[RFC][PATCH 3/4] arm64: Add support for ARCH_SUPPORTS_DEBUG_PAGEALLOC

[Laura Abbott]

With support for forcing all memory, we can now easily map and unmap
individual pages for debugging purposes. Add support for
ARCH_SUPPORTS_DEBUG_PAGEALLOC to map and unmap pages when this
debugging feature is enabled.

Signed-off-by: Laura Abbott <labb...@fedoraproject.org>
---
 arch/arm64/Kconfig       |  3 +++
 arch/arm64/mm/pageattr.c | 40 +++++++++++++++++++++++++++++++++-------
 2 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index faf7eac..0d757eb 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -518,6 +518,9 @@ config FORCE_PAGES
 source kernel/Kconfig.preempt
 source kernel/Kconfig.hz
 
+config ARCH_SUPPORTS_DEBUG_PAGEALLOC
+       def_bool y if FORCE_PAGES
+
 config ARCH_HAS_HOLES_MEMORYMODEL
        def_bool y if SPARSEMEM
 
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 1360a02..16efc7c 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
         */
        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_ARCH_SUPPORTS_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