[RFC V1 14/16] arm64/mm: Enable fixmap with 5 level page table
From: Anshuman Khandual <hidden>
Date: 2026-02-24 05:13:35
Also in:
linux-mm, lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
Enable fixmap with 5 level page table when required. This creates table entries at the PGD level. Add a fallback stub for pgd_page_paddr() when (PGTBALE_LEVELS <= 4) which helps in intercepting any unintended usage. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Anshuman Khandual <redacted> --- arch/arm64/include/asm/pgtable.h | 1 + arch/arm64/mm/fixmap.c | 18 +++++++++++++++--- 2 files changed, 16 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index b39d3d3c5dfc..0f262a97e320 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h@@ -1215,6 +1215,7 @@ static inline p4d_t *p4d_offset_kimg(pgd_t *pgdp, u64 addr) #else static inline bool pgtable_l5_enabled(void) { return false; } +#define pgd_page_paddr(pgd) ({ BUILD_BUG(); 0; }) #define p4d_index(addr) (((addr) >> P4D_SHIFT) & (PTRS_PER_P4D - 1))
diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
index 4c2f71929777..d6209aff31d0 100644
--- a/arch/arm64/mm/fixmap.c
+++ b/arch/arm64/mm/fixmap.c@@ -34,6 +34,7 @@ static_assert(NR_BM_PMD_TABLES == 1); static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __page_aligned_bss; static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused; static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused; +static p4d_t bm_p4d[PTRS_PER_P4D] __page_aligned_bss __maybe_unused; static inline pte_t *fixmap_pte(unsigned long addr) {
@@ -95,6 +96,19 @@ static void __init early_fixmap_init_pud(p4d_t *p4dp, unsigned long addr, early_fixmap_init_pmd(pudp, addr, end); } +static void __init early_fixmap_init_p4d(pgd_t *pgdp, unsigned long addr, + unsigned long end) +{ + pgd_t pgd = pgdp_get(pgdp); + p4d_t *p4dp; + + if (pgd_none(pgd)) + __pgd_populate(pgdp, __pa_symbol(bm_p4d), + PGD_TYPE_TABLE | PGD_TABLE_AF); + p4dp = p4d_offset_kimg(pgdp, addr); + early_fixmap_init_pud(p4dp, addr, end); +} + /* * The p*d_populate functions call virt_to_phys implicitly so they can't be used * directly on kernel symbols (bm_p*d). This function is called too early to use
@@ -107,9 +121,7 @@ void __init early_fixmap_init(void) unsigned long end = FIXADDR_TOP; pgd_t *pgdp = pgd_offset_k(addr); - p4d_t *p4dp = p4d_offset_kimg(pgdp, addr); - - early_fixmap_init_pud(p4dp, addr, end); + early_fixmap_init_p4d(pgdp, addr, end); } /*
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2.43.0