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Date: Fri, 5 Apr 2024 04:29:56 +0100
From: Matthew Wilcox <willy@infradead.org>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-s390@vger.kernel.org, kvm@vger.kernel.org,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
	Thomas Huth <thuth@redhat.com>
Subject: Re: [PATCH v1 2/5] s390/uv: convert gmap_make_secure() to work on
 folios
Message-ID: <Zg9wNKTu4JxGXrHs@casper.infradead.org>
References: <20240404163642.1125529-1-david@redhat.com>
 <20240404163642.1125529-3-david@redhat.com>
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In-Reply-To: <20240404163642.1125529-3-david@redhat.com>

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?