Re: [PATCH 0/1] x86: restore the write back cache of reserved RAM in iounmap()

[Christoph Hellwig]

On Thu, Nov 19, 2020 at 12:59:01PM -0500, Andrea Arcangeli wrote:
> Hello everyone,
> 
> We identified some PCD set on the direct mapping causing hardly
> reproducible performance issues and this patch fixes the ultimate root
> cause.
> 
> The caller for now has been tweaked to avoid triggering this case (now
> that we know about it)

What is the callers?  The whole SetPageReservered + ioremap* thing
you mention in the actual patch is completely bogus.  I think we'll
need to reject that as well and fix the caller.