From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:19654 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728371AbgDGLKw (ORCPT ); Tue, 7 Apr 2020 07:10:52 -0400 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 037B2pus094512 for ; Tue, 7 Apr 2020 07:10:51 -0400 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 3082hgm9wt-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 07 Apr 2020 07:10:51 -0400 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 7 Apr 2020 12:10:22 +0100 Date: Tue, 7 Apr 2020 13:05:22 +0200 From: Claudio Imbrenda Subject: Re: [PATCH v2 3/5] KVM: s390: vsie: Fix possible race when shadowing region 3 tables In-Reply-To: <20200403153050.20569-4-david@redhat.com> References: <20200403153050.20569-1-david@redhat.com> <20200403153050.20569-4-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20200407130522.189a9a3f@p-imbrenda> Sender: linux-s390-owner@vger.kernel.org List-ID: To: David Hildenbrand Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Vasily Gorbik , Heiko Carstens , Cornelia Huck , Janosch Frank , Christian Borntraeger On Fri, 3 Apr 2020 17:30:48 +0200 David Hildenbrand wrote: > We have to properly retry again by returning -EINVAL immediately in > case somebody else instantiated the table concurrently. We missed to > add the goto in this function only. The code now matches the other, > similar shadowing functions. > > We are overwriting an existing region 2 table entry. All allocated > pages are added to the crst_list to be freed later, so they are not > lost forever. However, when unshadowing the region 2 table, we > wouldn't trigger unshadowing of the original shadowed region 3 table > that we replaced. It would get unshadowed when the original region 3 > table is modified. As it's not connected to the page table hierarchy > anymore, it's not going to get used anymore. However, for a limited > time, this page table will stick around, so it's in some sense a > temporary memory leak. > > Identified by manual code inspection. I don't think this classifies as > stable material. > > Fixes: 998f637cc4b9 ("s390/mm: avoid races on region/segment/page > table shadowing") Signed-off-by: David Hildenbrand > --- > arch/s390/mm/gmap.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c > index b93dd54b234a..24ef30fb0833 100644 > --- a/arch/s390/mm/gmap.c > +++ b/arch/s390/mm/gmap.c > @@ -1844,6 +1844,7 @@ int gmap_shadow_r3t(struct gmap *sg, unsigned > long saddr, unsigned long r3t, goto out_free; > } else if (*table & _REGION_ENTRY_ORIGIN) { > rc = -EAGAIN; /* Race with shadow */ > + goto out_free; > } > crst_table_init(s_r3t, _REGION3_ENTRY_EMPTY); > /* mark as invalid as long as the parent table is not > protected */ Reviewed-by: Claudio Imbrenda