kvm_emulate_cp15_id_reg(9)

💅 kvm_emulate_cp15_id_reg(9) — like, the Kernel API Manual page your bestie actually wants to read 🎀

okay so bestie, welcome to the glow-up of kvm_emulate_cp15_id_reg(9) from the Kernel API Manual ✨ it's a short one but it's lowkey iconic, so grab a strawberry drink 🍓 and let's get into it.

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🌸 NAME 🌸

kvm_emulate_cp15_id_reg — she handles an MRC trap on a guest CP15 access where CRn=0, and that range is literally the AArch32 feature registers. no cap. 💅

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🦋 SYNOPSIS 🦋

int kvm_emulate_cp15_id_reg (struct kvm_vcpu *vcpu , struct
       sys_reg_params *params );

like, that's the whole signature, we love a concise queen 👑

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🎀 ARGUMENTS 🎀

• vcpu — the vCPU pointer. the main character of this function, fr fr. 🫶
• params — the system register access parameters. the supporting cast, but she eats every time. ✨

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🔥 DESCRIPTION 🔥

so here's the tea ☕ — our cp15 system register tables? they do not enumerate the AArch32 feature registers. not even a little. 🙈

but conveniently — and this is the slay part — our AArch64 table does. and the AArch32 system register encoding can be trivially remapped into the AArch64 one for the feature registers, like:

Append op0=3, leaving op1, CRn, CRm, and op2 the same. 💫

that's it. that's the remap. iconic behavior honestly.

now, per DDI0487G.b G7.3.1, paragraph "Behavior of VMSAv8-32 32-bit System registers with (coproc=0b1111, CRn==c0)", read accesses from this range are either UNKNOWN or RES0. so it's giving "whatever, honestly" 💀

but ngl, the rerouting remains architectural — because we treat undefined registers in this range as RAZ. so the vibe check passes and the architecture is respected. periodt. 👑

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🌈 SEE ALSO 🌈

• Kernel file ./arch/arm64/kvm/sys_regs.c
• kvm_handle_cp_64(9)
• kvm_handle_cp10_id(9)
• kvm_handle_cp_32(9)
• emulate_sys_reg(9)
• kvm_reset_sys_regs(9)
• kvm_handle_sys_reg(9)

all of these are her friends, go say hi 🦋💖

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and that's the whole page bestie!! 🧚 this little cutie lives in ./arch/arm64/kvm, dated October 2026, and yes she's got her own kvm_emulate_cp15_id_reg(9) header and footer, we stan a well-formatted queen 💜⭐ mwah, go read more manpages, ily 🎀