(Disclaimer: I work at AWS, but I am not linking this in any sort of official capacity. I don't know any more details beyond what is listed in that bulletin, and can't answer any questions related to this, unfortunately.)
"Meanwhile, we suggest using the stronger security and isolation properties of EC2 instances to separate any untrusted workloads."
with:
"Google Compute Engine employs host isolation features which ensure that an individual core is never concurrently shared between distinct virtual machines. This isolation also ensures that, in the case that different virtual machines are scheduled sequentially, the L1 data cache is completely flushed to ensure that no vulnerable state remains."
The former does not inspire confidence. Given the hypervisor on EC2 is opaque to me, I'm not sure how I'm supposed to avoid co-tenanting in a risky fashion.
https://aws.amazon.com/ec2/instance-types/ includes a note that provides some additional information about when vCPUs utilize Intel HT Technology: Each vCPU is a hyperthread of an Intel Xeon core except for T2 and m3.medium. (emphasis added)
https://aws.amazon.com/ec2/virtualcores/ provides a table of the number of cores allocated per instance. Notice that an instance like m5.large that has 2 vCPUs and 1 core. An instance like t2.small has 1 vCPU and 1 core.
Disclosure: I work for AWS
> If it’s a timesliced core, then it’s not what they say they’re selling (a hyperthread).
vs.
_msw_:
> A core can be sequentially time sliced between customer instances when you use a fractional (m3.medium) or burst (T2 instances) CPU instance type.
AWS instance types page ( https://aws.amazon.com/ec2/instance-types/ ):
> Each vCPU is a hyperthread of an Intel Xeon core except for T2 and m3.medium.
Who cares how Google defines things?
It would.
So those cores won't be used optimally. No big deal.
"Meanwhile, we suggest using the stronger security and isolation properties of EC2 instances to separate any untrusted workloads." As I read it, it is talking about running code within your instance - if you have untrusted workloads, rather run them in a separate instance, so as not to encounter issues like this cross-process.
The "strong isolation of EC2 instances" refers to the properties of isolation provided by EC2's virtualization compared to processes within an operating system. It is challenging to safely and securely run untrusted code within sandboxes and processes using general purpose software. However, the hypervisor and hardware based virtualization of EC2 instances is engineered to provide isolation between mutually untrusted instances.
There are several reasons that customers may want to use dedicated instances or dedicated hosts, so we provide those tenancy options as well. The most common reason customers use dedicated hosts so that they can bring their own software licenses, which are often tied to a physical host.
Disclosure: I work for AWS.
In Linux, at least, the Xen hypervisor on EC2 exposes some information about itself at /sys/hypervisor. In particular, I think /sys/hypervisor/uuid would allow you to detect co-tenanting (between two VMs of your own).
Not saying that I think you should do that, or that'd I'd want to — it'd be a PITA to coordinate amongst VMs, and I'm not sure it would matter (what if you're co-tentant w/ a malicious VM? even if you detect it, how do you get out of it?). That is, inside the VM seems like wholly the wrong place to attempt to deal with this. But I don't think many people realize /sys/hypervisor exists.