x86: cpa: simplify locking

further simplify cpa locking: since the largepage-split is a
slowpath, use the pgd_lock for the whole operation, intead
of the mmap_sem.

This also makes it suitable for DEBUG_PAGEALLOC purposes again.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 5 insertions, 7 deletions

diff --git a/arch/x86/mm/pageattr_32.c b/arch/x86/mm/pageattr_32.c
index 0966023dfd70..9cf2fea54eb5 100644
--- a/arch/x86/mm/pageattr_32.c
+++ b/arch/x86/mm/pageattr_32.c
@@ -37,9 +37,8 @@ pte_t *lookup_address(unsigned long address, int *level)
         return pte_offset_kernel(pmd, address);
 }
 
-static void set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
+static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
 {
-        unsigned long flags;
         struct page *page;
 
         /* change init_mm */
@@ -47,7 +46,6 @@ static void set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
         if (SHARED_KERNEL_PMD)
                 return;
 
-        spin_lock_irqsave(&pgd_lock, flags);
         for (page = pgd_list; page; page = (struct page *)page->index) {
                 pgd_t *pgd;
                 pud_t *pud;
@@ -58,12 +56,12 @@ static void set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
                 pmd = pmd_offset(pud, address);
                 set_pte_atomic((pte_t *)pmd, pte);
         }
-        spin_unlock_irqrestore(&pgd_lock, flags);
 }
 
 static int split_large_page(pte_t *kpte, unsigned long address)
 {
         pgprot_t ref_prot = pte_pgprot(pte_clrhuge(*kpte));
+        unsigned long flags;
         unsigned long addr;
         pte_t *pbase, *tmp;
         struct page *base;
@@ -73,7 +71,7 @@ static int split_large_page(pte_t *kpte, unsigned long address)
         if (!base)
                 return -ENOMEM;
 
-        down_write(&init_mm.mmap_sem);
+        spin_lock_irqsave(&pgd_lock, flags);
         /*
          * Check for races, another CPU might have split this page
          * up for us already:
@@ -95,11 +93,11 @@ static int split_large_page(pte_t *kpte, unsigned long address)
         /*
          * Install the new, split up pagetable:
          */
-        set_pmd_pte(kpte, address, mk_pte(base, ref_prot));
+        __set_pmd_pte(kpte, address, mk_pte(base, ref_prot));
         base = NULL;
 
 out_unlock:
-        up_write(&init_mm.mmap_sem);
+        spin_unlock_irqrestore(&pgd_lock, flags);
 
         if (base)
                 __free_pages(base, 0);