[MODERATED] Re: [PATCH 5/5] SSB extra v2 5

[Dave Hansen <dave.hansen@linux.intel.com>]

On 05/09/2018 08:36 AM, speck for Thomas Gleixner wrote:
>> For now, it *is* generic, though.  It's whether the mitigation function
>> gets injected into the call path or not.
>>
>> Once we have multiple things we have to mitigate for at entry/exit, we
>> may need to add some other flags to the bpf_prog that say exactly what
>> mitigations we need, like a "bfp_prog->does_memory_write" that
>> explicitly tells us if we need the SSB mitigation.
> Now looking at the overhead of this SSB hardware mitigation stuff I really
> wonder what's the state on investigating software mitigations for BPF.
> 
> The magic PDF talks about that, but has anyone looked at that?

I don't know of anyone that has.  I'm fairly sure no one at Intel has
looked in detail, at least in the post-Spectre timeframe.

Frankly, I think it's mostly a waste of time to do it without having the
BPF folks deeply involved from day one.  They were not fans of the way
we (Intel) did Spectre V1 mitigations and I don't expect this to be any
different.

They were deeply opposed to LFENCE getting used, for instance.