• Ingo van Lil's avatar
    um: Save FPU registers between task switches · fbfe9c84
    Ingo van Lil authored
    Some time ago Jeff prepared 42daba31 ("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: default avatarIngo van Lil <inguin@gmx.de>
    Signed-off-by: default avatarRichard Weinberger <richard@nod.at>
    Reported-by: <gunnarlindroth@hotmail.com>
    Tested-by: <gunnarlindroth@hotmail.com>
    Cc: Stanislav Meduna <stano@meduna.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    fbfe9c84
ptrace.h 7.44 KB