linux-kernel - Re: [PATCH v2 2/6] x86, mm, pat: Change reserve

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Date:	Fri, 12 Sep 2014 15:41:58 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	hpa@...or.com, tglx@...utronix.de, mingo@...hat.com,
	akpm@...ux-foundation.org, arnd@...db.de, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, jgross@...e.com,
	stefan.bader@...onical.com, luto@...capital.net, hmh@....eng.br,
	yigal@...xistor.com
Subject: Re: [PATCH v2 2/6] x86, mm, pat: Change reserve_memtype() to handle
 WT

On Wed, Sep 10, 2014 at 10:51:46AM -0600, Toshi Kani wrote:
> This patch changes reserve_memtype() to handle the WT cache mode.
> When PAT is not enabled, it continues to set UC- to *new_type for
> any non-WB request.
> 
> When a target range is RAM, reserve_ram_pages_type() fails for WT
> for now.  This function may not reserve a RAM range for WT since
> reserve_ram_pages_type() uses the page flags limited to three memory
> types, WB, WC and UC.
> 
> Signed-off-by: Toshi Kani <toshi.kani@...com>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  arch/x86/include/asm/cacheflush.h |    4 ++++
>  arch/x86/mm/pat.c                 |   16 +++++++++++++---
>  2 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/cacheflush.h b/arch/x86/include/asm/cacheflush.h
> index 157644b..c912680 100644
> --- a/arch/x86/include/asm/cacheflush.h
> +++ b/arch/x86/include/asm/cacheflush.h
> @@ -53,6 +53,10 @@ static inline void set_page_memtype(struct page *pg,
>  	case _PAGE_CACHE_MODE_WB:
>  		memtype_flags = _PGMT_WB;
>  		break;
> +	case _PAGE_CACHE_MODE_WT:
> +	case _PAGE_CACHE_MODE_WP:
> +		pr_err("set_page_memtype: unsupported cachemode %d\n", memtype);
> +		BUG();
>  	default:
>  		memtype_flags = _PGMT_DEFAULT;
>  		break;
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 598d7c7..7644967 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -268,6 +268,8 @@ static int pat_pagerange_is_ram(resource_size_t start, resource_size_t end)
>  
>  /*
>   * For RAM pages, we use page flags to mark the pages with appropriate type.
> + * The page flags are currently limited to three types, WB, WC and UC. Hence,
> + * any request to WT or WP will fail with -EINVAL.
>   * Here we do two pass:
>   * - Find the memtype of all the pages in the range, look for any conflicts
>   * - In case of no conflicts, set the new memtype for pages in the range
> @@ -279,6 +281,13 @@ static int reserve_ram_pages_type(u64 start, u64 end,
>  	struct page *page;
>  	u64 pfn;
>  
> +	if ((req_type == _PAGE_CACHE_MODE_WT) ||
> +	    (req_type == _PAGE_CACHE_MODE_WP)) {
> +		if (new_type)
> +			*new_type = _PAGE_CACHE_MODE_UC_MINUS;
> +		return -EINVAL;
> +	}
> +
>  	if (req_type == _PAGE_CACHE_MODE_UC) {
>  		/* We do not support strong UC */
>  		WARN_ON_ONCE(1);
> @@ -328,6 +337,7 @@ static int free_ram_pages_type(u64 start, u64 end)
>   * - _PAGE_CACHE_MODE_WC
>   * - _PAGE_CACHE_MODE_UC_MINUS
>   * - _PAGE_CACHE_MODE_UC
> + * - _PAGE_CACHE_MODE_WT
>   *
>   * If new_type is NULL, function will return an error if it cannot reserve the
>   * region with req_type. If new_type is non-NULL, function will return
> @@ -347,10 +357,10 @@ int reserve_memtype(u64 start, u64 end, enum page_cache_mode req_type,
>  	if (!pat_enabled) {
>  		/* This is identical to page table setting without PAT */
>  		if (new_type) {
> -			if (req_type == _PAGE_CACHE_MODE_WC)
> -				*new_type = _PAGE_CACHE_MODE_UC_MINUS;
> +			if (req_type == _PAGE_CACHE_MODE_WB)
> +				*new_type = _PAGE_CACHE_MODE_WB;
>  			else
> -				*new_type = req_type;
> +				*new_type = _PAGE_CACHE_MODE_UC_MINUS;
>  		}
>  		return 0;
>  	}
--
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