[SRU][B][PATCH 0/1] revert v4.17 stable backport patch

[Krzysztof Kozlowski]

BugLink: https://bugs.launchpad.net/bugs/1946464

[Impact]

Commit 5047ef5725ed ("x86/mm: Don't free P4D table when it is folded at runtime") should not be backported to v4.15 because:
1. It adds pgtable_l5_enabled which does not exist in v4.15,
2. It is marked as v4.17+
3. It is marked as fixing commit which does not exist in v4.15 and was not backported there.

allyesconfig in x86_64 fails to build:
---
In file included from ../arch/x86/include/asm/mmu_context.h:12,
                 from ../include/linux/mmu_context.h:5,
                 from ../arch/x86/kvm/../../../virt/kvm/async_pf.c:26:
../arch/x86/include/asm/pgalloc.h: In function ‘p4d_free’:
../arch/x86/include/asm/pgalloc.h:185:7: error: ‘pgtable_l5_enabled’ undeclared (first use in this function); did you mean ‘movable_node_enabled’?
  185 | if (!pgtable_l5_enabled)
      | ^~~~~~~~~~~~~~~~~~
      | movable_node_enabled

---

[Test Plan]

Compile the x86_64 KVM code.

[Where problems could occur]

If backport commit is actually needed, e.g. when we backport 5-level page tables and commit 98219dda2ab5 ("x86/mm: Fold p4d page table layer at runtime"), this could cause double-free and memory corruption.

When backporting x86_64 5-level pages, we need to bring this commit as well.

Best regards,
Krzysztof

Krzysztof Kozlowski (1):
  UBUNTU: SAUCE: Revert "x86/mm: Don't free P4D table when it is folded
    at runtime"

 arch/x86/include/asm/pgalloc.h | 3 ---
 1 file changed, 3 deletions(-)

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2.30.2