[PATCH V4 3/3] arm64/mm: Enable vmem_altmap support for vmemmap mappings

Anshuman Khandual anshuman.khandual at arm.com
Sun Jul 5 22:56:18 EDT 2020


Device memory ranges when getting hot added into ZONE_DEVICE, might require
their vmemmap mapping's backing memory to be allocated from their own range
instead of consuming system memory. This prevents large system memory usage
for potentially large device memory ranges. Device driver communicates this
request via vmem_altmap structure. Architecture needs to take this request
into account while creating and tearing down vemmmap mappings.

This enables vmem_altmap support in vmemmap_populate() and vmemmap_free()
which includes vmemmap_populate_basepages() used for ARM64_16K_PAGES and
ARM64_64K_PAGES configs.

Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Steve Capper <steve.capper at arm.com>
Cc: David Hildenbrand <david at redhat.com>
Cc: Yu Zhao <yuzhao at google.com>
Cc: Hsin-Yi Wang <hsinyi at chromium.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Tested-by: Jia He <justin.he at arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 arch/arm64/mm/mmu.c | 58 +++++++++++++++++++++++++++++----------------
 1 file changed, 38 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 9c08d1882106..51a1b0e886ff 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -760,15 +760,20 @@ int kern_addr_valid(unsigned long addr)
 }
 
 #ifdef CONFIG_MEMORY_HOTPLUG
-static void free_hotplug_page_range(struct page *page, size_t size)
+static void free_hotplug_page_range(struct page *page, size_t size,
+				    struct vmem_altmap *altmap)
 {
-	WARN_ON(PageReserved(page));
-	free_pages((unsigned long)page_address(page), get_order(size));
+	if (altmap) {
+		vmem_altmap_free(altmap, size >> PAGE_SHIFT);
+	} else {
+		WARN_ON(PageReserved(page));
+		free_pages((unsigned long)page_address(page), get_order(size));
+	}
 }
 
 static void free_hotplug_pgtable_page(struct page *page)
 {
-	free_hotplug_page_range(page, PAGE_SIZE);
+	free_hotplug_page_range(page, PAGE_SIZE, NULL);
 }
 
 static bool pgtable_range_aligned(unsigned long start, unsigned long end,
@@ -791,7 +796,8 @@ static bool pgtable_range_aligned(unsigned long start, unsigned long end,
 }
 
 static void unmap_hotplug_pte_range(pmd_t *pmdp, unsigned long addr,
-				    unsigned long end, bool free_mapped)
+				    unsigned long end, bool free_mapped,
+				    struct vmem_altmap *altmap)
 {
 	pte_t *ptep, pte;
 
@@ -805,12 +811,14 @@ static void unmap_hotplug_pte_range(pmd_t *pmdp, unsigned long addr,
 		pte_clear(&init_mm, addr, ptep);
 		flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 		if (free_mapped)
-			free_hotplug_page_range(pte_page(pte), PAGE_SIZE);
+			free_hotplug_page_range(pte_page(pte),
+						PAGE_SIZE, altmap);
 	} while (addr += PAGE_SIZE, addr < end);
 }
 
 static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr,
-				    unsigned long end, bool free_mapped)
+				    unsigned long end, bool free_mapped,
+				    struct vmem_altmap *altmap)
 {
 	unsigned long next;
 	pmd_t *pmdp, pmd;
@@ -833,16 +841,17 @@ static void unmap_hotplug_pmd_range(pud_t *pudp, unsigned long addr,
 			flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 			if (free_mapped)
 				free_hotplug_page_range(pmd_page(pmd),
-							PMD_SIZE);
+							PMD_SIZE, altmap);
 			continue;
 		}
 		WARN_ON(!pmd_table(pmd));
-		unmap_hotplug_pte_range(pmdp, addr, next, free_mapped);
+		unmap_hotplug_pte_range(pmdp, addr, next, free_mapped, altmap);
 	} while (addr = next, addr < end);
 }
 
