Re: Xen 4.0 crashes with pvops kernel

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 06/15/2010 02:57 PM, Jan Beulich wrote:
> Actually, that's a difference to non-pv-ops that I strongly
> believe should be fixed: While in the traditional kernel
> __direct_remap_pfn_range() is used to establish I/O memory
> mappings (and hence there is a way to propagate errors), the
> pv-ops kernel appears to use ioremap_page_range() - just like
> native - which can only return -ENOMEM (upon page table
> allocation failure), due to the lack of a return value from
> set_pte_at().
>   

So that ioremap() itself will return an error if Xen prevents a mapping?

> But then again I must be missing something here, since
> xen_set_pte_at() falls back to xen_set_pte() if the hypercall
> it tries first fails, and that one would fault when establishing
> the mapping, not when trying to first use it. Jeremy?
>   

If the pte has _PAGE_IO set (which all ioremap ptes should), then it
will call xen_set_iomap_pte. This can't fail (not return code), so if
the hypercall fails then it will leave it unmapped.  It should at least
print a warn-on in that case.

    J