[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Ping²: [PATCH] x86/PV: conditionally avoid raising #GP for early guest MSR accesses

On 05.02.21 14:00, Jan Beulich wrote:
On 05.02.2021 11:56, Jürgen Groß wrote:
As we need to consider backports of processor bug mitigations
in old guests, too, I think we need to have a "catch-all"

Not being able to run an old updated guest until we add handling
for a new MSR isn't a viable option IMO.

I'm not sure I follow you here: Such backports should still make
use of the respective CPUID bits, and hence shouldn't contain
"blind" MSR accesses. And if there's really something needing to
probe an MSR, then I'd expect such a backport to make sure the
probing actually works in a prereq (presumably) backport.

We know that Linux partially relies on blind MSR accesses to be
tolerated on bare metal. With this and older Xen versions having
worked by _not_ faulting when the guest accesses illegal MSRs
it is not that unlikely that some guests will suddenly fail to

Especially when backporting processor bug mitigations I could
envision not all distros will thoroughly test the kernel to still
run as PV guest on newest Xen.


Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: application/pgp-keys

Attachment: OpenPGP_signature
Description: OpenPGP digital signature



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.