Testing Intel FSGSBASE Patches For Helping Elevate Linux Performance

[arQon]

You're nearly ALWAYS "just 1 or 2 registers short" in every loop, no matter how many registers you have. :P And the same is even more true for a compiler.

AFAICT, this is all just the KERNEL impact of freeing up those registers, isn't it? So while that's one part of the equation, and clearly of remarkable value on that side alone just from save/restore impact (substantially more than I would have expected, which makes me wonder if I haven't misunderstood things) the other side is rebuilding the userspace with the knowledge that it has 2 more registers available. Or is that already included in these benchmarks after all and I just missed where Michael noted it?

[hotaru]

It clearly was enabled if you knew how to read the flags that were posted on the first page of the article.

it clearly wasn't. full mitigation means spectre_v2=on spec_store_bypass_disable=on l1tf=full,force, as well as compiling the entire system with LVI mitigations. none of that "conditional" or "via prctl and seccomp" shit.

[phuclv]

One thing I haven't seen is whether Windows already handles FSGSBASE?

Windows has supported FSGSBASE since Windows 8.1. You can see the _readfsbase*/_readgsbase_*/_writefsbase*/_writegsbase* functions in the intrinsic list of VS 2015

[phuclv]

You mentioned in one of your other articles that the work on FSGSBASE had attracted interest from Microsoft, which I take to mean that they haven't already implemented it:

https://www.phoronix.com/scan.php?pa...-Linux-Patches

nope. Windows has supported FSGSBASE since Windows 8.1. The fact that MS pushes some changes for Linux's FSGSBASE support has nothing to do with Windows support