Comment by Roritharr

Okay, so many tennants are on the same BigQuery/Dynamo machine sharing cores.

If the API is "SQLish queries", I have a hard time believing you are going to be able to trigger these kind of attacks. You need a tight loop of carefully constructed code to flip them, no?

>If the only real solution is to turn off HT/SMT that, seen positively, should net us a lot faster VMs then...

you also doubled the cost of each VM (in terms of cpu), but you didn't double the performance of each VM, so it's a net negative.

If you render websites that run code in your VM (e.g., you're running a traditional shared hosting infrastructure where mutually-untrusted users can upload PHP scripts, or you're doing something serverless / FaaS / Cloudflare Workers / etc. where mutually-untrusted users can upload functions), then yes. If you're rendering websites in the sense of hosting WordPress for lots of people but not permitting custom plugins, then no.

Makes sense. I sure would like some custom processors. :-)

I think EC2 has isolated cores (except t1/t2/t3) all along.

You could run the entire free tier there and disable it for paying customers - I'm sure there's a significant fraction of Amazon and Google's clouds, at least, that are on the free tier, and saving money on those would help everyone (they'd let people who aren't yet at a significant enough scale to care about security play around with things for free, and they'd let the cloud providers pack them very tightly).

Indeed, the idea of "Security" is not negotiable when marketing.

Imagine buying a car that says, "Save $5000 for a less safe version without airbags." Yes, I know Airbags are DOT requirement, just trying to make a point.

Edit: I think people are missing my point. I am not saying they don't sell cheaper models that are less safe. My point is that they don't ACTIVELY market them as such. Point me to an advertisement that says "Save $5000 for a less safe car!". This is in the spirit of what the GP was talking about whether cloud providers can market as "Less secure but cheaper HT option".

For private databases, sure, but I don't need that security if I am running an isolated server that only hosts public data.

Here's lstopo output on a 4-core AWS instance to illustrate your point: https://instaguide.io/info.html?type=c5.xlarge#tab=lstopo

You mean it's random then, right? I mean let's talk about what a hyperthread really is: It's the left over functional units (or execution units).

Say you have 100 adders, the processor tries to schedule as many instructions as it can on those 100 adders, but eventually it will run into data dependencies. The left over units can go to a hyperthread.

My understanding (let me know if I'm wrong) is that Hyperthread aware OSes (which is like what, everything since WinXP/Linux kernel 2.4?) will schedule lower priority tasks to the logical cores and higher priority tasks to the real cores.

So when it comes to a hosted provider (a.k.a cloud provider, a.k.a somebody else's computer), what you get pretty much depends on the virtualisation layer they use: Vmware, KVM, Xen, Hyper-V, etc.

Do hypervisors typically peg VMs to a real physical core? I was always under the impression they over-provision on most hosts, so you're getting part of a core and the vCPUs the list in the product documents just indicates your priority and how may vCPUs appear to your particular VM.