Re: [PATCH] locking/atomic/x86: Introduce try_cmpxchg64

[Uros Bizjak]

On Tue, May 10, 2022 at 6:55 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, May 10, 2022 at 05:42:17PM +0200, Uros Bizjak wrote:
> > This patch adds try_cmpxchg64 to improve code around cmpxchg8b.  While
> > the resulting code improvements on x86_64 are minor (a compare and a move saved),
> > the improvements on x86_32 are quite noticeable. The code improves from:
>
> What user of cmpxchg64 is this?

This is cmpxchg64 in pi_try_set_control from
arch/x86/kvm/vmx/posted_intr.c, as shown in a RFC patch [1].

There are some more opportunities for try_cmpxchg64 in KVM, namely
fast_pf_fix_direct_spte in arch/x86/kvm/mmu/mmu.c and
tdp_mmu_set_spte_atomic in arch/x86/kvm/mmu/tdp_mmu.c

[1] https://www.spinics.net/lists/kvm/msg266042.html

Uros.