Over on Twitter, I said:

One unpleasant effect of MDS is that old Intel-based machines (ones with CPUs that will not get microcode updates) are now effectively useless to us, unlike before, because it's been decided that the security risks are too high for almost everything we use machines for. If Intel releases all of the MDS microcode updates they've promised to do (sometime), this will have only a small impact on our available servers. If they decide not to update some older CPUs they're currently promising updates for, we could lose a significant number of servers.

To have MDS mitigated at all on Intel CPUs, you need updated microcode (and to turn off hyperthreading, and an updated kernel; see eg Ubuntu's MDS page). According to people who have carefully gone through the CPU lists available in PDFs that are linked from Intel's MDS advisory page, Intel is definitely not releasing microcode updates for anything older than the 2nd generation 'Core' "Sandy Bridge" architecture, which started appearing in 2011 or so (so in theory my 2011 home machine could receive a microcode update and be fixed against MDS). In theory they are going to release microcode updates for everything since then.

For reasons beyond the scope of this entry, we have decided that we have almost no roles where we are comfortable deploying an unpatchable machine that is vulnerable to MDS. In normal places this might not be an issue, since they would long since have turned over old server hardware. We are not a normal place; we run hardware into the ground, which means that we often have very old servers. For example, up until we reached this decision about MDS, we were still using Dell 1950s as scratch and test machines.

In theory, the direct effects of MDS on our stock of live servers are modest but present; we're losing a few machines, including one quite nice one (a Westmere Xeon with 512 GB of RAM), and some machines that were on the shelf are now junk. However, at the moment we have a significant number of servers that are based around Sandy Bridge Xeons. Intel has promised microcode updates for these CPUs but has not yet delivered them. If Intel never delivers updated microcode, we'll lose a significant number of machines and pretty much decimate the compute infrastructure we provide to the department.

(A great deal of our current compute machines are donated Dell C6220 blades with Xeon E5-2680s, specifically CPUID 206D7 ones. Don't ask how much work it took to get the raw CPUID values that Intel puts in their PDF.)

If further significant MDS related attacks get discovered and Intel is more restricted with microcode updates, this situation will get worse. We have a significant number of in-service Dell R210 IIs and R310 IIs, and they are almost as old as these C6220s (although some of them have Ivy Bridge generation CPUs instead of Sandy Bridge ones). Losing these would really hurt.

(In general we are not very happy with Intel right now, and we are starting to deploy AMD-based machines where we can. I would be happy if someone started offering decent basic 1U or 2U AMD-based servers at competitive prices.)