On Wed, 28 Sep 2011 11:57:24 +0200, Daniel Vetter <daniel.vet...@ffwll.ch> wrote: > The helper functions used are designed for pagecache io and splice, > i.e. they prefault at most PAGE_SIZE bytes spanning at most 2 pages. > > pread/pwrite want to write/read much more to avoid dropping the > struct_mutex lock in between. So write our helper function to prefault. > We're the only user of these pagemap.h helpers that want this behaviour, > so keep these new helpers private. > > Based on a patch by Chris Wilson. In addition to his approach this > alos tries to prefault the last page in case the user address range > crosses a page boundary at the end (and hence might sit on n+1 pages > for at most n*PAGE_SIZE of date). > > As a nice side-effect this rather reliably papers over the current > code's inability to handle non-struct page-backed user memory in the > slow paths. Because the real fix is grossly invasive, I think this > patch is the right thing for backporting. > > Cc: sta...@kernel.org > Cc: Chris Wilson <ch...@chris-wilson.co.uk> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38115 > Signed-off-by: Daniel Vetter <daniel.vet...@ffwll.ch> > --- > drivers/gpu/drm/i915/i915_gem.c | 59 ++++++++++++++++++++++++++++++++++++-- > 1 files changed, 55 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index 5f0f46e..42dc922 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -503,6 +503,32 @@ out: > return ret; > } > > +static inline int __prefault_writeable(char __user *uaddr, int size) > +{ > + int ret; > + char __user *end = uaddr + size - 1; > + > + if (unlikely(size == 0)) > + return 0; > + > + /* > + * Writing zeroes into userspace here is OK, because we know that if > + * the zero gets there, we'll be overwriting it. > + */ > + while (uaddr <= end) { > + ret = __put_user(0, uaddr); > + if (ret != 0) > + return ret; > + uaddr += PAGE_SIZE; > + } > + if (ret == 0) { > + if (((unsigned long)uaddr & PAGE_MASK) != > + ((unsigned long)end & PAGE_MASK)) This is a little ugly. Perhaps,
#define page_align(addr) ((unsigned long)addr & PAGE_MASK) if (page_align(uaddr) != page_align(end)) Otherwise, both are Reviewed-by: Chris Wilson <ch...@chris-wilson.co.uk> -Chris -- Chris Wilson, Intel Open Source Technology Centre _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
