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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Dec 2025 09:14:54.8307 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9c4c0213-dd4e-4f79-f0eb-08de3af13ed5 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: DB1PEPF000509F0.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV1PR08MB10956 X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D4D421C000E X-Stat-Signature: q7ka7nuqd5af1k7xuemd35d4iduwz5ki X-HE-Tag: 1765703703-177439 X-HE-Meta: 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 St1PUhvR 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Brendan, > On Sat, 13 Dec 2025 at 01:18, Yeoreum Yun wrote: > > > > linear_map_split_to_ptes() and __kpti_install_ng_mappings() > > are called as callback of stop_machine(). > > That means these functions context are preemption disabled. > > > > Unfortunately, under PREEMPT_RT, the pagetable_alloc() or > > __get_free_pages() couldn't be called in this context > > since spin lock that becomes sleepable on RT, > > potentially causing a sleep during page allocation. > > > > To address this, pagetable_alloc_nolock(). > > > > Signed-off-by: Yeoreum Yun > > --- > > arch/arm64/mm/mmu.c | 23 ++++++++++++++++++----- > > 1 file changed, 18 insertions(+), 5 deletions(-) > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > index 2ba01dc8ef82..0e98606d8c4c 100644 > > --- a/arch/arm64/mm/mmu.c > > +++ b/arch/arm64/mm/mmu.c > > @@ -475,10 +475,15 @@ static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys, > > 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); > > + struct ptdesc *ptdesc; > > phys_addr_t pa; > > > > + /* Page is zeroed by init_clear_pgtable() so don't duplicate effort. */ > > + if (gfpflags_allow_spinning(gfp)) > > + ptdesc = pagetable_alloc(gfp & ~__GFP_ZERO, 0); > > + else > > + ptdesc = pagetable_alloc_nolock(gfp & ~__GFP_ZERO, 0); > > + > > if (!ptdesc) > > return INVALID_PHYS_ADDR; > > > > @@ -869,6 +874,7 @@ static int __init linear_map_split_to_ptes(void *__unused) > > unsigned long kstart = (unsigned long)lm_alias(_stext); > > unsigned long kend = (unsigned long)lm_alias(__init_begin); > > int ret; > > + gfp_t gfp = IS_ENABLED(CONFIG_PREEMPT_RT) ? __GFP_HIGH : GFP_ATOMIC; > > > > /* > > * Wait for all secondary CPUs to be put into the waiting area. > > @@ -881,9 +887,9 @@ static int __init linear_map_split_to_ptes(void *__unused) > > * PTE. The kernel alias remains static throughout runtime so > > * can continue to be safely mapped with large mappings. > > */ > > - ret = range_split_to_ptes(lstart, kstart, GFP_ATOMIC); > > + ret = range_split_to_ptes(lstart, kstart, gfp); > > if (!ret) > > - ret = range_split_to_ptes(kend, lend, GFP_ATOMIC); > > + ret = range_split_to_ptes(kend, lend, gfp); > > if (ret) > > panic("Failed to split linear map\n"); > > flush_tlb_kernel_range(lstart, lend); > > @@ -1207,7 +1213,14 @@ static int __init __kpti_install_ng_mappings(void *__unused) > > remap_fn = (void *)__pa_symbol(idmap_kpti_install_ng_mappings); > > > > if (!cpu) { > > - alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order); > > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) > > + alloc = (u64) pagetable_alloc_nolock(__GFP_HIGH | __GFP_ZERO, order); > > + else > > + alloc = __get_free_pages(GFP_ATOMIC | __GFP_ZERO, order); > > + > > + if (!alloc) > > + panic("Failed to alloc kpti_ng_pgd\n"); > > + > > I don't have the context on what this code is doing so take this with > a grain of salt, but... > > The point of the _nolock alloc is to give the allocator an excuse to > fail. Panicking on that failure doesn't seem like a great idea to me? I thought first whether it changes to "static" memory area to handle this in PREEMPT_RT. But since this function is called while smp_cpus_done(). So, I think it's fine since there wouldn't be a contention for memory allocation in this phase. Thanks. -- Sincerely, Yeoreum Yun