[PATCH v2 13/20] arm64: Support hugetlb vmemmap optimization

[James Houghton <jthoughton@google.com>]

Support HVO if HW AF and BBML3 are supported. These are the required
features for the vmemmap to be modified in place.

On arm64 systems that do not have the required hardware features to
support HVO, the HVO sysctl will not appear, and any attempts to enable
HVO (either via the command line or via
CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y) will have no effect.

Signed-off-by: James Houghton <jthoughton@google.com>
---
 arch/arm64/Kconfig               | 2 ++
 arch/arm64/include/asm/hugetlb.h | 7 +++++++
 mm/hugetlb_vmemmap.c             | 4 ++++
 3 files changed, 13 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b51d23a62c92..e4c87487bc7f 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -92,7 +92,9 @@ 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_VMEMMAP_RO_AFTER_INIT
 	select ARCH_WANT_LD_ORPHAN_WARN
+	select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP if ARM64_HW_AFDBM
 	select ARCH_WANTS_EXECMEM_LATE
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES
diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
index d038ff14d16c..938d7896a31e 100644
--- a/arch/arm64/include/asm/hugetlb.h
+++ b/arch/arm64/include/asm/hugetlb.h
@@ -11,6 +11,7 @@
 #define __ASM_HUGETLB_H
 
 #include <asm/cacheflush.h>
+#include <asm/cpufeature.h>
 #include <asm/mte.h>
 #include <asm/page.h>
 
@@ -65,6 +66,12 @@ extern void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 					 unsigned long addr, pte_t *ptep,
 					 pte_t old_pte, pte_t new_pte);
 
+#define __HAVE_ARCH_HVO_SUPPORTED
+static inline bool arch_hugetlb_vmemmap_optimization_supported(void)
+{
+	return system_supports_bbm_through_af();
+}
+
 #include <asm-generic/hugetlb.h>
 
 static inline void __flush_hugetlb_tlb_range(struct vm_area_struct *vma,
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index c1c736dd08b9..fabf2b25fe59 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -85,6 +85,10 @@ static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start,
 
 		/* Make pte visible before pmd. See comment in pmd_install(). */
 		smp_wmb();
+		/*
+		 * On arm64, this requires BBML3. Its support has already been
+		 * checked.
+		 */
 		pmd_populate_kernel(&init_mm, pmd, pgtable);
 		if (!(walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH))
 			flush_tlb_kernel_range(start, start + PMD_SIZE);
-- 
2.56.0.rc1.315.gc6ed9934b7-goog