Re: [PATCH v2 3/4] software node: verify that property data is not on stack

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Mon, Mar 30, 2026 at 02:49:52PM -0700, Dmitry Torokhov wrote:
> On Mon, Mar 30, 2026 at 01:33:47PM +0300, Andy Shevchenko wrote:
> > On Sun, Mar 29, 2026 at 07:27:50PM -0700, Dmitry Torokhov wrote:

...

> > > +	for (prop = node->properties; prop && prop->name; prop++) {
> > > +		if (!prop->is_inline && object_is_on_stack(prop->pointer)) {
> > 
> > I read more about this... Any code that uses vmalloc() (or potentially may
> > switch to it from regular allocator with help of kvalloc() and similar) will
> > fail now. While it might be no issue right now, this may become a such. So
> > with this check in place you put a requirement that properties can only be
> > allocated from a kernel low memory heap and not vm.
> 
> Can you tell me more about this? As far as I can see it will actually
> have false negatives with CONFIG_VMAP_STACK, but should be OK not
> trigger with vmalloced memory... But I am genuinely interested to know
> more.

I dug into the history of this macro. It was added for the block and ide
subsystems to make sure that there is no buffer supplied that may not be DMAed.
As we know vmalloc():ed buffers may not be DMAed. In some commit messages
it was explicitly mentioned that this macro fails on vmalloc():ed memory.

Note, I haven't checked the actual behaviour by trying that on the HW.

-- 
With Best Regards,
Andy Shevchenko