Re: [Xen-devel] [PATCH RFC 1/3] x86: Make page cache mode a real type

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.08.14 at 11:30, <JGross@xxxxxxxx> wrote:
> On 08/20/2014 09:26 PM, Toshi Kani wrote:
>> On Tue, 2014-08-19 at 15:25 +0200, jgross@xxxxxxxx wrote:
>>> --- a/arch/x86/mm/init.c
>>> +++ b/arch/x86/mm/init.c
>>> @@ -27,6 +27,35 @@
>>>
>>>   #include "mm_internal.h"
>>>
>>> +/*
>>> + * 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.
>>> + */
>>> +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_PWT,
>>> +   [_PAGE_CACHE_MODE_WP]           = _PAGE_PWT,
>>> +};
>>
>> I think WT and WP should be set to _PAGE_PCD (UC_MINUS) for safe.
> 
> Oh, you are right.

Actually I suppose the original comment was about WC and WP;
defaulting WT to _PAGE_PWT seems quite correct to me.

Jan


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