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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Jan 2026 16:15:36.0641 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ac0368ea-d7c6-4f71-da4b-08de4a1a29a8 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: DB5PEPF00014B98.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR08MB5453 Hi Ryan, > > linear_map_split_to_ptes() currently allocates page tables while > > splitting the linear mapping into PTEs under stop_machine() using GFP_ATOMIC. > > > > This is fine for non-PREEMPT_RT configurations. > > However, it becomes problematic on PREEMPT_RT, because > > generic memory allocation/free APIs (e.g. pgtable_alloc(), __get_free_pages(), etc.) > > cannot be called from a non-preemptible context, except for the _nolock() variants. > > This is because generic memory allocation/free paths are sleepable, > > as they rely on spin_lock(), which becomes sleepable on PREEMPT_RT. > > > > In other words, even calling pgtable_alloc() with GFP_ATOMIC is not permitted > > in __linear_map_split_to_pte() when it is executed by the stopper thread, > > where preemption is disabled on PREEMPT_RT. > > > > To address this, the required number of page tables is first collected > > and preallocated, and the preallocated page tables are then used > > when splitting the linear mapping in __linear_map_split_to_pte(). > > > > Fixes: 3df6979d222b ("arm64: mm: split linear mapping if BBML2 unsupported on secondary CPUs") > > Signed-off-by: Yeoreum Yun > > Looks good from my perspective. > > I have a couple more small comments below. With those addressed: > > Reviewed-by: Ryan Roberts > > > --- > > arch/arm64/mm/mmu.c | 204 +++++++++++++++++++++++++++++++++++--------- > > 1 file changed, 166 insertions(+), 38 deletions(-) > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > index 4b4908ae189b..cc086e91a506 100644 > > --- a/arch/arm64/mm/mmu.c > > +++ b/arch/arm64/mm/mmu.c > > @@ -529,18 +529,14 @@ static void early_create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys, > > panic("Failed to create page tables\n"); > > } > > > > -static phys_addr_t __pgd_pgtable_alloc(struct mm_struct *mm, gfp_t gfp, > > - enum pgtable_type pgtable_type) > > -{ > > - /* Page is zeroed by init_clear_pgtable() so don't duplicate effort. */ > > - struct ptdesc *ptdesc = pagetable_alloc(gfp & ~__GFP_ZERO, 0); > > - phys_addr_t pa; > > - > > - if (!ptdesc) > > - return INVALID_PHYS_ADDR; > > - > > - pa = page_to_phys(ptdesc_page(ptdesc)); > > +static struct ptdesc **split_pgtables; > > +static unsigned long split_pgtables_count; > > +static unsigned long split_pgtables_idx; > > I think these could all be __initdata, if you make > pgd_pgtable_get_preallocated() __init (see below) ? I don't think so since range_split_to_ptes() couldn't be __init. That's why there is warning while compiling below: WARNING: modpost: vmlinux: section mismatch in reference: range_split_to_ptes+0x3c (section: .text) -> pgd_pgtable_get_preallocated (section: .init.text) > > > > > +static __always_inline void __pgd_pgtable_init(struct mm_struct *mm, > > Is there a reason for __always_inline? If not, I think it's preferable to just > leave it static and let the compiler decide. Okay. I'll remove __always_inline. Thanks. > > > + struct ptdesc *ptdesc, > > + enum pgtable_type pgtable_type) > > +{ > > switch (pgtable_type) { > > case TABLE_PTE: > > BUG_ON(!pagetable_pte_ctor(mm, ptdesc)); > > @@ -555,26 +551,49 @@ static phys_addr_t __pgd_pgtable_alloc(struct mm_struct *mm, gfp_t gfp, > > pagetable_p4d_ctor(ptdesc); > > break; > > } > > - > > - return pa; > > } > > > > -static phys_addr_t > > -pgd_pgtable_alloc_init_mm_gfp(enum pgtable_type pgtable_type, gfp_t gfp) > > +static phys_addr_t __pgd_pgtable_alloc(struct mm_struct *mm, > > + enum pgtable_type pgtable_type) > > { > > - return __pgd_pgtable_alloc(&init_mm, gfp, pgtable_type); > > + /* Page is zeroed by init_clear_pgtable() so don't duplicate effort. */ > > + struct ptdesc *ptdesc = pagetable_alloc(GFP_PGTABLE_KERNEL & ~__GFP_ZERO, 0); > > + > > + if (!ptdesc) > > + return INVALID_PHYS_ADDR; > > + > > + __pgd_pgtable_init(mm, ptdesc, pgtable_type); > > + > > + return page_to_phys(ptdesc_page(ptdesc)); > > } > > > > -static phys_addr_t __maybe_unused > > +static phys_addr_t > > pgd_pgtable_alloc_init_mm(enum pgtable_type pgtable_type) > > { > > - return pgd_pgtable_alloc_init_mm_gfp(pgtable_type, GFP_PGTABLE_KERNEL); > > + return __pgd_pgtable_alloc(&init_mm, pgtable_type); > > } > > > > static phys_addr_t > > pgd_pgtable_alloc_special_mm(enum pgtable_type pgtable_type) > > { > > - return __pgd_pgtable_alloc(NULL, GFP_PGTABLE_KERNEL, pgtable_type); > > + return __pgd_pgtable_alloc(NULL, pgtable_type); > > +} > > + > > +static phys_addr_t > > +pgd_pgtable_get_preallocated(enum pgtable_type pgtable_type) > > I think this could probably be __init? See above. > > > +{ > > + struct ptdesc *ptdesc; > > + > > + if (WARN_ON(split_pgtables_idx >= split_pgtables_count)) > > + return INVALID_PHYS_ADDR; > > + > > + ptdesc = split_pgtables[split_pgtables_idx++]; > > + if (!ptdesc) > > + return INVALID_PHYS_ADDR; > > + > > + __pgd_pgtable_init(&init_mm, ptdesc, pgtable_type); > > + > > + return page_to_phys(ptdesc_page(ptdesc)); > > } > > > > static void split_contpte(pte_t *ptep) > > @@ -586,7 +605,9 @@ static void split_contpte(pte_t *ptep) > > __set_pte(ptep, pte_mknoncont(__ptep_get(ptep))); > > } > > > > -static int split_pmd(pmd_t *pmdp, pmd_t pmd, gfp_t gfp, bool to_cont) > > +static int split_pmd(pmd_t *pmdp, pmd_t pmd, > > + pgtable_alloc_t pgtable_alloc, > > + bool to_cont) > > nit: this will easily fit in 2 lines and still be within 80 chars: Okay. I'll change it. > > static int split_pmd(pmd_t *pmdp, pmd_t pmd, pgtable_alloc_t pgtable_alloc, > bool to_cont) > > > { > > pmdval_t tableprot = PMD_TYPE_TABLE | PMD_TABLE_UXN | PMD_TABLE_AF; > > unsigned long pfn = pmd_pfn(pmd); > > @@ -595,7 +616,7 @@ static int split_pmd(pmd_t *pmdp, pmd_t pmd, gfp_t gfp, bool to_cont) > > pte_t *ptep; > > int i; > > > > - pte_phys = pgd_pgtable_alloc_init_mm_gfp(TABLE_PTE, gfp); > > + pte_phys = pgtable_alloc(TABLE_PTE); > > if (pte_phys == INVALID_PHYS_ADDR) > > return -ENOMEM; > > ptep = (pte_t *)phys_to_virt(pte_phys); > > @@ -630,7 +651,9 @@ static void split_contpmd(pmd_t *pmdp) > > set_pmd(pmdp, pmd_mknoncont(pmdp_get(pmdp))); > > } > > > > -static int split_pud(pud_t *pudp, pud_t pud, gfp_t gfp, bool to_cont) > > +static int split_pud(pud_t *pudp, pud_t pud, > > + pgtable_alloc_t pgtable_alloc, > > + bool to_cont) > > nit: same comment. Thanks for your review :D BTW, except the __init related comments, Could I add R-b tag after fixing others? -- Sincerely, Yeoreum Yun