[MODERATED] Re: ***UNCHECKED*** Re: [PATCH v5 08/11] TAAv5 8

On Tue, Oct 15, 2019 at 12:34:54PM +0200, speck for Michal Hocko wrote:
> OK, so what about this patch on top of Pawan's series? I have to say I am not
> really entirely happy about yet another config option. In principle this
> is not much different from the HT where we decided to stay enabled even
> though it is vulnerable to side channels. But I do understand that much
> more people will notice HT off than TSX off.
> 
> Anyway here is the patch
> ---
> From 9666e91b63cd6213d362d04289e1bcbbe2050bc3 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <[email protected]>
> Date: Tue, 15 Oct 2019 11:21:01 +0200
> Subject: [PATCH] x86, tsx: allow to set tsx=auto by a config option
> 
> There is a general consensus that TSX usage is not largely spread while
> the history shows there is a non trivial space for side channel attacks
> possible. Therefore the tsx is disabled by default even on platforms
> that might have a safe implementation of TSX according to the current
> knowledge. This is a fair trade off to make.
> 
> There are, however, workloads that really do benefit from using TSX and
> updating to a newer kernel with TSX disabled might introduce a
> noticeable regressions. This would be especially a problem for Linux
> distributions which will provide TAA mitigations.
> 
> Introduce X86_INTEL_ENABLE_SAFE_TSX config option to override the
> default tsx=off semantic and make tsx=auto a default which is more
> update friendly.
> 
> Suggested-by: Borislav Petkov <[email protected]>
> Signed-off-by: Michal Hocko <[email protected]>

Since all (or most?) modern Intel CPUs are vulnerable to TAA, defaulting
to tsx=auto would effectively be the same as defaulting to tsx=off,
right?  How does this help with regressions?

-- 
Josh