linux-kernel - Re: [PATCH v5 03/15] x86/mtrr: replace some constants with defines

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Date:   Tue, 11 Apr 2023 15:32:25 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v5 03/15] x86/mtrr: replace some constants with defines

On 05.04.23 22:26, Borislav Petkov wrote:
> On Wed, Apr 05, 2023 at 09:55:59AM +0200, Juergen Gross wrote:
>> On 03.04.23 18:03, Borislav Petkov wrote:
>>> On Sat, Apr 01, 2023 at 08:36:40AM +0200, Juergen Gross wrote:
>>>> @@ -643,10 +646,12 @@ static bool set_mtrr_var_ranges(unsigned int index, struct mtrr_var_range *vr)
>>>>    	unsigned int lo, hi;
>>>>    	bool changed = false;
>>>> +#define BASE_MASK	(MTRR_BASE_TYPE_MASK | (size_and_mask << PAGE_SHIFT))
>>>> +#define MASK_MASK	(MTRR_MASK_VALID | (size_and_mask << PAGE_SHIFT))
>>>
>>> No, "MASK_MASK" is too much. :-)
>>
>> Any better suggestion for the name? :-)
> 
> Looking at this again, what this is actually doing is masking out the
> reserved bits. But in an unnecessarily complicated way.
> 
> What it should do, instead, is do that explicitly:
> 
> 	/* Zap the reserved bits and compare only the valid fields: */
> 	if (((vr->base_lo & ~RESV_LOW) != (lo & ~RESV_LOW)) ||
> 	    ((vr->base_hi & ~RESV_HI) != (hi & ~RESV_HI)))
> 
> where
> 
> #define RESV_LOW	GENMASK_ULL(8, 11)
> #define RESV_HI		GENMASK(phys_addr - 1, 63)
> 
> and then we can get rid of that size_or_mask and size_and_mask
> stupidity.
> 
> I think that would simplify this variable ranges handling code a lot
> more and make it pretty straightforward...

Yeah, probably a good idea.


Juergen

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