On Tue, Jul 21, 2020 at 11:59:51AM +0200, Joerg Roedel wrote: > From: Joerg Roedel <[email protected]> > > Pre-allocate the page-table pages for the vmalloc area at the level > which needs synchronization on x86-64, which is P4D for 5-level and > PUD for 4-level paging. > > Doing this at boot makes sure all no synchronization of that area is
Nit: ^all can be dropped > necessary at runtime. The synchronization takes the pgd_lock and > iterates over all page-tables in the system, so it can take quite long > and is better avoided. > > Signed-off-by: Joerg Roedel <[email protected]> > --- > arch/x86/mm/init_64.c | 52 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 52 insertions(+) > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index dbae185511cd..e76bdb001460 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -1238,6 +1238,56 @@ static void __init register_page_bootmem_info(void) > #endif > } > > +/* > + * Pre-allocates page-table pages for the vmalloc 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_vmalloc_pages(void) > +{ > + unsigned long addr; > + const char *lvl; > + > + for (addr = VMALLOC_START; addr <= VMALLOC_END; addr = ALIGN(addr + 1, > PGDIR_SIZE)) { > + pgd_t *pgd = pgd_offset_k(addr); > + p4d_t *p4d; > + pud_t *pud; > + > + p4d = p4d_offset(pgd, addr); > + if (p4d_none(*p4d)) { > + /* Can only happen with 5-level paging */ > + p4d = p4d_alloc(&init_mm, pgd, addr); > + if (!p4d) { > + lvl = "p4d"; > + goto failed; > + } > + } > + > + if (pgtable_l5_enabled()) > + continue; > + > + pud = pud_offset(p4d, addr); > + if (pud_none(*pud)) { > + /* Ends up here only with 4-level paging */ > + pud = pud_alloc(&init_mm, p4d, addr); > + if (!pud) { > + lvl = "pud"; > + 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 vmalloc area\n", lvl); > +} > + > void __init mem_init(void) > { > pci_iommu_alloc(); > @@ -1261,6 +1311,8 @@ void __init mem_init(void) > if (get_gate_vma(&init_mm)) > kclist_add(&kcore_vsyscall, (void *)VSYSCALL_ADDR, PAGE_SIZE, > KCORE_USER); > > + preallocate_vmalloc_pages(); > + > mem_init_print_info(NULL); > } > > -- > 2.27.0 > -- Sincerely yours, Mike.
