The following commit has been merged into the x86/mm branch of tip:
Commit-ID: 6eb82f9940267d3af260989d077a2833f588beae
Gitweb: https://git.kernel.org/tip/6eb82f9940267d3af260989d077a2833f588beae
Author: Joerg Roedel <jroedel@xxxxxxx>
AuthorDate: Tue, 21 Jul 2020 11:59:51 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Mon, 27 Jul 2020 12:32:29 +02:00
x86/mm: Pre-allocate P4D/PUD pages for vmalloc area
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 no synchronization of that area is
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 <jroedel@xxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200721095953.6218-2-joro@xxxxxxxxxx
---
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 dbae185..e76bdb0 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);
}
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