Re: dom0 PV looping on search_pre_exception_table()

[Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>]

On Thu, Dec 10, 2020 at 05:18:39PM +0000, Andrew Cooper wrote:
> The debugging earlier shows that MMUEXT_SET_LDT has indeed been called. 
> Presumably 0xffffbd000000a000 is a plausible virtual address for NetBSD
> to position the LDT?

Yes, it is. 

> 
> However, Xen finds the mapping not-present when trying to demand-map it,
> hence why the #PF is forwarded to the kernel.
> 
> The way we pull guest virtual addresses was altered by XSA-286 (released
> not too long ago despite its apparent age), but *should* have been no
> functional change.  I wonder if we accidentally broke something there. 
> What exactly are you running, Xen-wise, with the 4.13 version?

It is 4.13.2, with the patch for XSA351

> 
> Given that this is init failing, presumably the issue would repro with
> the net installer version too?

Hopefully yes, maybe even as a domU. But I don't have a linux dom0 to test.

If you have a Xen setup you can test with
http://ftp.netbsd.org/pub/NetBSD/NetBSD-9.1/amd64/binary/kernel/netbsd-INSTALL_XEN3_DOMU.gz

note that this won't boot as a dom0 kernel.

-- 
Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
     NetBSD: 26 ans d'experience feront toujours la difference
--