linux-kernel - Re: [PATCH v1 1/1] s390/protvirt: fix compilation issue

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Date:   Thu, 23 Apr 2020 14:54:22 +0200
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, borntraeger@...ibm.com,
        frankja@...ux.ibm.com, cohuck@...hat.com, david@...hat.com,
        kbuild test robot <lkp@...el.com>,
        Philipp Rudo <prudo@...ux.ibm.com>
Subject: Re: [PATCH v1 1/1] s390/protvirt: fix compilation issue

On Thu, Apr 23, 2020 at 02:01:14PM +0200, Claudio Imbrenda wrote:
> The kernel fails to compile with CONFIG_PROTECTED_VIRTUALIZATION_GUEST
> set but CONFIG_KVM unset.
> 
> This patch fixes the issue by making the needed variable always available.

This statement confuses me a bit.

It's worth to mention that both arch/s390/boot/uv.c (for the
decompressor) and arch/s390/kernel/uv.c (for the main kernel) are only
built when either CONFIG_PROTECTED_VIRTUALIZATION_GUEST or
CONFIG_KVM is enabled.
Both arch/s390/boot/Makefile and arch/s390/kernel/Makefile contain:
obj-$(findstring y, $(CONFIG_PROTECTED_VIRTUALIZATION_GUEST) $(CONFIG_PGSTE))   += uv.o

So this makes the variable available when
CONFIG_PROTECTED_VIRTUALIZATION_GUEST or CONFIG_KVM (expressed via
CONFIG_PGSTE) is enabled. Hence no need for extra conditions for variable
declaration.

> Fixes: a0f60f8431999bf5 ("s390/protvirt: Add sysfs firmware interface for Ultravisor information")
> Reported-by: kbuild test robot <lkp@...el.com>
> Reported-by: Philipp Rudo <prudo@...ux.ibm.com>
> Suggested-by: Philipp Rudo <prudo@...ux.ibm.com>
> CC: Vasily Gorbik <gor@...ux.ibm.com>
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>  arch/s390/boot/uv.c   | 2 --
>  arch/s390/kernel/uv.c | 3 ++-
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/boot/uv.c b/arch/s390/boot/uv.c
> index 8fde561f1d07..f887a479cdc7 100644
> --- a/arch/s390/boot/uv.c
> +++ b/arch/s390/boot/uv.c
> @@ -7,9 +7,7 @@
>  #ifdef CONFIG_PROTECTED_VIRTUALIZATION_GUEST
>  int __bootdata_preserved(prot_virt_guest);
>  #endif
> -#if IS_ENABLED(CONFIG_KVM)
>  struct uv_info __bootdata_preserved(uv_info);
> -#endif
>  
>  void uv_query_info(void)
>  {
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index c86d654351d1..4c0677fc8904 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -23,10 +23,11 @@
>  int __bootdata_preserved(prot_virt_guest);
>  #endif
>  
> +struct uv_info __bootdata_preserved(uv_info);
> +
>  #if IS_ENABLED(CONFIG_KVM)
>  int prot_virt_host;
>  EXPORT_SYMBOL(prot_virt_host);
> -struct uv_info __bootdata_preserved(uv_info);
>  EXPORT_SYMBOL(uv_info);

hm, EXPORT_SYMBOL(uv_info) is not needed without CONFIG_KVM and this saves
1 symbol export, but I'd still made EXPORT_SYMBOL follow the declaration
immediately. Documentation/process/coding-style.rst mentions that only
for function declarations though.

Reviewed-by: Vasily Gorbik <gor@...ux.ibm.com>