[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>

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

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
 }
 
 /*

arch/powerpc/mm/pgtable_32.c

@@ -451,3 +451,55 @@ mm_ptov (unsigned long paddr)
 	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 */

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. */
 

include/asm-powerpc/cacheflush.h

@@ -64,6 +64,12 @@ extern void flush_dcache_phys_range(unsigned long start, unsigned long stop);
 	memcpy(dst, src, len)
 
 
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+/* internal debugging function */
+void kernel_map_pages(struct page *page, int numpages, int enable);
+#endif
+
 #endif /* __KERNEL__ */
 
 #endif /* _ASM_POWERPC_CACHEFLUSH_H */