Re: [PATCH v3 9/9] KVM: Move instrumentation-safe annotations for enter/exit to x86 code

[Christian Borntraeger]

On 16.04.21 00:21, Sean Christopherson wrote:
> Drop the instrumentation_{begin,end}() annonations from the common KVM
> guest enter/exit helpers, and massage the x86 code as needed to preserve
> the necessary annotations.  x86 is the only architecture whose transition
> flow is tagged as noinstr, and more specifically, it is the only
> architecture for which instrumentation_{begin,end}() can be non-empty.
>
> No other architecture supports CONFIG_STACK_VALIDATION=y, and s390 is the
> only other architecture that support CONFIG_DEBUG_ENTRY=y.  For
> instrumentation annontations to be meaningful, both aformentioned configs
> must be enabled.
>
> Letting x86 deal with the annotations avoids unnecessary nops by
> squashing back-to-back instrumention-safe sequences.

We have considered implementing objtool for s390. Not sure where we
stand and if we will do this or not. Sven/Heiko?

So maybe drop this patch until every other arch agrees that there are
no plans to implement this.