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Re: [Xen-devel] XSA-60 - how to get back to a sane state



On 12/02/2013 02:28 PM, Jan Beulich wrote:
All,

Jinsong's patches having been in for nearly a month now, but not
being in a shape that would make releasing in 4.4 or backporting to
the older trees desirable, we need to come to a conclusion on
which way to go. Currently it looks like we have three options, but
of course I'll be happy to see other (better!) ones proposed.

1) Stay with what we have.

2) Revert 86d60e85 ("VMX: flush cache when vmentry back to UC
guest") in its entirety plus, perhaps, the change 62652c00 ("VMX:
fix cr0.cd handling") did to vmx_ctxt_switch_to().

3) Apply the attached patch that Andrew and I have been putting
together, with the caveat that it's still incomplete (see below).

The latter two are based on the observation that the amount of
cache flushing we do with what is in the master tree right now is
more than what we did prior to that patch series but still
insufficient. Hence the revert would get us back to the earlier
state (and obviously eliminate the performance problems that
were observed when doing too eager flushing), whereas
applying the extra 5th patch would get us closer to a proper
solution.

What's missing is a description of the pros and cons of 1 and 2. Do you have any links to threads describing the problem?

 -George


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