Re: [Xen-devel] [PATCH V4 1/3] x86: Make page cache mode a real type

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Mon, 27 Oct 2014, Juergen Gross wrote:
> At the moment there are a lot of places that handle setting or getting
> the page cache mode by treating the pgprot bits equal to the cache mode.
> This is only true because there are a lot of assumptions about the setup
> of the PAT MSR. Otherwise the cache type needs to get translated into
> pgprot bits and vice versa.
> 
> This patch tries to prepare for that by introducing a separate type
> for the cache mode and adding functions to translate between those and
> pgprot values.
> 
> To avoid too much performance penalty the translation between cache mode
> and pgprot values is done via tables which contain the relevant
> information.  Write-back cache mode is hard-wired to be 0, all other
> modes are configurable via those tables. For large pages there are
> translation functions as the PAT bit is located at different positions
> in the ptes of 4k and large pages.

I'm fine with the approach itself. Though I wish you had split this
patch in several sanely to review pieces.

  - Introduce enums, helper functions etc. which basically reflect
    the state of today

  - Change the usage sites to use the enums and helpers

  - Convert the enum/helper implementation to the new scheme

  - Split out the printk change

  ...

Thanks,

        tglx

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