Re: [PATCH] x86/mm/pat: Initialize __cachemode2pte_tbl[] and __pte2cachemode_tbl[] in a bit more readable fashion

Juergen Gross
2015-03-05T08:42:24Z

On 03/05/2015 09:21 AM, Ingo Molnar wrote:
>
> ( So this patch is not directly related to gbpages, but while reading
> arch/x86/mm/init.c I could not resist ... )
>
> =======================>
>
> The initialization of these two arrays is a bit difficult to follow:
> restructure it optically so that a 2D structure shows which bit in
> the PTE is set and which not.
>
> Also improve on comments a bit.
>
> No code or data changed:
>
> # arch/x86/mm/init.o:
>
> text data bss dec hex filename
> 4585 424 29776 34785 87e1 init.o.before
> 4585 424 29776 34785 87e1 init.o.after
>
> md5:
> a82e11ff58bcfd0af3a94662a701f65d init.o.before.asm
> a82e11ff58bcfd0af3a94662a701f65d init.o.after.asm
>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Jan Beulich <JBeulich@suse.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Luis R. Rodriguez <mcgrof@suse.com>
> Cc: Toshi Kani <toshi.kani@hp.com>
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Ingo Molnar <mingo@kernel.org>

Reviewed-by: Juergen Gross <jgross@suse.com>

> ---
> arch/x86/mm/init.c | 40 ++++++++++++++++++++++------------------
> 1 file changed, 22 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 6dc85d51cd98..4469563f8c3b 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -29,29 +29,33 @@
>
> /*
> * Tables translating between page_cache_type_t and pte encoding.
> - * Minimal supported modes are defined statically, modified if more supported
> - * cache modes are available.
> - * Index into __cachemode2pte_tbl is the cachemode.
> - * Index into __pte2cachemode_tbl are the caching attribute bits of the pte
> - * (_PAGE_PWT, _PAGE_PCD, _PAGE_PAT) at index bit positions 0, 1, 2.
> + *
> + * Minimal supported modes are defined statically, they are modified
> + * during bootup if more supported cache modes are available.
> + *
> + * Index into __cachemode2pte_tbl[] is the cachemode.
> + *
> + * Index into __pte2cachemode_tbl[] are the caching attribute bits of the pte
> + * (_PAGE_PWT, _PAGE_PCD, _PAGE_PAT) at index bit positions 0, 1, 2.
> */
> uint16_t __cachemode2pte_tbl[_PAGE_CACHE_MODE_NUM] = {
> - [_PAGE_CACHE_MODE_WB] = 0,
> - [_PAGE_CACHE_MODE_WC] = _PAGE_PWT,
> - [_PAGE_CACHE_MODE_UC_MINUS] = _PAGE_PCD,
> - [_PAGE_CACHE_MODE_UC] = _PAGE_PCD | _PAGE_PWT,
> - [_PAGE_CACHE_MODE_WT] = _PAGE_PCD,
> - [_PAGE_CACHE_MODE_WP] = _PAGE_PCD,
> + [_PAGE_CACHE_MODE_WB ] = 0 | 0 ,
> + [_PAGE_CACHE_MODE_WC ] = _PAGE_PWT | 0 ,
> + [_PAGE_CACHE_MODE_UC_MINUS] = 0 | _PAGE_PCD,
> + [_PAGE_CACHE_MODE_UC ] = _PAGE_PWT | _PAGE_PCD,
> + [_PAGE_CACHE_MODE_WT ] = 0 | _PAGE_PCD,
> + [_PAGE_CACHE_MODE_WP ] = 0 | _PAGE_PCD,
> };
> EXPORT_SYMBOL(__cachemode2pte_tbl);
> +
> uint8_t __pte2cachemode_tbl[8] = {
> - [__pte2cm_idx(0)] = _PAGE_CACHE_MODE_WB,
> - [__pte2cm_idx(_PAGE_PWT)] = _PAGE_CACHE_MODE_WC,
> - [__pte2cm_idx(_PAGE_PCD)] = _PAGE_CACHE_MODE_UC_MINUS,
> - [__pte2cm_idx(_PAGE_PWT | _PAGE_PCD)] = _PAGE_CACHE_MODE_UC,
> - [__pte2cm_idx(_PAGE_PAT)] = _PAGE_CACHE_MODE_WB,
> - [__pte2cm_idx(_PAGE_PWT | _PAGE_PAT)] = _PAGE_CACHE_MODE_WC,
> - [__pte2cm_idx(_PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC_MINUS,
> + [__pte2cm_idx( 0 | 0 | 0 )] = _PAGE_CACHE_MODE_WB,
> + [__pte2cm_idx(_PAGE_PWT | 0 | 0 )] = _PAGE_CACHE_MODE_WC,
> + [__pte2cm_idx( 0 | _PAGE_PCD | 0 )] = _PAGE_CACHE_MODE_UC_MINUS,
> + [__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | 0 )] = _PAGE_CACHE_MODE_UC,
> + [__pte2cm_idx( 0 | 0 | _PAGE_PAT)] = _PAGE_CACHE_MODE_WB,
> + [__pte2cm_idx(_PAGE_PWT | 0 | _PAGE_PAT)] = _PAGE_CACHE_MODE_WC,
> + [__pte2cm_idx(0 | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC_MINUS,
> [__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC,
> };
> EXPORT_SYMBOL(__pte2cachemode_tbl);
> --
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