On 9/11/18 4:20 PM, Thomas Gleixner wrote:

On Tue, 11 Sep 2018, Boris Ostrovsky wrote:

...

For unprivileged Xen PV guests this is normal memory and ioremap will not be able to properly map it.

While at it, since ioremap may return NULL, add a test for pointer's validity.

I assume this goes back to very dead kernels, so that should go with a Cc stable, right?

Yes, I forgot to add those (and now I did), thanks for pointing this out.

It has to go at least all the way back to 4.13 since before f7eaf6e00fd58 ("x86/boot: Move EISA setup to a separate file"), just by luck, early_ioremap() worked for the guests.

-boris