[Xen-changelog] [xen-unstable] [LINUX][PAE] Improve allocation strategy when PAE pgdirs must be below 4GB.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 8070050cc30f3d969835d7b1d6eda57959d56842
# Parent  5552bc2c3716e9e0f57dbba80f61332b895a0f2a
[LINUX][PAE] Improve allocation strategy when PAE pgdirs must be below 4GB.
Moving the re-allocation to low memory into pgd_alloc() has several
advantages:
 1. Avoids race with save/restore where pgdir may end up above 4GB after
    save/restore.
 2. If pgdir cannot be re-allocated we can return failure to the caller
    rather than BUG().
 3. Slightly reduces diff against native Linux code.
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
---
 linux-2.6-xen-sparse/arch/i386/mm/init-xen.c    |    2 
 linux-2.6-xen-sparse/arch/i386/mm/pgtable-xen.c |   57 ++++++++++++++++--------
 2 files changed, 40 insertions(+), 19 deletions(-)

diff -r 5552bc2c3716 -r 8070050cc30f 
linux-2.6-xen-sparse/arch/i386/mm/init-xen.c
--- a/linux-2.6-xen-sparse/arch/i386/mm/init-xen.c      Wed Jun 14 11:19:53 
2006 +0100
+++ b/linux-2.6-xen-sparse/arch/i386/mm/init-xen.c      Wed Jun 14 12:36:06 
2006 +0100
@@ -763,7 +763,7 @@ void __init pgtable_cache_init(void)
 #endif
                                0,
                                pgd_ctor,
-                               pgd_dtor);
+                               PTRS_PER_PMD == 1 ? pgd_dtor : NULL);
        if (!pgd_cache)
                panic("pgtable_cache_init(): Cannot create pgd cache");
 }
diff -r 5552bc2c3716 -r 8070050cc30f 
linux-2.6-xen-sparse/arch/i386/mm/pgtable-xen.c
--- a/linux-2.6-xen-sparse/arch/i386/mm/pgtable-xen.c   Wed Jun 14 11:19:53 
2006 +0100
+++ b/linux-2.6-xen-sparse/arch/i386/mm/pgtable-xen.c   Wed Jun 14 12:36:06 
2006 +0100
@@ -300,11 +300,6 @@ void pgd_ctor(void *pgd, kmem_cache_t *c
        unsigned long flags;
 
        if (PTRS_PER_PMD > 1) {
-               if (!xen_feature(XENFEAT_pae_pgdir_above_4gb)) {
-                       int rc = xen_create_contiguous_region(
-                               (unsigned long)pgd, 0, 32);
-                       BUG_ON(rc);
-               }
                if (HAVE_SHARED_KERNEL_PMD)
                        clone_pgd_range((pgd_t *)pgd + USER_PTRS_PER_PGD,
                                        swapper_pg_dir + USER_PTRS_PER_PGD,
@@ -320,26 +315,22 @@ void pgd_ctor(void *pgd, kmem_cache_t *c
        }
 }
 
+/* never called when PTRS_PER_PMD > 1 */
 void pgd_dtor(void *pgd, kmem_cache_t *cache, unsigned long unused)
 {
        unsigned long flags; /* can be called from interrupt context */
 
-       if (PTRS_PER_PMD > 1) {
-               if (!xen_feature(XENFEAT_pae_pgdir_above_4gb))
-                       xen_destroy_contiguous_region((unsigned long)pgd, 0);
-       } else {
-               spin_lock_irqsave(&pgd_lock, flags);
-               pgd_list_del(pgd);
-               spin_unlock_irqrestore(&pgd_lock, flags);
-
-               pgd_test_and_unpin(pgd);
-       }
+       spin_lock_irqsave(&pgd_lock, flags);
+       pgd_list_del(pgd);
+       spin_unlock_irqrestore(&pgd_lock, flags);
+
+       pgd_test_and_unpin(pgd);
 }
 
 pgd_t *pgd_alloc(struct mm_struct *mm)
 {
        int i;
-       pgd_t *pgd = kmem_cache_alloc(pgd_cache, GFP_KERNEL);
+       pgd_t *pgd_tmp = NULL, *pgd = kmem_cache_alloc(pgd_cache, GFP_KERNEL);
 
        pgd_test_and_unpin(pgd);
 
@@ -363,7 +354,26 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
                        set_pgd(&pgd[i], __pgd(1 + __pa(pmd)));
                }
 
+               /* create_contig_region() loses page data. Make a temp copy. */
+               if (!xen_feature(XENFEAT_pae_pgdir_above_4gb)) {
+                       pgd_tmp = kmem_cache_alloc(pgd_cache, GFP_KERNEL);
+                       if (!pgd_tmp)
+                               goto out_oom;
+                       memcpy(pgd_tmp, pgd, PAGE_SIZE);
+               }
+
                spin_lock_irqsave(&pgd_lock, flags);
+
+               /* Protect against save/restore: move below 4GB with lock. */
+               if (!xen_feature(XENFEAT_pae_pgdir_above_4gb)) {
+                       int rc = xen_create_contiguous_region(
+                               (unsigned long)pgd, 0, 32);
+                       memcpy(pgd, pgd_tmp, PAGE_SIZE);
+                       kmem_cache_free(pgd_cache, pgd_tmp);
+                       if (rc)
+                               goto out_oom;
+               }
+
                for (i = USER_PTRS_PER_PGD; i < PTRS_PER_PGD; i++) {
                        unsigned long v = (unsigned long)i << PGDIR_SHIFT;
                        pgd_t *kpgd = pgd_offset_k(v);
@@ -374,7 +384,9 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
                        make_lowmem_page_readonly(
                                pmd, XENFEAT_writable_page_tables);
                }
+
                pgd_list_add(pgd);
+
                spin_unlock_irqrestore(&pgd_lock, flags);
        }
 
@@ -399,11 +411,15 @@ void pgd_free(pgd_t *pgd)
                        pmd_t *pmd = (void *)__va(pgd_val(pgd[i])-1);
                        kmem_cache_free(pmd_cache, pmd);
                }
+
                if (!HAVE_SHARED_KERNEL_PMD) {
                        unsigned long flags;
                        spin_lock_irqsave(&pgd_lock, flags);
                        pgd_list_del(pgd);
                        spin_unlock_irqrestore(&pgd_lock, flags);
+
+                       pgd_test_and_unpin(pgd);
+
                        for (i = USER_PTRS_PER_PGD; i < PTRS_PER_PGD; i++) {
                                pmd_t *pmd = (void *)__va(pgd_val(pgd[i])-1);
                                make_lowmem_page_writable(
@@ -411,8 +427,13 @@ void pgd_free(pgd_t *pgd)
                                memset(pmd, 0, PTRS_PER_PMD*sizeof(pmd_t));
                                kmem_cache_free(pmd_cache, pmd);
                        }
-               }
-       }
+
+                       if (!xen_feature(XENFEAT_pae_pgdir_above_4gb))
+                               xen_destroy_contiguous_region(
+                                       (unsigned long)pgd, 0);
+               }
+       }
+
        /* in the non-PAE case, free_pgtables() clears user pgd entries */
        kmem_cache_free(pgd_cache, pgd);
 }

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