2 files changed, 15 insertions, 23 deletions

diff --git a/arch/um/Kconfig b/arch/um/Kconfig
index ec9711d068b7..41913504a56e 100644
--- a/arch/um/Kconfig
+++ b/arch/um/Kconfig
@@ -142,13 +142,17 @@ config MAGIC_SYSRQ
 
 config KERNEL_STACK_ORDER
         int "Kernel stack size order"
-        default 1 if 64BIT
-        range 1 10 if 64BIT
-        default 0 if !64BIT
+        default 2 if 64BIT
+        range 2 10 if 64BIT
+        default 1 if !64BIT
         help
           This option determines the size of UML kernel stacks.  They will
           be 1 << order pages.  The default is OK unless you're running Valgrind
           on UML, in which case, set this to 3.
+          It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on
+          older (pre-2017) CPUs. It is not recommended on newer CPUs due to the
+          increase in the size of the state which needs to be saved when handling
+          signals.
 
 config MMAPPER
         tristate "iomem emulation driver"
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index bf0acb8aad8b..75b10235d369 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -31,29 +31,23 @@ void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *) = {
 
 static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
 {
-        struct uml_pt_regs *r;
+        struct uml_pt_regs r;
         int save_errno = errno;
 
-        r = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
-        if (!r)
-                panic("out of memory");
-
-        r->is_user = 0;
+        r.is_user = 0;
         if (sig == SIGSEGV) {
                 /* For segfaults, we want the data from the sigcontext. */
-                get_regs_from_mc(r, mc);
-                GET_FAULTINFO_FROM_MC(r->faultinfo, mc);
+                get_regs_from_mc(&r, mc);
+                GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
         }
 
         /* enable signals if sig isn't IRQ signal */
         if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGALRM))
                 unblock_signals();
 
-        (*sig_info[sig])(sig, si, r);
+        (*sig_info[sig])(sig, si, &r);
 
         errno = save_errno;
-
-        free(r);
 }
 
 /*
@@ -91,17 +85,11 @@ void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
 
 static void timer_real_alarm_handler(mcontext_t *mc)
 {
-        struct uml_pt_regs *regs;
-
-        regs = uml_kmalloc(sizeof(struct uml_pt_regs), UM_GFP_ATOMIC);
-        if (!regs)
-                panic("out of memory");
+        struct uml_pt_regs regs;
 
         if (mc != NULL)
-                get_regs_from_mc(regs, mc);
-        timer_handler(SIGALRM, NULL, regs);
-
-        free(regs);
+                get_regs_from_mc(&regs, mc);
+        timer_handler(SIGALRM, NULL, &regs);
 }
 
 void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)