From: Dave Hansen Date: Mon, 14 Apr 2025 17:32:37 +0000 (-0700) Subject: x86/mm: Always tell core mm to sync kernel mappings X-Git-Tag: v6.16-rc1~195^2~26^2~6 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=eb9c7f00f22d6ea2a94e00eb4f33a79064681564;p=thirdparty%2Fkernel%2Flinux.git x86/mm: Always tell core mm to sync kernel mappings Each mm_struct has its own copy of the page tables. When core mm code makes changes to a copy of the page tables those changes sometimes need to be synchronized with other mms' copies of the page tables. But when this synchronization actually needs to happen is highly architecture and configuration specific. In cases where kernel PMDs are shared across processes (SHARED_KERNEL_PMD) the core mm does not itself need to do that synchronization for kernel PMD changes. The x86 code communicates this by clearing the PGTBL_PMD_MODIFIED bit cleared in those configs to avoid expensive synchronization. The kernel is moving toward never sharing kernel PMDs on 32-bit. Prepare for that and make 32-bit PAE always set PGTBL_PMD_MODIFIED, even if there is no modification to synchronize. This obviously adds some synchronization overhead in cases where the kernel page tables are being changed. Signed-off-by: Dave Hansen Link: https://lore.kernel.org/all/20250414173237.EC790E95%40davehans-spike.ostc.intel.com --- diff --git a/arch/x86/include/asm/pgtable-3level_types.h b/arch/x86/include/asm/pgtable-3level_types.h index 9d5b257d44e3c..9759fa0eb6a33 100644 --- a/arch/x86/include/asm/pgtable-3level_types.h +++ b/arch/x86/include/asm/pgtable-3level_types.h @@ -29,7 +29,7 @@ typedef union { #define SHARED_KERNEL_PMD (!static_cpu_has(X86_FEATURE_PTI)) -#define ARCH_PAGE_TABLE_SYNC_MASK (SHARED_KERNEL_PMD ? 0 : PGTBL_PMD_MODIFIED) +#define ARCH_PAGE_TABLE_SYNC_MASK PGTBL_PMD_MODIFIED /* * PGDIR_SHIFT determines what a top-level page table entry can map