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um: Save FPU registers between task switches

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Some time ago Jeff prepared 42daba3165 ("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>
This commit is contained in:
Ingo van Lil
2011-09-14 16:21:23 -07:00
committed by Linus Torvalds
parent b40997b872
commit fbfe9c847e
7 changed files with 31 additions and 5 deletions
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2
arch/um/kernel/process.c
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@@ -202,7 +202,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
arch_copy_thread(&current->thread.arch, &p->thread.arch);
}
else {
get_safe_registers(p->thread.regs.regs.gp);
get_safe_registers(p->thread.regs.regs.gp, p->thread.regs.regs.fp);
p->thread.request.u.thread = current->thread.request.u.thread;
handler = new_thread_handler;
}