• Paul Mackerras's avatar
    powerpc: Fix system calls on Cell entered with XER.SO=1 · ab598b66
    Paul Mackerras authored
    It turns out that on Cell, on a kernel with CONFIG_VIRT_CPU_ACCOUNTING
    = y, if a program sets the SO (summary overflow) bit in the XER and
    then does a system call, the SO bit in CR0 will be set on return
    regardless of whether the system call detected an error.  Since CR0.SO
    is used as the error indication from the system call, this means that
    all system calls appear to fail.
    
    The reason is that the workaround for the timebase bug on Cell uses a
    compare instruction.  With CONFIG_VIRT_CPU_ACCOUNTING = y, the
    ACCOUNT_CPU_USER_ENTRY macro reads the timebase, so we end up doing a
    compare instruction, which copies XER.SO to CR0.SO.  Since we were
    doing this in the system call entry patch after clearing CR0.SO but
    before saving the CR, this meant that the saved CR image had CR0.SO
    set if XER.SO was set on entry.
    
    This fixes it by moving the clearing of CR0.SO to after the
    ACCOUNT_CPU_USER_ENTRY call in the system call entry path.
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
    Acked-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    ab598b66
entry_64.S 21.8 KB