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Bottomley" , Helge Deller , Juergen Gross , Stefano Stabellini , Muchun Song , Oscar Salvador , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Peter Zijlstra , Andrey Ryabinin , David Hildenbrand , Pasha Tatashin , Chris Li , Kairui Song , Uladzislau Rezki , Steven Rostedt , Masami Hiramatsu , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Ingo Molnar , Arnaldo Carvalho de Melo , Namhyung Kim , SJ Park , "Matthew Wilcox (Oracle)" , Jan Kara , Jason Gunthorpe , Leon Romanovsky , Miaohe Lin , Dennis Zhou , Tejun Heo , Christoph Lameter , Mike Rapoport , Johannes Weiner , ziy@nvidia.com, pfalcato@suse.de, ryan.roberts@arm.com, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-parisc@vger.kernel.org, xen-devel@lists.xenproject.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, kasan-dev@googlegroups.com, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, damon@lists.linux.dev Subject: Re: [PATCH 1/9] mm: introduce hw_pte_t for PTE table storage To: Alexander Gordeev References: <20260806083926.1807279-1-usama.anjum@arm.com> <20260806083926.1807279-2-usama.anjum@arm.com> <3db8233c-3785-444e-b2eb-3e5fc5cb2f17-agordeev@linux.ibm.com> <4a42c498-58ca-46f4-819f-da14cfba154f-agordeev@linux.ibm.com> From: Muhammad Usama Anjum Content-Language: en-US In-Reply-To: <4a42c498-58ca-46f4-819f-da14cfba154f-agordeev@linux.ibm.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: VdxhsZ95/ysXP8RdLEbk4sVtvy2edVQtoJ6oqy2f2vUE54Q2Mo9e1tCwYr1WSdLoGGSVNKIFlJyVSKWPQXbElgmtgNyenbdug6KN14JYg/n1wFiCVfUjnkVFmCQDftsy7zeBdBBnFC5apMchrmHRQZW2c4pk7GLTu0UBqctb/bILTt6B+fDXuUyBIpXMP7goDZ5vemuf93YQDFAXgAzq3sHIC/MmP+cXwjQL+mdMBj5uUpP1Tpzb+i5I7It8c5/rJUpJEt/u4e+VT8rJ4jZewcZytBD6B8wAYvh9jGL52VyiptBem5YoT/fKoZXgpzm8ua8C8E2ayqgv67Ld+UAEUGbSEO5TU/TgQuqPotMHI+Yr1drtdridF6rTA0iISMeAQjF/a2rcXho+GZUbep6DokYVrs935fbjMzvhIsItdLEL5z6M19cjFQ/H/YcTSE98 X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Aug 2026 10:10:04.0374 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0add7375-722f-46c6-54e9-08def6c78c07 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM3PEPF0000A79A.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS1PR08MB7538 On 09/08/2026 6:45 pm, Alexander Gordeev wrote: > On Fri, Aug 07, 2026 at 04:24:00PM +0100, Muhammad Usama Anjum wrote: >> On 07/08/2026 8:09 am, Alexander Gordeev wrote: >>> On Thu, Aug 06, 2026 at 09:38:39AM +0100, Muhammad Usama Anjum wrote: >>>> pte_t is used both for logical PTE values and for entries stored in a PTE >>>> table, so pte_t * does not distinguish a pointer to a copied value from a >>>> pointer to table storage. >>>> >>>> Introduce hw_pte_t as the generic name for a PTE table element. Define it >>>> as a macro alias of pte_t by default. When an architecture selects >>>> ARCH_HAS_HW_PTE_T, define it as a structure containing a pte_t instead. >>>> This preserves the representation while allowing converted architectures >>>> to enforce the distinction at compile time. >>>> >>>> Keep the C type definitions behind an __ASSEMBLY__ check because >>>> architecture assembly sources can include this header indirectly. Include >>>> asm/page.h so consumers such as linux/vmalloc.h retain the page definitions >>>> they previously obtained from that header. >>>> >>>> Signed-off-by: Muhammad Usama Anjum >>>> --- >>>> Changes since RFC v1: >>>> - Add the ARCH_HAS_HW_PTE_T opt-in and generic wrapper definition. >>>> - Exclude the C type definitions from assembly sources. >>>> - Update the description for the new opt-in model. >>>> --- >>>> MAINTAINERS | 1 + >>>> include/linux/pgtable_types.h | 17 +++++++++++++++++ >>>> mm/Kconfig | 3 +++ >>>> 3 files changed, 21 insertions(+) >>>> create mode 100644 include/linux/pgtable_types.h >>>> >>>> diff --git a/MAINTAINERS b/MAINTAINERS >>>> index e9c8567308a75..7169bea968cf5 100644 >>>> --- a/MAINTAINERS >>>> +++ b/MAINTAINERS >>>> @@ -16982,6 +16982,7 @@ F: include/linux/mmu_notifier.h >>>> F: include/linux/pagewalk.h >>>> F: include/linux/pgalloc.h >>>> F: include/linux/pgtable.h >>>> +F: include/linux/pgtable_types.h >>>> F: include/linux/ptdump.h >>>> F: include/linux/vmpressure.h >>>> F: include/linux/vmstat.h >>>> diff --git a/include/linux/pgtable_types.h b/include/linux/pgtable_types.h >>>> new file mode 100644 >>>> index 0000000000000..70c3edd00a01b >>>> --- /dev/null >>>> +++ b/include/linux/pgtable_types.h >>>> @@ -0,0 +1,17 @@ >>>> +/* SPDX-License-Identifier: GPL-2.0 */ >>>> +#ifndef _LINUX_PGTABLE_TYPES_H >>>> +#define _LINUX_PGTABLE_TYPES_H >>>> + >>>> +#include >>>> + >>>> +#ifndef __ASSEMBLY__ >>>> + >>>> +#ifdef CONFIG_ARCH_HAS_HW_PTE_T >>>> +typedef struct { pte_t __pte; } hw_pte_t; >>> >>> On s390 it fails to compile once we do typedef hw_pte_t *pgtable_t >>> in asm/page.h. m68k, powerpc and sparc may also have such problem. >>> >>> The below declaration helps to resolve it using forward declaration >>> and without meddling with headers, though I do not like it much: >>> >>> typedef struct __hw_pte_t { pte_t __pte; } hw_pte_t; >> Thank you for testing it out on s390. >> >> As __hw_pte_t isn't being used yet in this series, would s390 enablement >> patches add __hw_pte_t to this definition? > > I hope there is a better solution. As I noted m68k, powerpc and sparc > may also be affected, so I would suggest to look into those as well. > I would prefer s390 to use the generic one rather than circumvent a > compile error in a custom way. I've just checked all of these architectures by doing dirty conversion and reached to same conclusion that __hw_pte_t must be defined like: typedef struct __hw_pte_t { pte_t __pte; } hw_pte_t; I'lll add __hw_pte_t to this series. (Initially on last email I'd thought that the first user would add __hw_pte_t. But it seems sensible to add it now) -- Thanks, Usama