Re: [PATCH 5/7] x86/bugs: Only harden syscalls when needed

[Nikolay Borisov]

On 11.04.24 г. 8:40 ч., Josh Poimboeuf wrote:
> Syscall hardening (i.e., converting the syscall indirect branch to a
> series of direct branches) may cause performance regressions in certain
> scenarios.  Only use the syscall hardening when indirect branches are
> considered unsafe.
>
> Fixes: 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

Why fiddle with syscall mechanism if the bhb scrubbing sequence 
mitigates bhb? AFAIU (correct me if I'm wrong) the original idea was to 
have use syscall hardening instead of the BHB sequence but since it 
became clear that's not sufficient bhb scrubbing completely subsumes the 
direct branch approach in the syscall handler?

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