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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> From: Muhammad Usama Anjum Content-Language: en-US In-Reply-To: <3db8233c-3785-444e-b2eb-3e5fc5cb2f17-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: g6sLusA9X41u1ejA18zr5/0Hh+oxjNblxuqvfooYrhKJWuytwsqkYM4RBDsVD6JUPG5ejrRcqnr5/e7tppZJbWyjdo7t0o+y6z68tsoif+F1MBaBmgNHyyctH3CIoA/SkECaXcG16VOwlN9BPUQ0jemKU5fquWEAgHzOiZRFYVgG6EPWjni/TQvwedDSSGb8Razw3w014ZbBUH6R3/c0wWm24LvnYzQv+O7tSwf+LD8ovZuboPDpk0K2qUMKcAzXRFN5Agl8K8bfESJXk4tJL+oyf7av+q6WK2Br07wYwX8iCuY6olsVmayuluAaae4jxdx6l7Rfd0Sxs1FZSgFIEBdpvTlmClNis1jG6i1BiVLn1AWIPxbDqedfdPJx2hH9vhU5ko2RaVILr1JHK4cc51ZlbJ7gAPev9zfv7mGajHlpjSLdLi8QeNSS211id+sa X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Aug 2026 15:24:42.8031 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7b1f1875-57fb-491d-136b-08def4980165 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: DU2PEPF00028D12.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI0PR08MB10800 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? This could have been avoided if each architecture defined its own hw_pte_t. But for now we are keeping the generic definition of hw_pte_t. > >> +#else >> +#define hw_pte_t pte_t >> +#endif >> + >> +#endif /* !__ASSEMBLY__ */ >> + >> +#endif /* _LINUX_PGTABLE_TYPES_H */ >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 331daf7fcfab5..31ba9ebf4aafd 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -1316,6 +1316,9 @@ comment "GUP_TEST needs to have DEBUG_FS enabled" >> config GUP_GET_PXX_LOW_HIGH >> bool >> >> +config ARCH_HAS_HW_PTE_T >> + bool >> + >> config DMAPOOL_TEST >> tristate "Enable a module to run time tests on dma_pool" >> depends on HAS_DMA >> -- >> 2.47.3 >> -- Thanks, Usama