linux-kernel - Re: [PATCH v1 2/5] s390/uv: convert gmap_make

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Date: Fri, 5 Apr 2024 04:29:56 +0100
From: Matthew Wilcox <willy@...radead.org>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-s390@...r.kernel.org, kvm@...r.kernel.org,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Thomas Huth <thuth@...hat.com>
Subject: Re: [PATCH v1 2/5] s390/uv: convert gmap_make_secure() to work on
 folios

On Thu, Apr 04, 2024 at 06:36:39PM +0200, David Hildenbrand wrote:
> +		/* We might get PTE-mapped large folios; split them first. */
> +		if (folio_test_large(folio)) {
> +			rc = -E2BIG;

We agree to this point.  I just turned this into -EINVAL.

>  
> +	if (rc == -E2BIG) {
> +		/*
> +		 * Splitting might fail with -EBUSY due to unexpected folio
> +		 * references, just like make_folio_secure(). So handle it
> +		 * ahead of time without the PTL being held.
> +		 */
> +		folio_lock(folio);
> +		rc = split_folio(folio);
> +		folio_unlock(folio);
> +		folio_put(folio);
> +	}

Ummm ... if split_folio() succeeds, aren't we going to return 0 from
this function, which will be interpreted as make_folio_secure() having
succeeded?