Re: [tip: x86/percpu] x86/percpu: Declare const_pcpu_hot as extern const variable

[Borislav Petkov]

On Thu, Nov 30, 2023 at 09:16:30PM -0000, tip-bot2 for Uros Bizjak wrote:
> The following commit has been merged into the x86/percpu branch of tip:
> 
> Commit-ID:     4604c052b84d66407f5e68045a1939685eac401e
> Gitweb:        https://git.kernel.org/tip/4604c052b84d66407f5e68045a1939685eac401e
> Author:        Uros Bizjak <ubizjak@xxxxxxxxx>
> AuthorDate:    Thu, 30 Nov 2023 17:27:35 +01:00
> Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
> CommitterDate: Thu, 30 Nov 2023 20:19:33 +01:00
> 
> x86/percpu: Declare const_pcpu_hot as extern const variable
> 
> const_pcpu_hot is aliased by linker to pcpu_hot, so there is no need
> to use the DECLARE_PER_CPU_ALIGNED() macro. Also, declare const_pcpu_hot
> as extern to avoid allocating storage space for the aliased structure.
> 
> Fixes: ed2f752e0e0a ("x86/percpu: Introduce const-qualified const_pcpu_hot to micro-optimize code generation")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20231130162949.83518-1-ubizjak@xxxxxxxxx
> Closes: https://lore.kernel.org/oe-kbuild-all/202311302257.tSFtZnly-lkp@xxxxxxxxx/
> ---
>  arch/x86/include/asm/current.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h
> index 0538d24..9fbd7cb 100644
> --- a/arch/x86/include/asm/current.h
> +++ b/arch/x86/include/asm/current.h
> @@ -37,8 +37,7 @@ static_assert(sizeof(struct pcpu_hot) == 64);
>  DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
>  
>  /* const-qualified alias to pcpu_hot, aliased by linker. */
> -DECLARE_PER_CPU_ALIGNED(const struct pcpu_hot __percpu_seg_override,
> -			const_pcpu_hot);
> +extern const struct pcpu_hot __percpu_seg_override const_pcpu_hot;
>  
>  static __always_inline struct task_struct *get_current(void)
>  {

WARNING: modpost: EXPORT symbol "const_pcpu_hot" [vmlinux] version generation failed, symbol will not be versioned.
Is "const_pcpu_hot" prototyped in <asm/asm-prototypes.h>?
WARNING: modpost: "const_pcpu_hot" [arch/x86/kvm/kvm.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [arch/x86/kvm/kvm-intel.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [kernel/trace/preemptirq_delay_test.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [fs/exfat/exfat.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [fs/ntfs/ntfs.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [fs/xfs/xfs.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [fs/btrfs/btrfs.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/acpi/acpi_pad.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/gpu/drm/display/drm_display_helper.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/gpu/drm/drm.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/gpu/drm/ttm/ttm.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/gpu/drm/i915/i915.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/misc/mei/mei.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/usb/core/usbcore.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/usb/class/cdc-acm.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/usb/class/usblp.ko] has no CRC!
WARNING: modpost: "const_pcpu_hot" [drivers/usb/storage/usb-storage.ko] has no CRC!

And the usual fix for those things:

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index b1a98fa38828..7e6440bae63d 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -13,6 +13,7 @@
 #include <asm/preempt.h>
 #include <asm/asm.h>
 #include <asm/gsseg.h>
+#include <asm/current.h>
 
 #ifndef CONFIG_X86_CMPXCHG64
 extern void cmpxchg8b_emu(void);

does NOT fix it.

-- 
Regards/Gruss,
    Boris.

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