On Mon, Oct 01, 2018 at 11:28:17AM +0100, Catalin Marinas wrote:

On Thu, Sep 27, 2018 at 02:48:43PM +0000, Steve Capper wrote:

quoted

On Thu, Sep 27, 2018 at 02:50:32PM +0100, Steve Capper wrote:

quoted

On Fri, Sep 21, 2018 at 06:40:31PM +0100, Catalin Marinas wrote:

quoted

quoted

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 1bdeca8918a6..8449e266cd46 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h

@@ -577,11 +577,21 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
 #define pgd_ERROR(pgd)		__pgd_error(__FILE__, __LINE__, pgd_val(pgd))
 
 /* to find an entry in a page-table-directory */
-#define pgd_index(addr)		(((addr) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
+#define pgd_index(addr, ptrs)		(((addr) >> PGDIR_SHIFT) & ((ptrs) - 1))
+#define _pgd_offset_raw(pgd, addr, ptrs) ((pgd) + pgd_index(addr, ptrs))
+#define pgd_offset_raw(pgd, addr)	(_pgd_offset_raw(pgd, addr, PTRS_PER_PGD))
 
-#define pgd_offset_raw(pgd, addr)	((pgd) + pgd_index(addr))
+static inline pgd_t *pgd_offset(const struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *ret;
+
+	if (IS_ENABLED(CONFIG_ARM64_TRY_52BIT_VA) && (addr < TASK_SIZE))
+		ret = _pgd_offset_raw(mm->pgd, addr, 1ULL << (vabits_user - PGDIR_SHIFT));
+	else
+		ret = pgd_offset_raw(mm->pgd, addr);
 
-#define pgd_offset(mm, addr)	(pgd_offset_raw((mm)->pgd, (addr)))
+	return ret;
+}
 
 /* to find an entry in a kernel page-table-directory */
 #define pgd_offset_k(addr)	pgd_offset(&init_mm, addr)

We can decouple pgd_offset_k() from pgd_offset() and there wouldn't be a
need to check the addr < TASK_SIZE. Do we have any case where
pgd_offset() is used on a kernel address?

Unfortunately there are a few cases where pgd_offset is used instead of
pgd_offset_k, I'll see if I can fix these in a separate patch and that
would then simplify this patch.

So it turns out that __change_memory_common, calls apply_to_page_range
which then calls pgd_offset...

Ah, James Morse had a plan to change apply_to_page_range() for other
reasons but I'm not sure whether that would have helped.

quoted

Is it worth changing __change_memory_common, or would it be better to
introduce a check in pgd_offset (can also check the mm parameter)?

The problem here doesn't seem to be __change_memory_common() but rather
apply_to_page_range(). Since there are other users of this API (e.g.
alloc_vm_area()), I think we should just change pgd_offset(). Would a
check on the (mm == &init_mm) be sufficient? Otherwise, we could do a
test on bit 55 of the address.

Ahh okay, yes I can change pgd_offset to check for init_mm.

Cheers,
-- 
Steve