dat_entry_walk(9)

✨ dat_entry_walk(9) ✨

okay so bestie, welcome to dat_entry_walk — it's a real one from the Kernel API Manual, and it's basically the girl whose whole job is walking the gmap page tables 💅 like she literally strolls through them. no cap. let's get into it 🫶

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🌸 NAME 🌸

dat_entry_walk — walk the gmap page tables. that's it, that's the vibe 🎀

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🦋 SYNOPSIS 🦋

int dat_entry_walk (struct kvm_s390_mmu_cache *mc , gfn_t gfn , union
asce asce , int flags , int walk_level , union crste **last , union pte
**ptepp );

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💖 ARGUMENTS 💖

• mc — the cache she uses to allocate dat tables, if needed. and like, you can literally pass NULL here if neither DAT_WALK_SPLIT nor DAT_WALK_ALLOC is specified in flags. so she doesn't even need it, she's flexible like that ✨
• gfn — the guest frame. yeah. that one.
• asce — the ASCE of the address space 👑
• flags — the flags, from the WALK_* macros. there's a whole lineup of them below, keep reading 💀
• walk_level — the level to walk to, using the LEVEL_* macros.
• last — gets filled with the last visited non-pte DAT entry 🎀
• ptepp — gets filled with the last visited pte entry, if there even is one — otherwise it's NULL. not every walk finds a pte, and that's okay 🙈

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🌈 DESCRIPTION 🌈

so what does she actually do? she returns a table entry pointer for the given guest address and walk_level. that's the whole main character energy of this function, fr fr 💅

and the flags? each one has a meaning, so let's go through them one by one, no skipping, i would never 😤

• DAT_WALK_IGN_HOLES: consider holes as normal table entries. holes are just entries to her, she doesn't judge 🕳️✨
• DAT_WALK_ALLOC: allocate new tables to reach the requested level, if needed.
• DAT_WALK_SPLIT: split existing large pages to reach the requested level, if needed. she will absolutely break up a large page if that's what it takes 💔
• DAT_WALK_LEAF: return successfully whenever a large page is encountered. like, found a big one? we're done here, slay.
• DAT_WALK_ANY: return successfully even if the requested level could not be reached. she's forgiving. she's chill. lowkey iconic.
• DAT_WALK_CONTINUE: walk to the requested level with the specified flags, and then try to continue walking to ptes with only DAT_WALK_ANY. two-step queen behavior 👑
• DAT_WALK_USES_SKEYS: storage keys are in use. noted. logged. tracked. 🔑

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💜 CONTEXT 💜

this one's important bestie, don't skip it: called with kvm->mmu_lock held. like, that's the rule. that's the whole rule. don't be out here calling her without the lock, that's not the move 😭

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🍓 RETURN 🍓

okay so she can come back with a bunch of different things depending on what went down, and you need to know which is which:

• PGM_ADDRESSING if the requested address lies outside memory.
• a PIC number if the requested address lies in a memory hole of type _DAT_TOKEN_PIC.
• -EFAULT if the requested address lies inside a memory hole of a different type.
• -EINVAL if the given ASCE is not compatible with the requested level. mismatch arc 💀
• -EFBIG if the requested level could not be reached because a larger frame was found.
• -ENOENT if the requested level could not be reached for other reasons.
• -ENOMEM if running out of memory while allocating or splitting a table. the classic 😭

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🔥 SEE ALSO 🔥

Kernel file ./arch/s390/kvm/gmap/dat.c dat_crstep_xchg_atomic(9), _dat_walk_gfn_range(9), dat_test_age_gfn(9), dat_perform_essa(9), dat_set_cmma_bits(9)

they're all in the group chat together, go say hi 🫶

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okay and that's the whole page!! this one lives over in ./arch/s390/kvm/gmap, and it's dated October 2026 — so like, mark your calendars bestie 🎀💖✨ slay, bye! 🦋