| Message ID | 20100504220418.083929bc.takuya.yoshikawa@gmail.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
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@oss.ntt.co.jp> > Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> > CC: Alexander Graf <agraf@suse.de> > CC: Benjamin Herrenschmidt <benh@kernel.crashing.org> > CC: Paul Mackerras <paulus@samba.org> > --- > 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
>> >> +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 :) OK, I'll change like that! I like brackets style too :) > > > Alex >
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); + if (!access_ok(VERIFY_WRITE, p, 1)) + return -EFAULT; + + if (__get_user(val, p)) + return -EFAULT; + + val |= 1U << (nr % BITS_PER_BYTE); + if (__put_user(val, p)) + return -EFAULT; + + return 0; +} + /* more complex routines */