pfnmap_setup_cachemode(9)

💖 pfnmap_setup_cachemode(9) 💖

okay bestie, welcome to the Kernel API Manual — this one's from the <linux/pgtable.h> girlies and it's lowkey so useful. sit down, grab a strawberry drink 🍓, and let's get into it.

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✨ NAME ✨

pfnmap_setup_cachemode — sets up the cachemode in the pgprot for a pfn range. that's the whole vibe. 🎀

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🌸 SYNOPSIS 🌸

int pfnmap_setup_cachemode (unsigned long pfn , unsigned long size ,
pgprot_t *prot );

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🦋 ARGUMENTS 🦋

• pfn — the start of the pfn range. like, where the range begins, bestie. 📍
• size — the size of the pfn range, and this one's in bytes so don't come at it with pages. ngl this trips people up.
• prot — the pgprot to modify. it's a pointer, so yeah, we're editing it in place. 💅

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👑 DESCRIPTION 👑

so here's the tea: this function looks up the cachemode for the pfn range starting at pfn with the size size, and stores it in prot — leaving the other data in prot unchanged. literally just the cachemode part. don't panic. 🫶

what that means is: a hardware implementation gets fine-grained control of memory cache behavior down to page level granularity. iconic. and if there's no hardware implementation? this function does nothing. yeah. it's a whole ✨no-op✨ moment. 💀

currently there's only one implementation for this — the x86 Page Attribute Table (PAT). see Documentation/arch/x86/pat.rst for more details. iykyk. 📚

⚠️ also she can fail — specifically if the pfn range spans pfns that require differing cachemodes. so heads up. 😭

if the pfn range was previously verified to have a single cachemode, it's sufficient to query only a single pfn. the assumption is that this is the case for drivers using the vmf_insert_pfn*() interface. fr fr, that's the intended use case.

Returns 0 on success and -EINVAL on error. that's it, that's the whole return value situation. 🌈

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⭐ SEE ALSO ⭐

Kernel file ./include/linux/pgtable.h plus this whole bestie lineup:

• lazy_mmu_mode_enable(9)
• lazy_mmu_mode_disable(9)
• __task_lazy_mmu_mode_pause(9)
• lazy_mmu_mode_pause(9)
• __task_lazy_mmu_mode_resume(9)
• lazy_mmu_mode_resume(9)
• pte_batch_hint(9)
• set_ptes(9)
• clear_young_dirty_ptes(9)
• get_and_clear_full_ptes(9)
• get_and_clear_ptes(9)
• clear_full_ptes(9)
• clear_ptes(9)
• clear_nonpresent_ptes(9)
• ptep_try_set(9)
• flush_tlb_before_set(9)
• wrprotect_ptes(9)
• clear_flush_young_ptes(9)
• test_and_clear_young_ptes(9)
• modify_prot_start_ptes(9)
• modify_prot_commit_ptes(9)
• pfnmap_track(9)
• pfnmap_untrack(9)
• pfnmap_setup_cachemode_pfn(9)

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mwah 💋 that's the page! big slay to the <purple>./include/linux</purple> crew, this one's dated October 2026, and remember — cache behavior is a lifestyle, not a phase. 🧚💜