Re: [PATCH 1/9] mm: introduce hw_pte_t for PTE table storage
From: Alexander Gordeev <agordeev@linux.ibm.com>
Date: 2026-08-07 07:10:13
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bpf, damon, dri-devel, intel-gfx, linux-arch, linux-fsdevel, linux-mm, linux-perf-users, lkml, xen-devel
On Thu, Aug 06, 2026 at 09:38:39AM +0100, Muhammad Usama Anjum wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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.hdiff --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.hdiff --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 <asm/page.h> + +#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;
quoted hunk ↗ jump to hunk
+#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