface, either the generic EFI code or the
> x86 BIOS startup.
>
> Assuming that HV always boots Linux using UEFI, the dependency also makes
> logical sense, since otherwise it is impossible to boot a guest.
>

Hyper-V as of recent can boot off DeviceTree with the direct kernel boot, no UEFI
is required (examples would be OpenVMM and the OpenHCL paravisor on arm64).

Being no expert in Kconfig unfortunately... If another solution is possible to
find given the timing constraints (link errors can't wait iiuc) that would be
great :)

Could something like "select EFI if SYSFB" work?

> Fixes: 96959283a58d ("Drivers: hv: Always select CONFIG_SYSFB for Hyper-V guests")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/hv/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 8622d0733723..07db5e9a00f9 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -6,6 +6,7 @@ config HYPERV
>  	tristate "Microsoft Hyper-V client drivers"
>  	depends on (X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
>  		|| (ARM64 && !CPU_BIG_ENDIAN && HAVE_ARM_SMCCC_DISCOVERY)
> +	depends on EFI
>  	select PARAVIRT
>  	select X86_HV_CALLBACK_VECTOR if X86
>  	select OF_EARLY_FLATTREE if OF
> --
> 2.39.5