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/mem.c b/arch/um/os-Linux/skas/mem.c
index d261f17..e771398 100644
--- a/arch/um/os-Linux/skas/mem.c
+++ b/arch/um/os-Linux/skas/mem.c
@@ -39,7 +39,7 @@
static int __init init_syscall_regs(void)
{
- get_safe_registers(syscall_regs);
+ get_safe_registers(syscall_regs, NULL);
syscall_regs[REGS_IP_INDEX] = STUB_CODE +
((unsigned long) &batch_syscall_stub -
(unsigned long) &__syscall_stub_start);