Re: [gentoo-user] Re: old kernels are installed during the upgrade

[Wols Lists]

On 02/01/18 22:58, Adam Carter wrote:
> AMD coder's patch to disable the new code (to avoid the performance hit)
> where he states the issue doesnt exist on AMD processors;
> https://lkml.org/lkml/2017/12/27/2

Read LWN, specifically the links to the people who covered the bug.

It's a flaw in speculative forward processing, where the security does
not travel with the speculative processing. So user code can trigger a
page fault that references kernel code, causing that page to be
retrieved. OOPPSSSS. AMD keeps security context with the code, causing
an attempt to exploit the bug to fail with "invalid security context".

And as I understand it the code can be disabled with either a compile
time option or command line switch to the kernel. The relevant code is
called KAISER, which forces kernel and user address space into different
contexts, and causes a nasty context-switching overhead on both Intel
and AMD cpus.

Cheers,
Wol