On lunedì 17 ottobre 2022 11:37:18 CEST Zhao Liu wrote: > From: Zhao Liu <zhao1.liu@xxxxxxxxx> > > The use of kmap_atomic() is being deprecated in favor of > kmap_local_page()[1]. > > The main difference between atomic and local mappings is that local > mappings doesn't disable page faults or preemption. > > In drm/i915/gem/i915_gem_phys.c, the functions > i915_gem_object_get_pages_phys() and i915_gem_object_put_pages_phys() > don't need to disable pagefaults and preemption for mapping because of > these 2 reasons: > > 1. The flush operation is safe for CPU hotplug when preemption is not > disabled. In drm/i915/gem/i915_gem_object.c, the functions > i915_gem_object_get_pages_phys() and i915_gem_object_put_pages_phys() > calls drm_clflush_virt_range() to use CLFLUSHOPT or WBINVD to flush. > Since CLFLUSHOPT is global on x86 and WBINVD is called on each cpu in > drm_clflush_virt_range(), the flush operation is global and any issue > with cpu's being added or removed can be handled safely. > > 2. Any context switch caused by preemption or sleep (pagefault may > cause sleep) doesn't affect the validity of local mapping. > > Therefore, i915_gem_object_get_pages_phys() and > i915_gem_object_put_pages_phys() are two functions where the use of > kmap_local_page() in place of kmap_atomic() is correctly suited. > > Convert the calls of kmap_atomic() / kunmap_atomic() to > kmap_local_page() / kunmap_local(). > I have here the same questions as in 1/9. > [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@xxxxxxxxx > > Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx> > Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Suggested-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> > Signed-off-by: Zhao Liu <zhao1.liu@xxxxxxxxx> > --- > Suggested by credits: > Dave: Referred to his explanation about cache flush. > Ira: Referred to his task document, review comments and explanation about > cache flush. > Fabio: Referred to his boiler plate commit message. > --- > drivers/gpu/drm/i915/gem/i915_gem_phys.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > b/drivers/gpu/drm/i915/gem/i915_gem_phys.c index 0d0e46dae559..d602ba19ecb2 100644 > --- a/drivers/gpu/drm/i915/gem/i915_gem_phys.c > +++ b/drivers/gpu/drm/i915/gem/i915_gem_phys.c > @@ -66,10 +66,10 @@ static int i915_gem_object_get_pages_phys(struct drm_i915_gem_object > *obj) if (IS_ERR(page)) > goto err_st; > > - src = kmap_atomic(page); > + src = kmap_local_page(page); > memcpy(dst, src, PAGE_SIZE); > drm_clflush_virt_range(dst, PAGE_SIZE); > - kunmap_atomic(src); > + kunmap_local(src); Please use memcpy_from_page() instead of open coding mapping + memcpy() + unmapping. > > put_page(page); > dst += PAGE_SIZE; > @@ -114,10 +114,10 @@ i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj, > if (IS_ERR(page)) > continue; > > - dst = kmap_atomic(page); > + dst = kmap_local_page(page); > drm_clflush_virt_range(src, PAGE_SIZE); > memcpy(dst, src, PAGE_SIZE); > - kunmap_atomic(dst); > + kunmap_local(dst); For the same reasons said above, memcpy_to_page() should be used here and avoid open coding of three functions. Using those helpers forces you to move drm_clflush_virt_range() out of the mapping / un-mapping region. I may be wrong, however I'm pretty sure that the relative positions of each of those call sites is something that cannot be randomly chosen. Thanks, Fabio > > set_page_dirty(page); > if (obj->mm.madv == I915_MADV_WILLNEED)
