Takuya Yoshikawa wrote: > During the work of KVM's dirty page logging optimization, we encountered > the need of manipulating bitmaps in user space efficiantly. To achive this, > we introduce a uaccess function for setting a bit in user space following > Avi's suggestion. > > KVM is now using dirty bitmaps for live-migration and VGA. Although we need > to update them from kernel side, copying them every time for updating the > dirty log is a big bottleneck. Especially, we tested that zero-copy bitmap > manipulation improves responses of GUI manipulations a lot. > > We also found one similar need in drivers/vhost/vhost.c in which the author > implemented set_bit_to_user() locally using inefficient functions: see TODO > at the top of that. > > Probably, this kind of need would be common for virtualization area. > > So we introduce a function set_bit_user_non_atomic(). > > Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx> > Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx> > CC: Alexander Graf <agraf@xxxxxxx> > CC: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> > CC: Paul Mackerras <paulus@xxxxxxxxx> > --- > arch/powerpc/include/asm/uaccess.h | 19 +++++++++++++++++++ > 1 files changed, 19 insertions(+), 0 deletions(-) > > diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h > index 3a01ce8..f878326 100644 > --- a/arch/powerpc/include/asm/uaccess.h > +++ b/arch/powerpc/include/asm/uaccess.h > @@ -321,6 +321,25 @@ do { \ > __gu_err; \ > }) > > +static inline int set_bit_user_non_atomic(int nr, void __user *addr) > +{ > + u8 __user *p; > + u8 val; > + > + p = (u8 __user *)((unsigned long)addr + nr / BITS_PER_BYTE); > Does C do the + or the / first? Either way, I'd like to see brackets here :) Alex -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html