Andrew - I hope the explanation below resolves your query about the header include (in [0]), let me know if doing this as a series like this works (we need to enforce the ordering here). Thanks! [0]: 20250514153648.598bb031a2e498b1ac505b60@xxxxxxxxxxxxxxxxxxxx Currently, when somebody attempts to set MADV_NOHUGEPAGE on a system that does not enable CONFIG_TRANSPARENT_HUGEPAGE the confguration option, this results in an -EINVAL error arising. This doesn't really make sense, as to do so is essentially a no-op. Additionally, the semantics of setting VM_[NO]HUGEPAGE in any case are such that, should the attribute not apply, nothing will be done. It therefore makes sense to simply make this operation a noop. However, a fly in the ointment is that, in order to do so, we must check against the MADV_NOHUGEPAGE constant. In doing so, we encounter two rather annoying issues. The first is that the usual include we would import to get hold of MADV_NOHUGEPAGE, linux/mman.h, results in a circular dependency: * If something includes linux/mman.h, we in turn include linux/mm.h prior to declaring MADV_NOHUGEPAGE. * This then, in turn, includes linux/huge_mm.h. * linux/huge_mm.h declares hugepage_madvise(), which then tries to reference MADV_NOHUGEPAGE, and the build fails. This can be reached in other ways too. So we work around this by including uapi/asm/mman.h instead, which allows us to keep hugepage_madvise() inline. The second issue is that the s390 arch declares PROT_NONE as a value in the enum prot_type enumeration. By updating the include in linux/huge_mm.h, we pull in the PROT_NONE declaration (unavoidably, this is ultimately in uapi/asm-generic/mman-common.h alongside MADV_NOHUGEPAGE), which collides with the enumeration value. To resolve this, we rename PROT_NONE to PROT_TYPE_DUMMY. The ordering of these patches is critical, the s390 patch must be applied prior to the MADV_NOHUGEPAGE patch, and therefore the two patches are sent as a series. v1: * Place patches in series. * Correct typo in comment as per James. previous patches: huge_mm.h patch - https://lore.kernel.org/all/20250508-madvise-nohugepage-noop-without-thp-v1-1-e7ceffb197f3@xxxxxxxx/ s390 patch - https://lore.kernel.org/all/20250514163530.119582-1-lorenzo.stoakes@xxxxxxxxxx/ Ignacio Moreno Gonzalez (1): mm: madvise: make MADV_NOHUGEPAGE a no-op if !THP Lorenzo Stoakes (1): KVM: s390: rename PROT_NONE to PROT_TYPE_DUMMY arch/s390/kvm/gaccess.c | 8 ++++---- include/linux/huge_mm.h | 5 +++++ 2 files changed, 9 insertions(+), 4 deletions(-) -- 2.49.0
