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Wed, 11 Mar 2026 14:17:23 +0000 (GMT) Message-ID: <799ed972-6527-4cc3-8c37-30c07d30adaa@linux.ibm.com> Date: Wed, 11 Mar 2026 15:17:22 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] s390/mm: add missing secure storage access fixups for donated memory To: Heiko Carstens Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, imbrenda@linux.ibm.com, borntraeger@linux.ibm.com, linux-kernel@vger.kernel.org References: <20260310150408.160722-1-frankja@linux.ibm.com> <20260311070053.9469A4e-hca@linux.ibm.com> Content-Language: en-US From: Janosch Frank Autocrypt: addr=frankja@linux.ibm.com; keydata= xsFNBFubpD4BEADX0uhkRhkj2AVn7kI4IuPY3A8xKat0ihuPDXbynUC77mNox7yvK3X5QBO6 qLqYr+qrG3buymJJRD9xkp4mqgasHdB5WR9MhXWKH08EvtvAMkEJLnqxgbqf8td3pCQ2cEpv 15mH49iKSmlTcJ+PvJpGZcq/jE42u9/0YFHhozm8GfQdb9SOI/wBSsOqcXcLTUeAvbdqSBZe zuMRBivJQQI1esD9HuADmxdE7c4AeMlap9MvxvUtWk4ZJ/1Z3swMVCGzZb2Xg/9jZpLsyQzb lDbbTlEeyBACeED7DYLZI3d0SFKeJZ1SUyMmSOcr9zeSh4S4h4w8xgDDGmeDVygBQZa1HaoL Esb8Y4avOYIgYDhgkCh0nol7XQ5i/yKLtnNThubAcxNyryw1xSstnKlxPRoxtqTsxMAiSekk 0m3WJwvwd1s878HrQNK0orWd8BzzlSswzjNfQYLF466JOjHPWFOok9pzRs+ucrs6MUwDJj0S cITWU9Rxb04XyigY4XmZ8dywaxwi2ZVTEg+MD+sPmRrTw+5F+sU83cUstuymF3w1GmyofgsU Z+/ldjToHnq21MNa1wx0lCEipCCyE/8K9B9bg9pUwy5lfx7yORP3JuAUfCYb8DVSHWBPHKNj HTOLb2g2UT65AjZEQE95U2AY9iYm5usMqaWD39pAHfhC09/7NQARAQABzSVKYW5vc2NoIEZy YW5rIDxmcmFua2phQGxpbnV4LmlibS5jb20+wsF3BBMBCAAhBQJbm6Q+AhsjBQsJCAcCBhUI CQoLAgQWAgMBAh4BAheAAAoJEONU5rjiOLn4p9gQALjkdj5euJVI2nNT3/IAxAhQSmRhPEt0 AmnCYnuTcHRWPujNr5kqgtyER9+EMQ0ZkX44JU2q7OWxTdSNSAN/5Z7qmOR9JySvDOf4d3mS bMB5zxL9d8SbnSs1uW96H9ZBTlTQnmLfsiM9TetAjSrR8nUmjGhe2YUhJLR1v1LguME+YseT eXnLzIzqqpu311/eYiiIGcmaOjPCE+vFjcXL5oLnGUE73qSYiujwhfPCCUK0850o1fUAYq5p CNBCoKT4OddZR+0itKc/cT6NwEDwdokeg0+rAhxb4Rv5oFO70lziBplEjOxu3dqgIKbHbjza EXTb+mr7VI9O4tTdqrwJo2q9zLqqOfDBi7NDvZFLzaCewhbdEpDYVu6/WxprAY94hY3F4trT rQMHJKQENtF6ZTQc9fcT5I3gAmP+OEvDE5hcTALpWm6Z6SzxO7gEYCnF+qGXqp8sJVrweMub UscyLqHoqdZC2UG4LQ1OJ97nzDpIRe0g6oJ9ZIYHKmfw5jjwH6rASTld5MFWajWdNsqK15k/ RZnHAGICKVIBOBsq26m4EsBlfCdt3b/6emuBjUXR1pyjHMz2awWzCq6/6OWs5eANZ0sdosNq dq2v0ULYTazJz2rlCXV89qRa7ukkNwdBSZNEwsD4eEMicj1LSrqWDZMAALw50L4jxaMD7lPL jJbazsFNBFubpD4BEADAcUTRqXF/aY53OSH7IwIK9lFKxIm0IoFkOEh7LMfp7FGzaP7ANrZd cIzhZi38xyOkcaFY+npGEWvko7rlIAn0JpBO4x3hfhmhBD/WSY8LQIFQNNjEm3vzrMo7b9Jb JAqQxfbURY3Dql3GUzeWTG9uaJ00u+EEPlY8zcVShDltIl5PLih20e8xgTnNzx5c110lQSu0 iZv2lAE6DM+2bJQTsMSYiwKlwTuv9LI9Chnoo6+tsN55NqyMxYqJgElk3VzlTXSr3+rtSCwf tq2cinETbzxc1XuhIX6pu/aCGnNfuEkM34b7G1D6CPzDMqokNFbyoO6DQ1+fW6c5gctXg/lZ 602iEl4C4rgcr3+EpfoPUWzKeM8JXv5Kpq4YDxhvbitr8Dm8gr38+UKFZKlWLlwhQ56r/zAU v6LIsm11GmFs2/cmgD1bqBTNHHcTWwWtRTLgmnqJbVisMJuYJt4KNPqphTWsPY8SEtbufIlY HXOJ2lqUzOReTrie2u0qcSvGAbSfec9apTFl2Xko/ddqPcZMpKhBiXmY8tJzSPk3+G4tqur4 6TYAm5ouitJsgAR61Cu7s+PNuq/pTLDhK+6/Njmc94NGBcRA4qTuysEGE79vYWP2oIAU4Fv6 gqaWHZ4MEI2XTqH8wiwzPdCQPYsSE0fXWiYu7ObeErT6iLSTZGx4rQARAQABwsFfBBgBCAAJ BQJbm6Q+AhsMAAoJEONU5rjiOLn4DDEP/RuyckW65SZcPG4cMfNgWxZF8rVjeVl/9PBfy01K 8R0hajU40bWtXSMiby7j0/dMjz99jN6L+AJHJvrLz4qYRzn2Ys843W+RfXj62Zde4YNBE5SL jJweRCbMWKaJLj6499fctxTyeb9+AMLQS4yRSwHuAZLmAb5AyCW1gBcTWZb8ON5BmWnRqeGm IgC1EvCnHy++aBnHTn0m+zV89BhTLTUal35tcjUFwluBY39R2ux/HNlBO1GY3Z+WYXhBvq7q katThLjaQSmnOrMhzqYmdShP1leFTVbzXUUIYv/GbynO/YrL2gaQpaP1bEUEi8lUAfXJbEWG dnHFkciryi092E8/9j89DJg4mmZqOau7TtUxjRMlBcIliXkzSLUk+QvD4LK1kWievJse4mte FBdkWHfP4BH/+8DxapRcG1UAheSnSRQ5LiO50annOB7oXF+vgKIaie2TBfZxQNGAs3RQ+bga DchCqFm5adiSP5+OT4NjkKUeGpBe/aRyQSle/RropTgCi85pje/juYEn2P9UAgkfBJrOHvQ9 Z+2Sva8FRd61NJLkCJ4LFumRn9wQlX2icFbi8UDV3do0hXJRRYTWCxrHscMhkrFWLhYiPF4i phX7UNdOWBQ90qpHyAxHmDazdo27gEjfvsgYMdveKknEOTEb5phwxWgg7BcIDoJf9UMC In-Reply-To: <20260311070053.9469A4e-hca@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzExMDExOSBTYWx0ZWRfX/cWxUQ37VTql FUbwtQfGYVItMEDA3B4Btpwds/LE9gqlQz2vKTALoaWlOeuU0jAA5Kx8uhcW7q88NqdFXe4G8OI hyFxJoNHM80zhIOrPG6IXCwgacc7kHl9HyT37WHXD22zMUFvd0BtydN0LYGYJnFGmR/Yb9gSKpt VijB4kcytiLCWIUi0kRQjkFQe2PkOn/yUcuXazdcRt7aS8fBAZIbOVpjWDP7W3DaLm512ZW9ukC TGBTcukfjDv4CO99OL8yM+FA5CtXo5g9bYZJTiyWGmP5iFjLyT5oea5UlUD48R88fPtHwACVvqw 3L6NSsDynJj3Lfbs6RFOKx/uk8xVEeOGroVyMZ3Ny7U/Wi7HmdxLiWkDS5iIVINeKMIsDW8Rsye 59DJQp+WoLCqyfIkj127x++Rv43WpC5Br/BJ26l2alZNBUg8nOzSEYXpxAEi9mWmsUyrSyukFe+ Et6by7aR6dEWyGMSRYA== X-Proofpoint-GUID: dC8RpSQF2Ke4dOdI4KgdlHu4AUjRWbel X-Proofpoint-ORIG-GUID: dC8RpSQF2Ke4dOdI4KgdlHu4AUjRWbel X-Authority-Analysis: v=2.4 cv=QoFTHFyd c=1 sm=1 tr=0 ts=69b17978 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=FYqZePZFWLRCczkUEhwA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-11_02,2026-03-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 spamscore=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 adultscore=0 clxscore=1015 malwarescore=0 suspectscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603110119 On 3/11/26 08:00, Heiko Carstens wrote: > On Tue, Mar 10, 2026 at 03:02:42PM +0000, Janosch Frank wrote: >> There are special cases where secure storage access exceptions happen >> in a kernel context for pages that don't have the PG_arch_1 bit >> set. That bit is set for non-exported guest secure storage (memory) >> but is absent on storage donated to the Ultravisor since the kernel >> isn't allowed to export donated pages. >> >> Prior to this patch we would try to export the page by calling >> arch_make_folio_accessible() which would instantly return since the >> arch bit is absent signifying that the page was already exported and >> no further action is necessary. This leads to secure storage access >> exception loops which can never be resolved. >> >> With this patch we unconditionally try to export and if that fails we >> fixup. >> >> Fixes: 084ea4d611a3 ("s390/mm: add (non)secure page access exceptions handlers") >> Reported-by: Heiko Carstens >> Suggested-by: Heiko Carstens >> Signed-off-by: Janosch Frank >> --- >> >> Changed fault error handling to nolock. (Heiko) >> Added PG_arch_1 cleanup requested off-list. (Claudio) >> >> --- >> arch/s390/mm/fault.c | 11 +++++++++-- >> 1 file changed, 9 insertions(+), 2 deletions(-) >> >> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c >> index a52aa7a99b6b..191cc53caead 100644 >> --- a/arch/s390/mm/fault.c >> +++ b/arch/s390/mm/fault.c >> @@ -441,10 +441,17 @@ void do_secure_storage_access(struct pt_regs *regs) >> folio = phys_to_folio(addr); >> if (unlikely(!folio_try_get(folio))) >> return; >> - rc = arch_make_folio_accessible(folio); >> + rc = uv_convert_from_secure(folio_to_phys(folio)); >> + if (!rc) >> + clear_bit(PG_arch_1, &folio->flags.f); >> folio_put(folio); > > Isn't the clear_bit() racy? That is: another CPU could make the page secure > again, set (the still set) PG_arch_1, and then clear_bit() removes the bit, > and we end up with a secure page where PG_arch_1 is not set? > Which in turn would arch_make_folio_accessible() al > > Or is that not possible? > > Just wondering, since __make_folio_secure() requires the folio to be locked > when setting PG_arch_1, while clearing happens unlocked. But chances are high > that I don't understand the code. > __make_folio_secure() checks the refcount and if the comments hold true, it should protect us from a flag being set as long as we have the extra reference which we should have gotten via folio_try_get(). It does not protect us from a double clear.