From: Björn Töpel <bjorn@xxxxxxxxxxxx> The RISC-V port requires that kernel PGD entries are to be synchronized between MMs. This is done via the vmalloc_fault() function, that simply copies the PGD entries from init_mm to the faulting one. Historically, faulting in PGD entries have been a source for both bugs [1], and poor performance. One way to get rid of vmalloc faults is by pre-allocating the PGD entries. Pre-allocating the entries potientially wastes 64 * 4K (65 on SV39). The pre-allocation function is pulled from Jörg Rödel's x86 work, with the addition of 3-level page tables (PMD allocations). The pmd_alloc() function needs the ptlock cache to be initialized (when split page locks is enabled), so the pre-allocation is done in a RISC-V specific pgtable_cache_init() implementation. Pre-allocate the kernel PGD entries for the vmalloc/modules area, but only for 64b platforms. Link: https://lore.kernel.org/lkml/20200508144043.13893-1-joro@xxxxxxxxxx/ # [1] Signed-off-by: Björn Töpel <bjorn@xxxxxxxxxxxx> --- arch/riscv/mm/fault.c | 20 +++------------ arch/riscv/mm/init.c | 58 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 62 insertions(+), 16 deletions(-) diff --git a/arch/riscv/mm/fault.c b/arch/riscv/mm/fault.c index 8685f85a7474..6b0b5e517e12 100644 --- a/arch/riscv/mm/fault.c +++ b/arch/riscv/mm/fault.c @@ -230,32 +230,20 @@ void handle_page_fault(struct pt_regs *regs) return; /* - * Fault-in kernel-space virtual memory on-demand. - * The 'reference' page table is init_mm.pgd. + * Fault-in kernel-space virtual memory on-demand, for 32-bit + * architectures. The 'reference' page table is init_mm.pgd. * * NOTE! We MUST NOT take any locks for this case. We may * be in an interrupt or a critical region, and should * only copy the information from the master page table, * nothing more. */ - if (unlikely((addr >= VMALLOC_START) && (addr < VMALLOC_END))) { + if (!IS_ENABLED(CONFIG_64BIT) && + unlikely(addr >= VMALLOC_START && addr < VMALLOC_END)) { vmalloc_fault(regs, code, addr); return; } -#ifdef CONFIG_64BIT - /* - * Modules in 64bit kernels lie in their own virtual region which is not - * in the vmalloc region, but dealing with page faults in this region - * or the vmalloc region amounts to doing the same thing: checking that - * the mapping exists in init_mm.pgd and updating user page table, so - * just use vmalloc_fault. - */ - if (unlikely(addr >= MODULES_VADDR && addr < MODULES_END)) { - vmalloc_fault(regs, code, addr); - return; - } -#endif /* Enable interrupts if they were enabled in the parent context. */ if (!regs_irqs_disabled(regs)) local_irq_enable(); diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c index 747e5b1ef02d..38bd4dd95276 100644 --- a/arch/riscv/mm/init.c +++ b/arch/riscv/mm/init.c @@ -1363,3 +1363,61 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node, return vmemmap_populate_basepages(start, end, node, NULL); } #endif + +#ifdef CONFIG_64BIT +/* + * Pre-allocates page-table pages for a specific area in the kernel + * page-table. Only the level which needs to be synchronized between + * all page-tables is allocated because the synchronization can be + * expensive. + */ +static void __init preallocate_pgd_pages_range(unsigned long start, unsigned long end, + const char *area) +{ + unsigned long addr; + const char *lvl; + + for (addr = start; addr < end && addr >= start; addr = ALIGN(addr + 1, PGDIR_SIZE)) { + pgd_t *pgd = pgd_offset_k(addr); + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + + lvl = "p4d"; + p4d = p4d_alloc(&init_mm, pgd, addr); + if (!p4d) + goto failed; + + if (pgtable_l5_enabled) + continue; + + lvl = "pud"; + pud = pud_alloc(&init_mm, p4d, addr); + if (!pud) + goto failed; + + if (pgtable_l4_enabled) + continue; + + lvl = "pmd"; + pmd = pmd_alloc(&init_mm, pud, addr); + if (!pmd) + goto failed; + } + return; + +failed: + /* + * The pages have to be there now or they will be missing in + * process page-tables later. + */ + panic("Failed to pre-allocate %s pages for %s area\n", lvl, area); +} + +void __init pgtable_cache_init(void) +{ + preallocate_pgd_pages_range(VMALLOC_START, VMALLOC_END, "vmalloc"); + if (IS_ENABLED(CONFIG_MODULES)) + preallocate_pgd_pages_range(MODULES_VADDR, MODULES_END, "bpf/modules"); +} +#endif base-commit: ac9a78681b921877518763ba0e89202254349d1b -- 2.39.2
