linux-kernel - Re: [PATCH v2 3/9] mm/huge_page: cleanup clear_/copy

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Date:   Fri, 8 Sep 2023 14:09:52 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Ankur Arora <ankur.a.arora@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org, mgorman@...e.de,
        peterz@...radead.org, rostedt@...dmis.org, tglx@...utronix.de,
        jon.grimm@....com, bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v2 3/9] mm/huge_page: cleanup clear_/copy_subpage()

On Wed, Aug 30, 2023 at 11:49:52AM -0700, Ankur Arora wrote:
> @@ -5945,9 +5935,7 @@ static int __clear_huge_page(
>  		/* Process subpages at the end of huge page */
>  		for (i = pages_per_huge_page - 1; i >= 2 * n; i--) {
>  			cond_resched();
> -			ret = process_subpage(addr + i * PAGE_SIZE, i, arg);
> -			if (ret)
> -				return ret;
> +			clear_user_highpage(page + i, addr + i * PAGE_SIZE);

It's possible for a 1GB page to cross a memmap discontiguity.  This
needs to be:

			clear_user_highpage(nth_page(page, i),
					addr + i * PAGE_SIZE);

(similarly in other places)