Re: 4level page tables for Linux

[Dave Hansen <haveblue@us.ibm.com>]

@@ -110,13 +115,18 @@ int install_file_pte(struct mm_struct *m
                unsigned long addr, unsigned long pgoff, pgprot_t prot)
 {
...
+       pml4 = pml4_offset(mm, addr);
+
+       spin_lock(&mm->page_table_lock);
+       pgd = pgd_alloc(mm, pml4, addr);
+       if (!pgd)
+               goto err_unlock;

Locking isn't needed for access to the pml4?  This is a wee bit
different from pgd's and I didn't see any documentation about it
anywhere.  Could be confusing.

+++ linux-2.6.9rc4-4level/mm/memory.c 
...
+#undef inline
+#define inline
+unsigned long caddr;

Is this just for debugging?

+static inline void free_one_pml4(struct mmu_gather *tlb, pml4_t *pml4,
+                                unsigned long addr, unsigned long end)
+{
...
+       do {
+               caddr = addr;
+               free_one_pgd(tlb, pgd);
+               free++;
+               addr = (addr + PGDIR_SIZE) & PGDIR_MASK;
+               pgd++;
+       } while (addr && addr < end);

If someone attempts to clear an address which is in the top PGDIR_SIZE
bytes of memory, this will overflow.  Is that an issue?

There also seems to be quite a bit of churn in the copy_*_range()
functions that isn't completely related to the pml4 changes.  Should
that get broken out?

-- Dave