setup_physmem(9)

✨ setup_physmem(9) ✨

okay bestie, welcome to the Kernel API Manual — this one's a kernel-level function from the UML (User-Mode Linux) world, so grab a lil snack and let's get into it 🫶

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🌸 NAME 🌸

setup_physmem — the function that sets up physical memory for UML, no cap 💅

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🦋 SYNOPSIS 🦋

void setup_physmem (unsigned long start , unsigned long reserve_end ,
       unsigned long len );

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🎀 ARGUMENTS 🎀

• start — the start address of the physical kernel memory, aka the start address of the executable image. literally where it all begins ✨
• reserve_end — the end address of the physical kernel memory. that's a wrap 🎬
• len — the length of total physical memory that should be mapped/made available, in bytes. yes, bytes. all of them 💖

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👑 DESCRIPTION 👑

So here's the tea, bestie: this function creates an unlinked temporary file of size (len) and memory maps it on the last executable image address (uml_reserved). iconic behavior honestly 🧚

The offset is needed because the length of the total physical memory (len) includes the size of the memory used by the executable image — but the mapped-to address is the last address of the executable image (where uml_reserved == end address of executable image). it's giving "accounting for the overlap" and it ate 💅

The memory mapped memory of the temporary file is used as backing memory of all user space processes/kernel tasks. so yeah, it's kind of a big deal 🔥

ngl this one's lowkey doing a lot of heavy lifting behind the scenes — the temp file is the memory, fr fr ✨

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💜 SEE ALSO 💜

• Kernel file ./arch/um/kernel/physmem.c — go read the source, bestie, it's right there 🙈

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and that's the whole vibe check! this page came to you from ./arch/um/kernel, dated October 2026 — slay, periodt, go set up some physical memory 🍓💖🎀