Re: [PATCH] [v2] x86: coco: replace static const cc_mask with a function

[Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>]

On 3/10/25 6:10 AM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> When extra warnings are enabled, the cc_mask definition in asm/coco.h
> causes a build failure with gcc:
>
> arch/x86/include/asm/coco.h:28:18: error: 'cc_mask' defined but not used [-Werror=unused-const-variable=]
>     28 | static const u64 cc_mask = 0;
>
> Add a cc_get_mask() function mirroring cc_set_mask() for the one
> user of the variable outside of the coco implementation.
>
> Fixes: a0a8d15a798b ("x86/tdx: Preserve shared bit on mprotect()")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> --

Reviewed-by: Kuppuswamy Sathyanarayanan 
<sathyanarayanan.kuppuswamy@linux.intel.com>

> v2: use an inline helper instead of a __maybe_unused annotaiton.
> ---
>   arch/x86/include/asm/coco.h          | 10 +++++++++-
>   arch/x86/include/asm/pgtable_types.h |  2 +-
>   2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/coco.h b/arch/x86/include/asm/coco.h
> index aa6c8f8ca958..e7225452963f 100644
> --- a/arch/x86/include/asm/coco.h
> +++ b/arch/x86/include/asm/coco.h
> @@ -15,6 +15,11 @@ enum cc_vendor {
>   extern enum cc_vendor cc_vendor;
>   extern u64 cc_mask;
>   
> +static inline u64 cc_get_mask(void)
> +{
> +	return cc_mask;
> +}
> +
>   static inline void cc_set_mask(u64 mask)
>   {
>   	RIP_REL_REF(cc_mask) = mask;
> @@ -25,7 +30,10 @@ u64 cc_mkdec(u64 val);
>   void cc_random_init(void);
>   #else
>   #define cc_vendor (CC_VENDOR_NONE)
> -static const u64 cc_mask = 0;
> +static inline u64 cc_get_mask(void)
> +{
> +	return 0;
> +}
>   
>   static inline u64 cc_mkenc(u64 val)
>   {
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index c90e9c51edb7..74d461cc8e20 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -179,7 +179,7 @@ enum page_cache_mode {
>   };
>   #endif
>   
> -#define _PAGE_CC		(_AT(pteval_t, cc_mask))
> +#define _PAGE_CC		(_AT(pteval_t, cc_get_mask()))
>   #define _PAGE_ENC		(_AT(pteval_t, sme_me_mask))
>   
>   #define _PAGE_CACHE_MASK	(_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer