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Fri, 16 May 2025 17:07:57 +0000 (GMT) Date: Fri, 16 May 2025 19:07:55 +0200 From: Claudio Imbrenda To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, Christian Borntraeger , Janosch Frank , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle , Thomas Huth , Matthew Wilcox , Zi Yan , Sebastian Mitterle Subject: Re: [PATCH v1 0/3] s390/uv: handle folios that cannot be split while dirty Message-ID: <20250516190755.32917d48@p-imbrenda> In-Reply-To: <20250516123946.1648026-1-david@redhat.com> References: <20250516123946.1648026-1-david@redhat.com> Organization: IBM X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: cbLRk8KAcORrniPp6oJAntkKow6roWiN X-Proofpoint-ORIG-GUID: cbLRk8KAcORrniPp6oJAntkKow6roWiN X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNTE2MDE2NyBTYWx0ZWRfX3xqHC4oBj9bo YZYdBu/Paw1MLiE/054CZBnb7aVupy8kUOokX55rXkThUKc6DqCIX4/qSbwmU0L3SIyOoqTROnQ mxKIoQA42qkEUh6VM8NAnLYSdSXq53cu7rjBRViArtPm63dcfWsZc8Tx3XthPQg4p2VD9E6LZ4j dhu/E8LF/TcOZRTlyhaRxAIDlhXnW50twx5/aDlB4oQIC5RZFA+3PUnZJHSgX02kb99IkQGwD/m 9prYMk4clzlIeJ4VAiWqRi9QcakrSqkBjC7eFIkIiTN9PvF66CcjyZEB0rEjAiHMR+MGrrqrBeM +amziRU8KT96wLkfFI1jGVw6w3URX5ag005MocrhZ1y79Hzov3qd7XFHwxqYs3td0W4IFlChVRY T/TR90EACXZGgdZ0HKeEUdSI1zYOzNZKlSFysdn2xTm7/GAOR1qFDHdYv/hkrFASGuCPAegZ X-Authority-Analysis: v=2.4 cv=ZcMdNtVA c=1 sm=1 tr=0 ts=682770f3 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=kj9zAlcOel0A:10 a=dt9VzEwgFbYA:10 a=20KFwNOVAAAA:8 a=VnNF1IyMAAAA:8 a=JfrnYn6hAAAA:8 a=Ikd4Dj_1AAAA:8 a=bI5ggvasLi50PZegio4A:9 a=CjuIK1q_8ugA:10 a=1CNFftbPRP8L7MoqJWF3:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-05-16_05,2025-05-16_03,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 spamscore=0 clxscore=1011 bulkscore=0 priorityscore=1501 mlxlogscore=744 impostorscore=0 mlxscore=0 phishscore=0 suspectscore=0 lowpriorityscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505070000 definitions=main-2505160167 X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2A7B110001A X-Stat-Signature: bdb65sjn4guiycx3yuzbw1nybsixma96 X-HE-Tag: 1747415289-9564 X-HE-Meta: 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 s2rTqLNz KgtDWlHsu0gG6DlvwVnozKyYWVya1KpevIPzdnRTWEh2AXhPdy1oyARgTxhuoZcBj4E6U+AhO4v/eEG5OE6Vs/lJNr73ijFtusWCWkCakA3e6SqmShA6RpSf7kKQqd5CBfDbSd8+Tcz393ooTnxsl3RSkG66BtXhBDjPuPL93x1uno0DcUXyWBlIDQwB0g6eBj4HjDGAOPHco+PDCcGFTiDTPmjf52u61NRWW1rZ47IvqFX1QlT3PB8KWWQ/6BuULHlm9pHL5X4uYbToV1i+kAisnZbQRiJpT8oiBJMyyxJgABU4mC7vp4z/uiYta17hHUXwImamzi3PMlnD8b4jT3RP57Hixh0Me/Nv77eKlA/f8gMeaDKpGGlZAW6KeNkaWOPIFg3n1VlrsfUIP1OaKTazAfv4zcoETCCl+VtI1ViP6dG33Ja2wlyAnocROKPa2JK3C X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 16 May 2025 14:39:43 +0200 David Hildenbrand wrote: > From patch #3: > > " > Currently, starting a PV VM on an iomap-based filesystem with large > folio support, such as XFS, will not work. We'll be stuck in > unpack_one()->gmap_make_secure(), because we can't seem to make progress > splitting the large folio. > > The problem is that we require a writable PTE but a writable PTE under such > filesystems will imply a dirty folio. > > So whenever we have a writable PTE, we'll have a dirty folio, and dirty > iomap folios cannot currently get split, because > split_folio()->split_huge_page_to_list_to_order()->filemap_release_folio() > will fail in iomap_release_folio(). > > So we will not make any progress splitting such large folios. > " > > Let's fix one related problem during unpack first, to then handle such > folios by triggering writeback before immediately trying to split them > again. > > This makes it work on XFS with large folios again. > > Long-term, we should cleanly supporting splitting such folios even > without writeback, but that's a bit harder to implement and not a quick > fix. yet another layer of duck tape I really dislike the current interaction between secure execution and I/O, I hope I can get a cleaner solution as soon as possible meanwhile, let's keep the boat afloat; whole series: Reviewed-by: Claudio Imbrenda David: thanks for fixing this mess! > > Cc: Christian Borntraeger > Cc: Janosch Frank > Cc: Claudio Imbrenda > Cc: David Hildenbrand > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Alexander Gordeev > Cc: Sven Schnelle > Cc: Thomas Huth > Cc: Matthew Wilcox > Cc: Zi Yan > Cc: Sebastian Mitterle > > David Hildenbrand (3): > s390/uv: don't return 0 from make_hva_secure() if the operation was > not successful > s390/uv: always return 0 from s390_wiggle_split_folio() if successful > s390/uv: improve splitting of large folios that cannot be split while > dirty > > arch/s390/kernel/uv.c | 85 ++++++++++++++++++++++++++++++++++++------- > 1 file changed, 72 insertions(+), 13 deletions(-) > > > base-commit: 088d13246a4672bc03aec664675138e3f5bff68c