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Wed, 22 Jan 2025 07:49:56 +0000 (GMT) Date: Wed, 22 Jan 2025 08:49:54 +0100 From: Heiko Carstens To: Alexander Gordeev Cc: Kevin Brodsky , linux-mm@kvack.org, Andrew Morton , Catalin Marinas , Dave Hansen , Linus Walleij , Andy Lutomirski , Peter Zijlstra , "Mike Rapoport (IBM)" , Ryan Roberts , Thomas Gleixner , Will Deacon , Matthew Wilcox , Qi Zheng , linux-alpha@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-um@lists.infradead.org, loongarch@lists.linux.dev, x86@kernel.org Subject: Re: [PATCH v2 6/6] mm: Introduce ctor/dtor at PGD level Message-ID: <20250122074954.8685-A-hca@linux.ibm.com> References: <20250103184415.2744423-1-kevin.brodsky@arm.com> <20250103184415.2744423-7-kevin.brodsky@arm.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: qTola2ylJwUaTSt4IdPRfZSdT02Tio3Q X-Proofpoint-GUID: qTola2ylJwUaTSt4IdPRfZSdT02Tio3Q X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-01-22_03,2025-01-22_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1011 lowpriorityscore=0 mlxlogscore=674 priorityscore=1501 bulkscore=0 spamscore=0 malwarescore=0 phishscore=0 suspectscore=0 mlxscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2411120000 definitions=main-2501220053 On Tue, Jan 21, 2025 at 05:37:33PM +0100, Alexander Gordeev wrote: > On Fri, Jan 03, 2025 at 06:44:15PM +0000, Kevin Brodsky wrote: > > Hi Kevin, > ... > > diff --git a/arch/s390/include/asm/pgalloc.h b/arch/s390/include/asm/pgalloc.h > > index 5fced6d3c36b..b19b6ed2ab53 100644 > > --- a/arch/s390/include/asm/pgalloc.h > > +++ b/arch/s390/include/asm/pgalloc.h > > @@ -130,11 +130,18 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd) > > > > static inline pgd_t *pgd_alloc(struct mm_struct *mm) > > { > > - return (pgd_t *) crst_table_alloc(mm); > > + unsigned long *table = crst_table_alloc(mm); > > + > > + if (!table) > > + return NULL; > > I do not know status of this series, but FWIW, this call is missed: > > crst_table_init(table, _REGION1_ENTRY_EMPTY); Why is that missing? A pgd table can be a Region1, Region2, or Region3 table. The only caller of this function is mm_init() via mm_alloc_pgd(); and right after mm_alloc_pgd() there is a call to init_new_context() which will initialize the pgd correctly. I guess what really gets odd, and might be broken (haven't checked yet) is what happens on dynamic upgrade of page table levels (->crst_table_upgrade()). With that a pgd may become a pud, and with that we get an imbalance with the ctor/dtor calls for the various page table levels when they get freed again. Plus, at first glance, it looks also broken that we have open-coded crst_alloc() calls instead of using the "proper" page table allocation API within crst_table_upgrade(), which again would cause an imbalance.