[PATCH] powerpc: Add missing icache flushes for hugepages

On most powerpc CPUs, the dcache and icache are not coherent so
between writing and executing a page, the caches must be flushed.
Userspace programs assume pages given to them by the kernel are icache
clean, so we must do this flush between the kernel clearing a page and
it being mapped into userspace for execute. We were not doing this
for hugepages, this patch corrects the situation.

We use the same lazy mechanism as we use for normal pages, delaying
the flush until userspace actually attempts to execute from the page
in question.

Tested on G5.

Signed-off-by: David Gibson <[e-mail]>
Signed-off-by: Paul Mackerras <[e-mail]>

arch/powerpc/mm/hash_utils_64.c

···
 	/* Handle hugepage regions */
 	if (unlikely(in_hugepage_area(mm->context, ea))) {
 		DBG_LOW(" -> huge page !\n");
-		return hash_huge_page(mm, access, ea, vsid, local);
+		return hash_huge_page(mm, access, ea, vsid, local, trap);
 	}
 
 	/* Get PTE and page size from page tables */

arch/powerpc/mm/hugetlbpage.c

···
 	return -ENOMEM;
 }
 
+/*
+ * Called by asm hashtable.S for doing lazy icache flush
+ */
+static unsigned int hash_huge_page_do_lazy_icache(unsigned long rflags,
+						  pte_t pte, int trap)
+{
+	struct page *page;
+	int i;
+
+	if (!pfn_valid(pte_pfn(pte)))
+		return rflags;
+
+	page = pte_page(pte);
+
+	/* page is dirty */
+	if (!test_bit(PG_arch_1, &page->flags) && !PageReserved(page)) {
+		if (trap == 0x400) {
+			for (i = 0; i < (HPAGE_SIZE / PAGE_SIZE); i++)
+				__flush_dcache_icache(page_address(page+i));
+			set_bit(PG_arch_1, &page->flags);
+		} else {
+			rflags |= HPTE_R_N;
+		}
+	}
+	return rflags;
+}
+
 int hash_huge_page(struct mm_struct *mm, unsigned long access,
-		   unsigned long ea, unsigned long vsid, int local)
+		   unsigned long ea, unsigned long vsid, int local,
+		   unsigned long trap)
 {
 	pte_t *ptep;
 	unsigned long old_pte, new_pte;
···
 	rflags = 0x2 | (!(new_pte & _PAGE_RW));
  	/* _PAGE_EXEC -> HW_NO_EXEC since it's inverted */
 	rflags |= ((new_pte & _PAGE_EXEC) ? 0 : HPTE_R_N);
+	if (!cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
+		/* No CPU has hugepages but lacks no execute, so we
+		 * don't need to worry about that case */
+		rflags = hash_huge_page_do_lazy_icache(rflags, __pte(old_pte),
+						       trap);
 
 	/* Check if pte already has an hpte (case 2) */
 	if (unlikely(old_pte & _PAGE_HASHPTE)) {

include/asm-powerpc/mmu.h

···
 			   unsigned int local);
 struct mm_struct;
 extern int hash_huge_page(struct mm_struct *mm, unsigned long access,
-			  unsigned long ea, unsigned long vsid, int local);
+			  unsigned long ea, unsigned long vsid, int local,
+			  unsigned long trap);
 
 extern void htab_finish_init(void);
 extern int htab_bolt_mapping(unsigned long vstart, unsigned long vend,