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Re: [Qemu-devel] [qemu-web PATCH v2] Add a blog post documenting Spectre
From: |
Cornelia Huck |
Subject: |
Re: [Qemu-devel] [qemu-web PATCH v2] Add a blog post documenting Spectre/Meltdown options for QEMU 2.11.1 |
Date: |
Wed, 14 Feb 2018 17:38:58 +0100 |
On Wed, 14 Feb 2018 10:12:13 -0600
Michael Roth <address@hidden> 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 <address@hidden>
> Cc: Paolo Bonzini <address@hidden>
> Cc: Peter Maydell <address@hidden>
> Cc: Suraj Jitindar Singh <address@hidden>
> Cc: David Gibson <address@hidden>
> Cc: Christian Borntraeger <address@hidden>
> Cc: Cornelia Huck <address@hidden>
> Cc: Thomas Huth <address@hidden>
> Cc: Bruce Rogers <address@hidden>
> Cc: Daniel P. Berrangé <address@hidden>
> Cc: David Hildenbrand <address@hidden>
> Signed-off-by: Michael Roth <address@hidden>
> ---
> v2:
> * s/by itself that/by itself for that/ (Bruce)
> * make example formats more consistent (Bruce)
> * clarify wording WRT to host-side security (Daniel, Paolo)
> * general wording/formatting fix-ups (Thomas)
> * s/options/feature bits/ (Cornelia)
> * clarify s390x CPU feature defaults (Thomas/Cornelia/Christian/David)
> * clarify s390x migration compatibility statement (Cornelia)
>
> Thank you for the review!
Thank you for writing this blog post!
>
> .../2018-02-14-qemu-2-11-1-and-spectre-update.md | 190
> +++++++++++++++++++++
> 1 file changed, 190 insertions(+)
> create mode 100644 _posts/2018-02-14-qemu-2-11-1-and-spectre-update.md
> +## Enabling mitigation features for s390x KVM guests
> +
> +For s390x guests there are 2 CPU feature bits relating to Spectre/Meltdown:
> +
> +* 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
> +
> +Both **bpb** and **ppa15** are enabled by default when using "-cpu host"
> +and when the host kernels supports these facilities. For other CPU
> +models, the flags have to be set manually. For example:
> +
> + qemu-system-s390x -M s390-ccw-virtio-2.11 ... \
> + -cpu zEC12,bpb=on,ppa15=on
> +
> +With regard to migration, enabling **bpb** or **ppa15** feature flags
> requires
> +that the source/target also those flags enabled.
s/also those/also has those/
> Since this is enabled by
> +default for '-cpu host' (when available on the host), you must ensure that
> +**bpb**=off,**ppa15**=off is used if you wish to maintain migration
> +compatibility with existing guests when using '-cpu host', or take steps to
> +reboot guests with **bpb**/**ppa15** enabled prior to migration.
Otherwise, s390 part looks good to me.