Re: [libvirt] [PATCH 0/5] Use non-blacklisted family/model/stepping for Haswell CPU model
* Eduardo Habkost (ehabkost(a)redhat.com) wrote:
A recent glibc commit[1] added a blacklist to ensure it won't
use
TSX on hosts that are known to have a broken TSX implementation.
Our existing Haswell CPU model has a blacklisted
family/model/stepping combination, so it has to be updated to
make sure guests will really use TSX. This is done by patch 5/5.
However, to do this safely we need to ensure the host CPU is not
a blacklisted one, so we won't mislead guests by exposing
known-to-be-good FMS values on a known-to-be-broken host. This is
done by patch 3/5.
I'd just like to mke sure I understand the way this will fail in a migration;
lets say we have a guest that doesn't have the new libc and hosts
with a blacklisted CPU, and -cpu Haswell.
If I understand correctly then:
a) With 'enforce' the destination qemu will fail to start
printing an error about the host lack of tsx feature.
b) Without 'enforce' the destination will start but print
the same error as a warning, but the guest will probably
break as soon as it tries to use a tsx feature?
Any other combination?
Dave
[1]
https://sourceware.org/git/?p=glibc.git;a=commit;h=2702856bf45c82cf8e69f2...
---
Cc: dgilbert(a)redhat.com
Cc: fweimer(a)redhat.com
Cc: carlos(a)redhat.com
Cc: triegel(a)redhat.com
Cc: berrange(a)redhat.com
Cc: jdenemar(a)redhat.com
Cc: pbonzini(a)redhat.com
Eduardo Habkost (5):
i386: Add explicit array size to x86_cpu_vendor_words2str()
i386: host_vendor_fms() helper function
i386/kvm: Blacklist TSX on known broken hosts
pc: Add 2.9 machine-types
i386: Change stepping of Haswell to non-blacklisted value
include/hw/i386/pc.h | 6 ++++++
target/i386/cpu.h | 1 +
hw/i386/pc_piix.c | 15 ++++++++++++---
hw/i386/pc_q35.c | 13 +++++++++++--
target/i386/cpu.c | 32 ++++++++++++++++++++++----------
target/i386/kvm.c | 17 +++++++++++++++++
6 files changed, 69 insertions(+), 15 deletions(-)
--
2.11.0.259.g40922b1
--
Dr. David Alan Gilbert / dgilbert(a)redhat.com / Manchester, UK