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Date: Wed, 29 Oct 2014 11:56:48 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Juergen Gross <jgross@...e.com>
Cc: hpa@...or.com, x86@...nel.org, tglx@...utronix.de,
mingo@...hat.com, stefan.bader@...onical.com,
linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
konrad.wilk@...cle.com, ville.syrjala@...ux.intel.com,
david.vrabel@...rix.com, jbeulich@...e.com, toshi.kani@...com
Subject: Re: [PATCH V4 2/3] x86: Enable PAT to use cache mode translation
tables
* Juergen Gross <jgross@...e.com> wrote:
> Update the translation tables from cache mode to pgprot values
> according to the PAT settings. This enables changing the cache
> attributes of a PAT index in just one place without having to change
> at the users side.
>
> With this change it is possible to use the same kernel with different
> PAT configurations, e.g. supporting Xen.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> Reviewed-by: Toshi Kani <toshi.kani@...com>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
> arch/x86/include/asm/pat.h | 1 +
> arch/x86/include/asm/pgtable_types.h | 4 +++
> arch/x86/mm/init.c | 8 ++++++
> arch/x86/mm/mm_internal.h | 2 ++
> arch/x86/mm/pat.c | 55 ++++++++++++++++++++++++++++++++++--
> 5 files changed, 68 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
> index 150407a..91bc4ba 100644
> --- a/arch/x86/include/asm/pat.h
> +++ b/arch/x86/include/asm/pat.h
> @@ -11,6 +11,7 @@ static const int pat_enabled;
> #endif
>
> extern void pat_init(void);
> +void pat_init_cache_modes(void);
>
> extern int reserve_memtype(u64 start, u64 end,
> enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 3a6cbb9..31c66c6 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -351,6 +351,10 @@ extern uint8_t __pte2cachemode_tbl[8];
> ((((cb) >> (_PAGE_BIT_PAT - 2)) & 4) | \
> (((cb) >> (_PAGE_BIT_PCD - 1)) & 2) | \
> (((cb) >> _PAGE_BIT_PWT) & 1))
> +#define __cm_idx2pte(i) \
> + ((((i) & 4) << (_PAGE_BIT_PAT - 2)) | \
> + (((i) & 2) << (_PAGE_BIT_PCD - 1)) | \
> + (((i) & 1) << _PAGE_BIT_PWT))
>
> static inline unsigned long cachemode2protval(enum page_cache_mode pcm)
> {
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index a9776ba..82b41d5 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -716,3 +716,11 @@ void __init zone_sizes_init(void)
> free_area_init_nodes(max_zone_pfns);
> }
>
> +void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache)
> +{
> + /* entry 0 MUST be WB (hardwired to speed up translations) */
> + BUG_ON(!entry && cache != _PAGE_CACHE_MODE_WB);
> +
> + __cachemode2pte_tbl[cache] = __cm_idx2pte(entry);
> + __pte2cachemode_tbl[entry] = cache;
> +}
> diff --git a/arch/x86/mm/mm_internal.h b/arch/x86/mm/mm_internal.h
> index 6b563a1..62474ba 100644
> --- a/arch/x86/mm/mm_internal.h
> +++ b/arch/x86/mm/mm_internal.h
> @@ -16,4 +16,6 @@ void zone_sizes_init(void);
>
> extern int after_bootmem;
>
> +void update_cache_mode_entry(unsigned entry, enum page_cache_mode cache);
> +
> #endif /* __X86_MM_INTERNAL_H */
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index ef75f3f..ff31851 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -31,6 +31,7 @@
> #include <asm/io.h>
>
> #include "pat_internal.h"
> +#include "mm_internal.h"
>
> #ifdef CONFIG_X86_PAT
> int __read_mostly pat_enabled = 1;
> @@ -75,6 +76,57 @@ enum {
> PAT_UC_MINUS = 7, /* UC, but can be overriden by MTRR */
> };
>
> +/*
> + * Update the cache mode to pgprot translation tables according to PAT
> + * configuration.
> + * Using lower indices is preferred, so we start with highest index.
> + */
> +void pat_init_cache_modes(void)
> +{
> + int i;
> + enum page_cache_mode cache;
> + char pat_msg[33];
> + char *cache_mode;
> + u64 pat;
> +
> + rdmsrl(MSR_IA32_CR_PAT, pat);
> + pat_msg[32] = 0;
> + for (i = 7; i >= 0; i--) {
> + switch ((pat >> (i * 8)) & 7) {
> + case PAT_UC:
> + cache = _PAGE_CACHE_MODE_UC;
> + cache_mode = "UC ";
> + break;
> + case PAT_WC:
> + cache = _PAGE_CACHE_MODE_WC;
> + cache_mode = "WC ";
> + break;
> + case PAT_WT:
> + cache = _PAGE_CACHE_MODE_WT;
> + cache_mode = "WT ";
> + break;
> + case PAT_WP:
> + cache = _PAGE_CACHE_MODE_WP;
> + cache_mode = "WP ";
> + break;
> + case PAT_WB:
> + cache = _PAGE_CACHE_MODE_WB;
> + cache_mode = "WB ";
> + break;
> + case PAT_UC_MINUS:
> + cache = _PAGE_CACHE_MODE_UC_MINUS;
> + cache_mode = "UC- ";
> + break;
> + default:
> + cache = _PAGE_CACHE_MODE_WB;
> + cache_mode = "WB ";
Please put the iterator into a helper function to make it all
easier to read.
Within that helper function I'd also suggest organizing the
initialization the following way:
case PAT_UC: cache = _PAGE_CACHE_MODE_UC; cache_mode = "UC "; break;
case PAT_WC: cache = _PAGE_CACHE_MODE_WC; cache_mode = "WC "; break;
case PAT_WT: cache = _PAGE_CACHE_MODE_WT; cache_mode = "WT "; break;
...
case PAT_UC_MINUS: cache = _PAGE_CACHE_MODE_UC_MINUS; cache_mode = "UC- "; break;
default: cache = _PAGE_CACHE_MODE_WB; cache_mode = "WB "; break;
Note how it's all tabular, vertically aligned and thus easier to
cross check and review this way.
Thanks,
Ingo
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