x86: CPA fix pagetable split

Move the readout of the large entry into the spinlock section to
prevent an unlikely but possible race.

Mark the pmd/pud entry present after the split. We preserved the
non present bit in the new split mapping.

Remove the stale gfp_flags double initialization.

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

1 files changed, 7 insertions, 3 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 74446ea23ffb..72880993af89 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -336,7 +336,7 @@ out_unlock:
 
 static int split_large_page(pte_t *kpte, unsigned long address)
 {
-        pgprot_t ref_prot = pte_pgprot(pte_clrhuge(*kpte));
+        pgprot_t ref_prot;
         gfp_t gfp_flags = GFP_KERNEL;
         unsigned long flags, addr, pfn;
         pte_t *pbase, *tmp;
@@ -344,7 +344,6 @@ static int split_large_page(pte_t *kpte, unsigned long address)
         unsigned int i, level;
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
-        gfp_flags = __GFP_HIGH | __GFP_NOFAIL | __GFP_NOWARN;
         gfp_flags = GFP_ATOMIC | __GFP_NOWARN;
 #endif
         base = alloc_pages(gfp_flags, 0);
@@ -368,6 +367,7 @@ static int split_large_page(pte_t *kpte, unsigned long address)
 #ifdef CONFIG_X86_32
         paravirt_alloc_pt(&init_mm, page_to_pfn(base));
 #endif
+        ref_prot = pte_pgprot(pte_clrhuge(*kpte));
 
         /*
          * Get the target pfn from the original entry:
@@ -377,13 +377,17 @@ static int split_large_page(pte_t *kpte, unsigned long address)
                 set_pte(&pbase[i], pfn_pte(pfn, ref_prot));
 
         /*
-         * Install the new, split up pagetable. Important detail here:
+         * Install the new, split up pagetable. Important details here:
          *
          * On Intel the NX bit of all levels must be cleared to make a
          * page executable. See section 4.13.2 of Intel 64 and IA-32
          * Architectures Software Developer's Manual).
+         *
+         * Mark the entry present. The current mapping might be
+         * set to not present, which we preserved above.
          */
         ref_prot = pte_pgprot(pte_mkexec(pte_clrhuge(*kpte)));
+        pgprot_val(ref_prot) |= _PAGE_PRESENT;
         __set_pmd_pte(kpte, address, mk_pte(base, ref_prot));
         base = NULL;