From: Ingo van Lil Date: Wed, 14 Sep 2011 23:21:23 +0000 (-0700) Subject: um: Save FPU registers between task switches X-Git-Tag: v3.1-rc7~56 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fbfe9c847edf57ac8232aeafb290f272289893a3;p=pandora-kernel.git 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 Signed-off-by: Richard Weinberger Reported-by: Tested-by: Cc: Stanislav Meduna Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Reading git-diff-tree failed