dat_crstep_xchg_atomic(9)

📦 version 7.3.1, in nixpkgs unstable

💅 dat_crstep_xchg_atomic(9) — the Kernel API Manual page bestie 🎀

okay so this is a page from the Kernel API Manual, and the star of the show is dat_crstep_xchg_atomic — say it with me, it's a mouthful, but she's iconic for it ✨

🌸 NAME 🌸

dat_crstep_xchg_atomic — atomically exchange a gmap CRSTE with another. literally swap one CRSTE for a different CRSTE and do it atomically, no cap 💅

🦋 SYNOPSIS 🦋

bool dat_crstep_xchg_atomic (union crste *crstep , union crste old ,
union crste new , gfn_t gfn , union asce asce );

she takes five args and comes back at you with a bool, periodt 💖

🎀 ARGUMENTS 🎀

  • crstep — pointer to the CRST entry. like, the actual entry. that's her 🫶
  • old — the expected old value. what you think is sitting there rn 👀
  • new — the replacement entry. the glow-up that's going in 🌈
  • gfn — the affected guest address. yes bestie, this one matters 🗺️
  • asce — the asce of the address space. the address space's asce, exactly as advertised 🧚

✨ DESCRIPTION ✨

k so here's the vibe: this function exists because sometimes you need to atomically exchange a CRSTE that potentially maps a prefix area — and you gotta do it without having to invalidate it inbetween. 😭

like yes, that's the whole reason she's here. no invalidate-in-the-middle situation. she handles it atomically and moves on. main character energy fr fr 👑

🔥 CONTEXT 🔥

this function is assumed to be called with kvm->mmu_lock held. assumed, bestie — so hold that lock like you mean it 🙈

⭐ RETURN ⭐

returns true if the exchange was successful. that's it, that's the tea 💀✨

💜 SEE ALSO 💜

kernel file ./arch/s390/kvm/gmap/dat.c, plus her whole friend group:

go read those too, iykyk 🦋

and that's the page!! this one lives over at ./arch/s390/kvm/gmap, dated October 2026, and she's filed under dat_crstep_xchg_atomic(9) if you ever need to find her again 💖🎀 slay, go hold that lock 🫶

📦 where this page comes from