um: make stub data pages size tweakable

There's a lot of code here that hard-codes that the
data is a single page, and right now that seems to
be sufficient, but to make it easier to change this
in the future, add a new STUB_DATA_PAGES constant
and use it throughout the code.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

5 files changed, 18 insertions, 12 deletions

diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
index 9a0bd648d872..9ec3015bc5e2 100644
--- a/arch/um/include/shared/as-layout.h
+++ b/arch/um/include/shared/as-layout.h
@@ -23,7 +23,8 @@
 #define STUB_START stub_start
 #define STUB_CODE STUB_START
 #define STUB_DATA (STUB_CODE + UM_KERN_PAGE_SIZE)
-#define STUB_END (STUB_DATA + UM_KERN_PAGE_SIZE)
+#define STUB_DATA_PAGES 1 /* must be a power of two */
+#define STUB_END (STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE)
 
 #ifndef __ASSEMBLY__
 
diff --git a/arch/um/kernel/skas/clone.c b/arch/um/kernel/skas/clone.c
index ff5061f29167..62435187dda4 100644
--- a/arch/um/kernel/skas/clone.c
+++ b/arch/um/kernel/skas/clone.c
@@ -24,11 +24,12 @@
 void __attribute__ ((__section__ (".__syscall_stub")))
 stub_clone_handler(void)
 {
-	struct stub_data *data = get_stub_page();
+	struct stub_data *data = get_stub_data();
 	long err;
 
 	err = stub_syscall2(__NR_clone, CLONE_PARENT | CLONE_FILES | SIGCHLD,
-			    (unsigned long)data + UM_KERN_PAGE_SIZE / 2);
+			    (unsigned long)data +
+				STUB_DATA_PAGES * UM_KERN_PAGE_SIZE / 2);
 	if (err) {
 		data->parent_err = err;
 		goto done;
diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
index 125df465e8ea..656fe16c9b63 100644
--- a/arch/um/kernel/skas/mmu.c
+++ b/arch/um/kernel/skas/mmu.c
@@ -21,7 +21,7 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
 	unsigned long stack = 0;
 	int ret = -ENOMEM;
 
-	stack = get_zeroed_page(GFP_KERNEL);
+	stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
 	if (stack == 0)
 		goto out;
 
@@ -52,7 +52,7 @@ int init_new_context(struct task_struct *task, struct mm_struct *mm)
 
  out_free:
 	if (to_mm->id.stack != 0)
-		free_page(to_mm->id.stack);
+		free_pages(to_mm->id.stack, ilog2(STUB_DATA_PAGES));
  out:
 	return ret;
 }
@@ -74,6 +74,6 @@ void destroy_context(struct mm_struct *mm)
 	}
 	os_kill_ptraced_process(mmu->id.u.pid, 1);
 
-	free_page(mmu->id.stack);
+	free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
 	free_ldt(mmu);
 }
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
index 8dcda617b8bf..0a23a98d4ca0 100644
--- a/arch/um/kernel/um_arch.c
+++ b/arch/um/kernel/um_arch.c
@@ -326,9 +326,13 @@ int __init linux_main(int argc, char **argv)
 		add_arg(DEFAULT_COMMAND_LINE_CONSOLE);
 
 	host_task_size = os_get_top_address();
-	/* reserve two pages for the stubs */
-	host_task_size -= 2 * PAGE_SIZE;
-	stub_start = host_task_size;
+	/* reserve a few pages for the stubs (taking care of data alignment) */
+	/* align the data portion */
+	BUILD_BUG_ON(!is_power_of_2(STUB_DATA_PAGES));
+	stub_start = (host_task_size - 1) & ~(STUB_DATA_PAGES * PAGE_SIZE - 1);
+	/* another page for the code portion */
+	stub_start -= PAGE_SIZE;
+	host_task_size = stub_start;
 
 	/*
 	 * TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index b1ea53285af1..9464833e741a 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -262,7 +262,7 @@ static int userspace_tramp(void *stack)
 	if (stack != NULL) {
 		fd = phys_mapping(uml_to_phys(stack), &offset);
 		addr = mmap((void *) STUB_DATA,
-			    UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
+			    STUB_DATA_PAGES * UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
 			    MAP_FIXED | MAP_SHARED, fd, offset);
 		if (addr == MAP_FAILED) {
 			printk(UM_KERN_ERR "mapping segfault stack at 0x%lx failed, errno = %d\n",
@@ -277,7 +277,7 @@ static int userspace_tramp(void *stack)
 				  (unsigned long) stub_segv_handler -
 				  (unsigned long) __syscall_stub_start;
 
-		set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
+		set_sigstack((void *) STUB_DATA, STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
 		sigemptyset(&sa.sa_mask);
 		sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
 		sa.sa_sigaction = (void *) v;
@@ -515,7 +515,7 @@ static int __init init_thread_regs(void)
 	thread_regs[REGS_IP_INDEX] = STUB_CODE +
 				(unsigned long) stub_clone_handler -
 				(unsigned long) __syscall_stub_start;
-	thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
+	thread_regs[REGS_SP_INDEX] = STUB_DATA + STUB_DATA_PAGES * UM_KERN_PAGE_SIZE -
 		sizeof(void *);
 #ifdef __SIGNAL_FRAMESIZE
 	thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;