linux-kernel - Re: [PATCH v4 6/7] mtrr, x86: Clean up mtrr_type

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Message-ID: <20150507075210.GA6859@pd.tnic>
Date:	Thu, 7 May 2015 09:52:10 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Toshi Kani <toshi.kani@...com>
Cc:	akpm@...ux-foundation.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, linux-mm@...ck.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, dave.hansen@...el.com,
	Elliott@...com, pebolle@...cali.nl
Subject: Re: [PATCH v4 6/7] mtrr, x86: Clean up mtrr_type_lookup()

On Wed, May 06, 2015 at 05:42:10PM -0600, Toshi Kani wrote:
> Well, creating mtrr_type_lookup_fixed() is one of the comments I had in
> the previous code review.  Anyway, let me make sure if I understand your
> comment correctly.  Do the following changes look right to you?
> 
> 1) Change the caller responsible for the condition checks.
> 
>         if ((start < 0x100000) &&
>             (mtrr_state.have_fixed) &&
>             (mtrr_state.enabled & MTRR_STATE_MTRR_FIXED_ENABLED))
>                 return mtrr_type_lookup_fixed(start, end);
> 
> 2) Delete the checks with mtrr_state in mtrr_type_lookup_fixed() as they
> are done by the caller.  Keep the check with '(start >= 0x100000)' to
> assure that the code handles the range [0xC0000 - 0xFFFFF] correctly.

That is a good defensive measure.

> static u8 mtrr_type_lookup_fixed(u64 start, u64 end)
> {
>         int idx;
> 
>         if (start >= 0x100000)
>                  return MTRR_TYPE_INVALID;
>  
> -       if (!(mtrr_state.have_fixed) ||
> -           !(mtrr_state.enabled & MTRR_STATE_MTRR_FIXED_ENABLED))
> -               return MTRR_TYPE_INVALID;

Yeah, that's what I mean.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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