Annotations/info from the upstream discussion:
The kernel would set OSXSAVE in CR4 when the cpuid bits for XSAVE and
OSXSAVE are set. Xen is supposed to mask those off (cannot say since
which version but it is claimed to be done for quite a while now). The
issues with upstream kernels happened after kernel code for Xen did try
to probe for the feature on its own by writing CR4:
commit 191216b9289ed02256086e6bab4f668112109399
xen: mask XSAVE from cpuid
This was added in 2.6.30 but then replaced by the following two patches
in 2.6.39:
commit 61f4237d5b005767a76f4f3694e68e6f78f392d9
xen: just completely disable XSAVE
commit 947ccf9c3c30307b774af3666ee74fcd9f47f646
xen: Allow PV-OPS kernel to detect whether XSAVE is supported
So kernels newer than 2.6.39 (Oneiric, Precise, Quantal) should be ok
even without the work-around. For Lucid we either should update the
work-around, or (probably the preferred way) backport at least "xen:
just completely disable XSAVE".
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https://bugs.launchpad.net/bugs/1044550
Title:
Update the EC2 work-around for the OSXSAVE issue in pv-ops
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