dat_set_cmma_bits(9)

💅 dat_set_cmma_bits — a Kernel API Manual moment

okay bestie, welcome to the Kernel API Manual page for dat_set_cmma_bits(9), and yes you're gonna get it, because this one is genuinely not that deep once we vibe through it 🫶

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✨ NAME ✨

dat_set_cmma_bits — literally here to set the CMMA bits for a whole range of guest pages 💖

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🌸 SYNOPSIS 🌸

int dat_set_cmma_bits (struct kvm_s390_mmu_cache *mc , union asce asce ,
gfn_t gfn , unsigned long count , unsigned long mask , const uint8_t
*bits );

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🎀 ARGUMENTS 🎀

• mc — the cache used for allocations, she's the one holding the bag 💅
• asce — the ASCE of the guest. yep. that's the whole description. iconic of her honestly ✨
• gfn — the guest frame of the first page whose CMMA bits are getting set (the original says "fist" and honestly? typo queen behavior, but she means first 💀)
• count — how many pages need to be processed. do the math, bestie, that's how many 💖
• mask — which PGSTE bits should be set 🎯
• bits — points to an array with the CMMA attributes 🌈

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🦋 DESCRIPTION 🦋

so this function sets the CMMA attributes for the given pages. that's the whole mission, main character energy fr fr 👑

but here's the little plot twist — if the input buffer has zero length, no action is taken. nothing. zip. nada. she simply does not move 🙈 otherwise, the attributes are set and the mm->context.uses_cmm flag is set. so like, if anything happens at all, that flag is coming along for the ride ✨

each byte in bits contains new values for bits 32-39 of the PGSTE. and currently — key word currently — only the fields NT and US are applied. that's the vibe check, and only those two passed 💅

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⭐ RETURN ⭐

• 0 in case of success 🎉
• a negative error value otherwise 😭

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🌈 SEE ALSO 🌈

go off and read these too, iykyk 🧚

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

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lowkey reminder from your girl: no cap, the facts above are the facts. run it, don't run it, that's on you 💖

okay that's the page!! and for the cute sign-off: this little beauty lives in ./arch/s390/kvm/gmap, dated October 2026 — screenshot it, frame it, obsess 💜🎀