arm64: Add support for ARCH_SUPPORTS_DEBUG_PAGEALLOC

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.

Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
[catalin.marinas@arm.com: static annotation block_mappings_allowed() and #ifdef]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

3 files changed, 63 insertions, 12 deletions

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 53e48a617fef..5a1f2e47d153 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 ef0d66cf5535..a6f28e5b9585 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -149,6 +149,26 @@ static void split_pud(pud_t *old_pud, pmd_t *pmd)
         } while (pmd++, i++, i < PTRS_PER_PMD);
 }
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
+static bool block_mappings_allowed(phys_addr_t (*pgtable_alloc)(void))
+{
+
+        /*
+         * If debug_page_alloc is enabled we must map the linear map
+         * using pages. However, other mappings created by
+         * create_mapping_noalloc must use sections in some cases. Allow
+         * sections to be used in those cases, where no pgtable_alloc
+         * function is provided.
+         */
+        return !pgtable_alloc || !debug_pagealloc_enabled();
+}
+#else
+static bool block_mappings_allowed(phys_addr_t (*pgtable_alloc)(void))
+{
+        return true;
+}
+#endif
+
 static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
                                   phys_addr_t phys, pgprot_t prot,
                                   phys_addr_t (*pgtable_alloc)(void))
@@ -181,7 +201,8 @@ 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 &&
+                      block_mappings_allowed(pgtable_alloc)) {
                         pmd_t old_pmd =*pmd;
                         set_pmd(pmd, __pmd(phys |
                                            pgprot_val(mk_sect_prot(prot))));
@@ -241,7 +262,8 @@ 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) &&
+                    block_mappings_allowed(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 0795c3a36d8f..ca6d268e3313 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -37,14 +37,31 @@ static int change_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
         return 0;
 }
 
+/*
+ * This function assumes that the range is mapped with PAGE_SIZE pages.
+ */
+static int __change_memory_common(unsigned long start, unsigned long size,
+                                pgprot_t set_mask, pgprot_t clear_mask)
+{
+        struct page_change_data data;
+        int ret;
+
+        data.set_mask = set_mask;
+        data.clear_mask = clear_mask;
+
+        ret = apply_to_page_range(&init_mm, start, size, change_page_range,
+                                        &data);
+
+        flush_tlb_kernel_range(start, start + size);
+        return ret;
+}
+
 static int change_memory_common(unsigned long addr, int numpages,
                                 pgprot_t set_mask, pgprot_t clear_mask)
 {
         unsigned long start = addr;
         unsigned long size = PAGE_SIZE*numpages;
         unsigned long end = start + size;
-        int ret;
-        struct page_change_data data;
         struct vm_struct *area;
 
         if (!PAGE_ALIGNED(addr)) {
@@ -75,14 +92,7 @@ static int change_memory_common(unsigned long addr, int numpages,
         if (!numpages)
                 return 0;
 
-        data.set_mask = set_mask;
-        data.clear_mask = clear_mask;
-
-        ret = apply_to_page_range(&init_mm, start, size, change_page_range,
-                                        &data);
-
-        flush_tlb_kernel_range(start, end);
-        return ret;
+        return __change_memory_common(start, size, set_mask, clear_mask);
 }
 
 int set_memory_ro(unsigned long addr, int numpages)
@@ -114,3 +124,19 @@ int set_memory_x(unsigned long addr, int numpages)
                                         __pgprot(PTE_PXN));
 }
 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, PAGE_SIZE * numpages,
+                                        __pgprot(PTE_VALID),
+                                        __pgprot(0));
+        else
+                __change_memory_common(addr, PAGE_SIZE * numpages,
+                                        __pgprot(0),
+                                        __pgprot(PTE_VALID));
+}
+#endif