linux-kernel - Re: [PATCH v4 5/7] x86, mm, pat: Refactor !pat

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Message-ID: <alpine.DEB.2.11.1411031957330.5308@nanos>
Date:	Mon, 3 Nov 2014 20:01:26 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Toshi Kani <toshi.kani@...com>
cc:	hpa@...or.com, 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, konrad.wilk@...cle.com
Subject: Re: [PATCH v4 5/7] x86, mm, pat: Refactor !pat_enabled handling

On Mon, 27 Oct 2014, Toshi Kani wrote:
> diff --git a/arch/x86/mm/iomap_32.c b/arch/x86/mm/iomap_32.c
> index ee58a0b..96aa8bf 100644
> --- a/arch/x86/mm/iomap_32.c
> +++ b/arch/x86/mm/iomap_32.c
> @@ -70,29 +70,23 @@ void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>  	return (void *)vaddr;
>  }
>  
> -/*
> - * Map 'pfn' using protections 'prot'
> - */
> -#define __PAGE_KERNEL_WC	(__PAGE_KERNEL | \
> -				 cachemode2protval(_PAGE_CACHE_MODE_WC))
> -
>  void __iomem *
>  iomap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
>  {
>  	/*
> -	 * For non-PAT systems, promote PAGE_KERNEL_WC to PAGE_KERNEL_UC_MINUS.
> -	 * PAGE_KERNEL_WC maps to PWT, which translates to uncached if the
> -	 * MTRR is UC or WC.  UC_MINUS gets the real intention, of the
> -	 * user, which is "WC if the MTRR is WC, UC if you can't do that."
> +	 * For non-PAT systems, translate non-WB request to UC- just in
> +	 * case the caller set the PWT bit to prot directly without using
> +	 * pgprot_writecombine(). UC- translates to uncached if the MTRR
> +	 * is UC or WC. UC- gets the real intention, of the user, which is
> +	 * "WC if the MTRR is WC, UC if you can't do that."
>  	 */
> -	if (!pat_enabled && pgprot_val(prot) == __PAGE_KERNEL_WC)
> +	if (!pat_enabled && pgprot2cachemode(prot) != _PAGE_CACHE_MODE_WB)
>  		prot = __pgprot(__PAGE_KERNEL |
>  				cachemode2protval(_PAGE_CACHE_MODE_UC_MINUS));
>  
>  	return (void __force __iomem *) kmap_atomic_prot_pfn(pfn, prot);
>  }
>  EXPORT_SYMBOL_GPL(iomap_atomic_prot_pfn);
> -#undef __PAGE_KERNEL_WC

Rejects. Please update against Juergens latest.
  
Thanks,

	tglx
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