um: Save FPU registers between task switches
Some time ago Jeff prepared 42daba316557 ("uml: stop saving process FP
state") for UML to stop saving the process FP state between task
switches. The assumption was that since with SKAS0 every guest process
runs inside a host process context the host OS will take care of keeping
the proper FP state.
Unfortunately this is not true for multi-threaded applications, where
all guest threads share a single host process context yet all may use
the FPU on their own. Although I haven't verified it I suspect things
to be even worse in SKAS3 mode where all guest processes run inside a
single host process.
The patch reintroduces the saving and restoring of the FP context
between task switches.
[richard@nod.at: Ingo posted this patch in 2009, sadly it was never applied
and got lost. Now in 2011 the problem was reported by Gunnar.]
Signed-off-by: Ingo van Lil <inguin@gmx.de>
Signed-off-by: Richard Weinberger <richard@nod.at>
Reported-by: <gunnarlindroth@hotmail.com>
Tested-by: <gunnarlindroth@hotmail.com>
Cc: Stanislav Meduna <stano@meduna.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index d6e0a22..dee0e8c 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -373,6 +373,9 @@
if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp))
fatal_sigsegv();
+ if (put_fp_registers(pid, regs->fp))
+ fatal_sigsegv();
+
/* Now we set local_using_sysemu to be used for one loop */
local_using_sysemu = get_using_sysemu();
@@ -399,6 +402,12 @@
fatal_sigsegv();
}
+ if (get_fp_registers(pid, regs->fp)) {
+ printk(UM_KERN_ERR "userspace - get_fp_registers failed, "
+ "errno = %d\n", errno);
+ fatal_sigsegv();
+ }
+
UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
if (WIFSTOPPED(status)) {
@@ -457,10 +466,11 @@
}
static unsigned long thread_regs[MAX_REG_NR];
+static unsigned long thread_fp_regs[FP_SIZE];
static int __init init_thread_regs(void)
{
- get_safe_registers(thread_regs);
+ get_safe_registers(thread_regs, thread_fp_regs);
/* Set parent's instruction pointer to start of clone-stub */
thread_regs[REGS_IP_INDEX] = STUB_CODE +
(unsigned long) stub_clone_handler -
@@ -503,6 +513,13 @@
return err;
}
+ err = put_fp_registers(pid, thread_fp_regs);
+ if (err < 0) {
+ printk(UM_KERN_ERR "copy_context_skas0 : put_fp_registers "
+ "failed, pid = %d, err = %d\n", pid, err);
+ return err;
+ }
+
/* set a well known return code for detection of child write failure */
child_data->err = 12345678;