linux-kernel - Re: [PATCH v4 09/12] x86/mtrr: construct a memory map with cache modes

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Message-ID: <73226c11-4443-1e52-4566-5799d21e4ccb@suse.com>
Date:   Fri, 31 Mar 2023 15:35:07 +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 v4 09/12] x86/mtrr: construct a memory map with cache
 modes

On 31.03.23 14:57, Borislav Petkov wrote:
> On Mon, Mar 06, 2023 at 05:34:22PM +0100, Juergen Gross wrote:
>> +/* Build the cache_map containing the cache modes per memory range. */
>> +void mtrr_build_map(void)
>> +{
>> +	unsigned int i;
>> +	u64 start, end, size;
>> +	u8 type;
>> +
>> +	if (!mtrr_state.enabled)
> 	     ^^^^^^^^^^^^^^^^^^^
> 
>> +		return;
>> +
>> +	/* Add fixed MTRRs, optimize for adjacent entries with same type. */
>> +	if (mtrr_state.enabled & MTRR_STATE_MTRR_FIXED_ENABLED) {
> 	    ^^^^^^^^^^^^^^^^^^
> 
> First check can go.

Hmm, this makes it much harder to see that the code really does nothing
if enabled isn't set.

> 
>> +		start = 0;
>> +		end = size = 0x10000;
>> +		type = mtrr_state.fixed_ranges[0];
>> +
>> +		for (i = 1; i < MTRR_NUM_FIXED_RANGES; i++) {
> 
> Loops starts at 1. Comment explaining why pls.

Okay.

> 
>> +			if (i == 8 || i == 24)
> 
> Magic numbers.

I'll add more comments.

> 
> Ok, I'll stop here.
> 
> Please send a new version with the review comments incorporated. I need
> to look more at that map thing more.

Will do.


Thanks,

Juergen


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