 static void unmap_hotplug_pud_range(p4d_t *p4dp, unsigned long addr,
-				    unsigned long end, bool free_mapped)
+				    unsigned long end, bool free_mapped,
+				    struct vmem_altmap *altmap)
 {
 	unsigned long next;
 	pud_t *pudp, pud;
@@ -865,16 +874,17 @@ static void unmap_hotplug_pud_range(p4d_t *p4dp, unsigned long addr,
 			flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
 			if (free_mapped)
 				free_hotplug_page_range(pud_page(pud),
-							PUD_SIZE);
+							PUD_SIZE, altmap);
 			continue;
 		}
 		WARN_ON(!pud_table(pud));
-		unmap_hotplug_pmd_range(pudp, addr, next, free_mapped);
+		unmap_hotplug_pmd_range(pudp, addr, next, free_mapped, altmap);
 	} while (addr = next, addr < end);
 }
 
 static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr,
-				    unsigned long end, bool free_mapped)
+				    unsigned long end, bool free_mapped,
+				    struct vmem_altmap *altmap)
 {
 	unsigned long next;
 	p4d_t *p4dp, p4d;
@@ -887,16 +897,24 @@ static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr,
 			continue;
 
 		WARN_ON(!p4d_present(p4d));
-		unmap_hotplug_pud_range(p4dp, addr, next, free_mapped);
+		unmap_hotplug_pud_range(p4dp, addr, next, free_mapped, altmap);
 	} while (addr = next, addr < end);
 }
 
 static void unmap_hotplug_range(unsigned long addr, unsigned long end,
-				bool free_mapped)
+				bool free_mapped, struct vmem_altmap *altmap)
 {
 	unsigned long next;
 	pgd_t *pgdp, pgd;
 
+	/*
+	 * altmap can only be used as vmemmap mapping backing memory.
+	 * In case the backing memory itself is not being freed, then
+	 * altmap is irrelevant. Warn about this inconsistency when
+	 * encountered.
+	 */
+	WARN_ON(!free_mapped && altmap);
+
 	do {
 		next = pgd_addr_end(addr, end);
 		pgdp = pgd_offset_k(addr);
@@ -905,7 +923,7 @@ static void unmap_hotplug_range(unsigned long addr, unsigned long end,
 			continue;
 
 		WARN_ON(!pgd_present(pgd));
-		unmap_hotplug_p4d_range(pgdp, addr, next, free_mapped);
+		unmap_hotplug_p4d_range(pgdp, addr, next, free_mapped, altmap);
 	} while (addr = next, addr < end);
 }
 
@@ -1069,7 +1087,7 @@ static void free_empty_tables(unsigned long addr, unsigned long end,
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 		struct vmem_altmap *altmap)
 {
-	return vmemmap_populate_basepages(start, end, node, NULL);
+	return vmemmap_populate_basepages(start, end, node, altmap);
 }
 #else	/* !ARM64_SWAPPER_USES_SECTION_MAPS */
 int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
@@ -1101,7 +1119,7 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 		if (pmd_none(READ_ONCE(*pmdp))) {
 			void *p = NULL;
 
-			p = vmemmap_alloc_block_buf(PMD_SIZE, node, NULL);
+			p = vmemmap_alloc_block_buf(PMD_SIZE, node, altmap);
 			if (!p)
 				return -ENOMEM;
 
@@ -1119,7 +1137,7 @@ void vmemmap_free(unsigned long start, unsigned long end,
 #ifdef CONFIG_MEMORY_HOTPLUG
 	WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END));
 
-	unmap_hotplug_range(start, end, true);
+	unmap_hotplug_range(start, end, true, altmap);
 	free_empty_tables(start, end, VMEMMAP_START, VMEMMAP_END);
 #endif
 }
@@ -1410,7 +1428,7 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
 	WARN_ON(pgdir != init_mm.pgd);
 	WARN_ON((start < PAGE_OFFSET) || (end > PAGE_END));
 
-	unmap_hotplug_range(start, end, false);
+	unmap_hotplug_range(start, end, false, NULL);
 	free_empty_tables(start, end, PAGE_OFFSET, PAGE_END);
 }
 
-- 
2.20.1




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