On 02/14/2018 10:11 AM, Cornelia Huck wrote: > On Tue, 13 Feb 2018 18:11:05 -0600 > Michael Roth <mdr...@linux.vnet.ibm.com> wrote: > >> This blog entry is intended as a follow-up to the original entry in >> January regarding Spectre/Meltdown and the proposed changes to address >> them in the upcoming 2.11.1 release. >> >> This entry is meant to accompany the 2.11.1 release (planned for >> 2018-02-14) and document how to make use of the new options for >> various architectures. >> >> Cc: Eduardo Habkost <ehabk...@redhat.com> >> Cc: Paolo Bonzini <pbonz...@redhat.com> >> Cc: Peter Maydell <peter.mayd...@linaro.org> >> Cc: Suraj Jitindar Singh <sjitindarsi...@gmail.com> >> Cc: David Gibson <da...@gibson.dropbear.id.au> >> Cc: Christian Borntraeger <borntrae...@de.ibm.com> >> Cc: Cornelia Huck <coh...@redhat.com> >> Cc: Thomas Huth <th...@redhat.com> >> Signed-off-by: Michael Roth <mdr...@linux.vnet.ibm.com> >> --- >> >> The pseries/s390 bits have gotten some initial review (thanks >> Suraj/Christian), >> but it can definitely use some additional review on the x86 side of things. >> >> Also, Peter if think anything extra should to be mentioned on the ARM side >> just >> let me know what to add. >> >> .../2018-02-14-qemu-2-11-1-and-spectre-update.md | 180 >> +++++++++++++++++++++ >> 1 file changed, 180 insertions(+) >> create mode 100644 _posts/2018-02-14-qemu-2-11-1-and-spectre-update.md > > [some comments/questions regarding s390 cpu models, adding DavidH on cc:] > >> +## enabling mitigations for s390 KVM guests >> + >> +For s390 guests there are 2 CPU options relating to Spectre/Meltdown: > > s/options/feature bits/ ? > >> + >> +* bpb: Branch prediction blocking >> +* ppa15: PPA15 is installed >> + >> +**bpb** requires a host kernel patched with: >> + >> + commit 35b3fde6203b932b2b1a5b53b3d8808abc9c4f60 >> + KVM: s390: wire up bpb feature >> + >> +and both **bpb** and **ppa15** require a firmware with the appropriate >> support >> +level as well as guest kernel patches to enable the functionality within >> +guests. Please check with your distro/vendor to confirm. >> + >> +Both **bpb** and **ppa15** are enabled by default with newer/patched host >> +kernels, and can also be set manually. For example: >> + >> + qemu-system-s390x -M s390-ccw-virtio-2.11 ... \ >> + -cpu zEC12,bpb=on,ppa15=on > > Do we also want to add that bpb/ppa15 are on if you use the _full_ > model (as opposed to the _base_ model)? Or is this going into too much > detail about the cpu model?
full model is just an internal implementation. Either use - host passthrough - host model - add bpb and ppa15 manually to the choosen model (e.g. z13,bpb=on,ppa15=on) > >> + >> +WRT to migration, enabling **bpb** requires the source/target also have >> **bpb** > > Either "WRT migration", or "With regard to migration" :) > >> +enabled. Since this is enabled by default, you must ensure that **bpb**=off >> if >> +you wish to maintain migration compatibility with existing guests, or take >> +steps to reboot guests with **bpb** enabled prior to migrating them. > > This paragraph confuses me a bit. Both bpb and ppa15 are guest visible, > aren't they? >