linux-kernel - Re: [PATCH 2/2] x86/mm/pat: Change free

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Date:	Sun, 20 Dec 2015 10:27:51 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Toshi Kani <toshi.kani@....com>
cc:	mingo@...hat.com, hpa@...or.com, bp@...en8.de, stsp@...t.ru,
	x86@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 2/2] x86/mm/pat: Change free_memtype() to free shrinking
 range

Toshi,

On Wed, 9 Dec 2015, Toshi Kani wrote:
> diff --git a/arch/x86/mm/pat_rbtree.c b/arch/x86/mm/pat_rbtree.c
> index 6393108..d6faef8 100644
> --- a/arch/x86/mm/pat_rbtree.c
> +++ b/arch/x86/mm/pat_rbtree.c
> @@ -107,7 +112,12 @@ static struct memtype *memtype_rb_exact_match(struct rb_root *root,
>  	while (match != NULL && match->start < end) {
>  		struct rb_node *node;
>  
> -		if (match->start == start && match->end == end)
> +		if ((match_type == MEMTYPE_EXACT_MATCH) &&
> +		    (match->start == start) && (match->end == end))
> +			return match;
> +
> +		if ((match_type == MEMTYPE_SHRINK_MATCH) &&
> +		    (match->start < start) && (match->end == end))

Confused. If we shrink a mapping then I'd expect that the start of the
mapping stays the same and the end changes. I certainly miss something
here, but if the above is correct, then it definitely needs a big fat
comment explaining it.

Thanks,

	tglx


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