On Fri, Nov 18, 2016 at 10:42:56AM -0800, Laura Abbott wrote:

On 11/18/2016 09:53 AM, Mark Rutland wrote:

quoted

On Thu, Nov 17, 2016 at 05:16:56PM -0800, Laura Abbott wrote:

quoted

quoted

+#define __virt_to_phys_nodebug(x) ({					\
 	phys_addr_t __x = (phys_addr_t)(x);				\
-	__x & BIT(VA_BITS - 1) ? (__x & ~PAGE_OFFSET) + PHYS_OFFSET :	\
-				 (__x - kimage_voffset); })
+	((__x & ~PAGE_OFFSET) + PHYS_OFFSET);				\
+})

Given the KASAN failure, and the strong possibility that there's even
more stuff lurking in common code, I think we should retain the logic to
handle kernel image addresses for the timebeing (as x86 does). Once
we've merged DEBUG_VIRTUAL, it will be easier to track those down.

Agreed. I might see about adding another option DEBUG_STRICT_VIRTUAL
for catching bad __pa vs __pa_symbol usage and keep DEBUG_VIRTUAL for
catching addresses that will work in neither case.

I think it makes sense for DEBUG_VIRTUAL to do both, so long as the
default behaviour (and fallback after a WARN for virt_to_phys()) matches
what we currently do. We'll get useful diagnostics, but a graceful
fallback.

I think the helpers I suggested below do that?  Or have I misunderstood,
and you mean something stricter (e.g. checking whether a lm address is
is backed by something)?

quoted

phys_addr_t __virt_to_phys(unsigned long x)
{
	WARN(!__is_lm_address(x),
	     "virt_to_phys() used for non-linear address: %pK\n",
	     (void*)x);
	
	return __virt_to_phys_nodebug(x);
}
EXPORT_SYMBOL(__virt_to_phys);

quoted

phys_addr_t __phys_addr_symbol(unsigned long x)
{
	/*
	 * This is bounds checking against the kernel image only.
	 * __pa_symbol should only be used on kernel symbol addresses.
	 */
	VIRTUAL_BUG_ON(x < (unsigned long) KERNEL_START ||
		       x > (unsigned long) KERNEL_END);

	return __pa_symbol_nodebug(x);
}
EXPORT_SYMBOL(__phys_addr_symbol);

Thanks,
Mark.