[POWERPC] DEBUG_PAGEALLOC for 32-bit

Here's an implementation of DEBUG_PAGEALLOC for ppc32. It disables BAT
mapping and is only tested with Hash table based processor though it
shouldn't be too hard to adapt it to others.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

 arch/powerpc/Kconfig.debug       |    9 ++++++
 arch/powerpc/mm/init_32.c        |    4 +++
 arch/powerpc/mm/pgtable_32.c     |   52 +++++++++++++++++++++++++++++++++++++++
 arch/powerpc/mm/ppc_mmu_32.c     |    4 ++-
 include/asm-powerpc/cacheflush.h |    6 ++++
 5 files changed, 74 insertions(+), 1 deletion(-)
Signed-off-by: Paul Mackerras <paulus@samba.org>

4 files changed, 68 insertions, 1 deletions

diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 50f48f0c5630..0f8bb86995b4 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -18,6 +18,15 @@ config DEBUG_STACK_USAGE
 
           This option will slow down process creation somewhat.
 
+config DEBUG_PAGEALLOC
+        bool "Debug page memory allocations"
+        depends on DEBUG_KERNEL && !SOFTWARE_SUSPEND && PPC32
+        help
+          Unmap pages from the kernel linear mapping after free_pages().
+          This results in a large slowdown, but helps to find certain types
+          of memory corruptions.
+
+
 config HCALL_STATS
         bool "Hypervisor call instrumentation"
         depends on PPC_PSERIES && DEBUG_FS
diff --git a/arch/powerpc/mm/init_32.c b/arch/powerpc/mm/init_32.c
index 0e53ca8f02fb..5fce6ccecb8d 100644
--- a/arch/powerpc/mm/init_32.c
+++ b/arch/powerpc/mm/init_32.c
@@ -115,6 +115,10 @@ void MMU_setup(void)
         if (strstr(cmd_line, "noltlbs")) {
                 __map_without_ltlbs = 1;
         }
+#ifdef CONFIG_DEBUG_PAGEALLOC
+        __map_without_bats = 1;
+        __map_without_ltlbs = 1;
+#endif
 }
 
 /*
diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
index f75f2fc7bc7e..8a2fc16ee0a7 100644
--- a/arch/powerpc/mm/pgtable_32.c
+++ b/arch/powerpc/mm/pgtable_32.c
@@ -451,3 +451,55 @@ exit:
         return ret;
 }
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
+
+static int __change_page_attr(struct page *page, pgprot_t prot)
+{
+        pte_t *kpte;
+        pmd_t *kpmd;
+        unsigned long address;
+
+        BUG_ON(PageHighMem(page));
+        address = (unsigned long)page_address(page);
+
+        if (v_mapped_by_bats(address) || v_mapped_by_tlbcam(address))
+                return 0;
+        if (!get_pteptr(&init_mm, address, &kpte, &kpmd))
+                return -EINVAL;
+        set_pte_at(&init_mm, address, kpte, mk_pte(page, prot));
+        wmb();
+        flush_HPTE(0, address, pmd_val(*kpmd));
+        pte_unmap(kpte);
+
+        return 0;
+}
+
+/*
+ * Change the page attributes of an page in the linear mapping.
+ *
+ * THIS CONFLICTS WITH BAT MAPPINGS, DEBUG USE ONLY
+ */
+static int change_page_attr(struct page *page, int numpages, pgprot_t prot)
+{
+        int i, err = 0;
+        unsigned long flags;
+
+        local_irq_save(flags);
+        for (i = 0; i < numpages; i++, page++) {
+                err = __change_page_attr(page, prot);
+                if (err)
+                        break;
+        }
+        local_irq_restore(flags);
+        return err;
+}
+
+
+void kernel_map_pages(struct page *page, int numpages, int enable)
+{
+        if (PageHighMem(page))
+                return;
+
+        change_page_attr(page, numpages, enable ? PAGE_KERNEL : __pgprot(0));
+}
+#endif /* CONFIG_DEBUG_PAGEALLOC */
diff --git a/arch/powerpc/mm/ppc_mmu_32.c b/arch/powerpc/mm/ppc_mmu_32.c
index 7cceb2c44cb9..05066674a7a0 100644
--- a/arch/powerpc/mm/ppc_mmu_32.c
+++ b/arch/powerpc/mm/ppc_mmu_32.c
@@ -85,8 +85,10 @@ unsigned long __init mmu_mapin_ram(void)
         unsigned long max_size = (256<<20);
         unsigned long align;
 
-        if (__map_without_bats)
+        if (__map_without_bats) {
+                printk(KERN_DEBUG "RAM mapped without BATs\n");
                 return 0;
+        }
 
         /* Set up BAT2 and if necessary BAT3 to cover RAM. */