[PATCH] arm64: mm: hugetlb: Disable HUGETLB_PAGE_OPTIMIZE_VMEMMAP

[Catalin Marinas]

Revert the HUGETLB_PAGE_FREE_VMEMMAP selection from commit 1e63ac088f20
("arm64: mm: hugetlb: enable HUGETLB_PAGE_FREE_VMEMMAP for arm64") but
keep the flush_dcache_page() compound_head() change as it aligns with
the corresponding check in the __sync_icache_dcache() function.

The original config option was renamed in commit 47010c040dec ("mm:
hugetlb_vmemmap: cleanup CONFIG_HUGETLB_PAGE_FREE_VMEMMAP*") to
HUGETLB_PAGE_OPTIMIZE_VMEMMAP and the flush_dcache_page() check was
further simplified by commit 2da1c30929a2 ("mm: hugetlb_vmemmap: delete
hugetlb_optimize_vmemmap_enabled()").

The reason for the revert is that the generic vmemmap_remap_pte()
function changes both the permissions (writeable to read-only) and the
output address (pfn) of the vmemmap ptes. This is deemed UNPREDICTABLE
by the Arm architecture without a break-before-make sequence (make the
PTE invalid, TLBI, write the new valid PTE). However, such sequence is
not possible since the vmemmap may be concurrently accessed by the
kernel. Disable the optimisation until a better solution is found.

Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Fixes: 1e63ac088f20 ("arm64: mm: hugetlb: enable HUGETLB_PAGE_FREE_VMEMMAP for arm64")
Cc: <stable at vger.kernel.org> # 5.19.x
Cc: Muchun Song <muchun.song at linux.dev>
Cc: Will Deacon <will at kernel.org>
Cc: Anshuman Khandual <anshuman.khandual at arm.com>
Link: https://lore.kernel.org/r/Y9pZALdn3pKiJUeQ@arm.com
---
 arch/arm64/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 619ab046744a..71c35178e017 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -100,7 +100,6 @@ config ARM64
 	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
-	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES

base-commit: b61b82f81e095fe265b0614045d17b08e6ee5c72