[PATCHv2 2/3] arm64: Add support for ARCH_SUPPORTS_DEBUG_PAGEALLOC

[Laura Abbott]

ARCH_SUPPORTS_DEBUG_PAGEALLOC provides a hook to map and unmap
pages for debugging purposes. This requires memory be mapped
with PAGE_SIZE mappings since breaking down larger mappings
at runtime will lead to TLB conflicts. Check if debug_pagealloc
is enabled at runtime and if so, map everyting with PAGE_SIZE
pages. Implement the functions to actually map/unmap the
pages at runtime.


Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
---
 arch/arm64/Kconfig       |  3 +++
 arch/arm64/mm/mmu.c      | 10 +++++++---
 arch/arm64/mm/pageattr.c | 40 +++++++++++++++++++++++++++++++++-------
 3 files changed, 43 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 8cc6228..0f33218 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -537,6 +537,9 @@ config HOTPLUG_CPU
 source kernel/Kconfig.preempt
 source kernel/Kconfig.hz
 
+config ARCH_SUPPORTS_DEBUG_PAGEALLOC
+	def_bool y
+
 config ARCH_HAS_HOLES_MEMORYMODEL
 	def_bool y if SPARSEMEM
 
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 103ebc0..5abbd30 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -181,7 +181,8 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
 	do {
 		next = pmd_addr_end(addr, end);
 		/* try section mapping first */
-		if (((addr | next | phys) & ~SECTION_MASK) == 0) {
+		if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
+		      (!debug_pagealloc_enabled() || !pgtable_alloc)) {
 			pmd_t old_pmd =*pmd;
 			set_pmd(pmd, __pmd(phys |
 					   pgprot_val(mk_sect_prot(prot))));
@@ -208,8 +209,11 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
 }
 
 static inline bool use_1G_block(unsigned long addr, unsigned long next,
-			unsigned long phys)
+			unsigned long phys, phys_addr_t (*pgtable_alloc)(void))
 {
+	if (pgtable_alloc && debug_pagealloc_enabled())
+		return false;
+
 	if (PAGE_SHIFT != 12)
 		return false;
 
@@ -241,7 +245,7 @@ static void alloc_init_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
 		/*
 		 * For 4K granule only, attempt to put down a 1GB block
 		 */
-		if (use_1G_block(addr, next, phys)) {
+		if (use_1G_block(addr, next, phys, pgtable_alloc)) {
 			pud_t old_pud = *pud;
 			set_pud(pud, __pud(phys |
 					   pgprot_val(mk_sect_prot(prot))));
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 1360a02..69a8a7d 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -38,7 +38,8 @@ static int change_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
 }
 
 static int change_memory_common(unsigned long addr, int numpages,
-				pgprot_t set_mask, pgprot_t clear_mask)
+				pgprot_t set_mask, pgprot_t clear_mask,
+				bool ignore_vma_check)
 {
 	unsigned long start = addr;
 	unsigned long size = PAGE_SIZE*numpages;
@@ -65,11 +66,14 @@ static int change_memory_common(unsigned long addr, int numpages,
 	 *
 	 * So check whether the [addr, addr + size) interval is entirely
 	 * covered by precisely one VM area that has the VM_ALLOC flag set.
+	 *
+	 * The one exception to this is is we're forcing everything to be
+	 * page mapped with DEBUG_PAGEALLOC
 	 */
 	area = find_vm_area((void *)addr);
-	if (!area ||
+	if (!ignore_vma_check && (!area ||
 	    end > (unsigned long)area->addr + area->size ||
-	    !(area->flags & VM_ALLOC))
+	    !(area->flags & VM_ALLOC)))
 		return -EINVAL;
 
 	data.set_mask = set_mask;
@@ -86,21 +90,24 @@ int set_memory_ro(unsigned long addr, int numpages)
 {
 	return change_memory_common(addr, numpages,
 					__pgprot(PTE_RDONLY),
-					__pgprot(PTE_WRITE));
+					__pgprot(PTE_WRITE),
+					false);
 }
 
 int set_memory_rw(unsigned long addr, int numpages)
 {
 	return change_memory_common(addr, numpages,
 					__pgprot(PTE_WRITE),
-					__pgprot(PTE_RDONLY));
+					__pgprot(PTE_RDONLY),
+					false);
 }
 
 int set_memory_nx(unsigned long addr, int numpages)
 {
 	return change_memory_common(addr, numpages,
 					__pgprot(PTE_PXN),
-					__pgprot(0));
+					__pgprot(0),
+					false);
 }
 EXPORT_SYMBOL_GPL(set_memory_nx);
 
@@ -108,6 +115,25 @@ int set_memory_x(unsigned long addr, int numpages)
 {
 	return change_memory_common(addr, numpages,
 					__pgprot(0),
-					__pgprot(PTE_PXN));
+					__pgprot(PTE_PXN),
+					false);
 }
 EXPORT_SYMBOL_GPL(set_memory_x);
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+void __kernel_map_pages(struct page *page, int numpages, int enable)
+{
+	unsigned long addr = (unsigned long) page_address(page);
+
+	if (enable)
+		change_memory_common(addr, numpages,
+					__pgprot(PTE_VALID),
+					__pgprot(0),
+					true);
+	else
+		change_memory_common(addr, numpages,
+					__pgprot(0),
+					__pgprot(PTE_VALID),
+					true);
+}
+#endif
-- 
2.5.0