(5/14/12 2:52 AM), Inki Dae wrote: > > >> -----Original Message----- >> From: KOSAKI Motohiro [mailto:kosaki.motohiro at gmail.com] >> Sent: Monday, May 14, 2012 3:33 PM >> To: Inki Dae >> Cc: airlied at linux.ie; dri-devel at lists.freedesktop.org; j.glisse at >> gmail.com; >> minchan at kernel.org; kyungmin.park at samsung.com; sw0312.kim at >> samsung.com; >> jy0922.shim at samsung.com >> Subject: Re: [PATCH 2/2 v4] drm/exynos: added userptr feature. >> >>> + npages = buf->size>> PAGE_SHIFT; >> >> Why round down? usually we use round up. >> > > The size was already rounded up by exynos_drm_gem_userptr_ioctl so this is > just used to get page count.
got it. >>> + down_read(¤t->mm->mmap_sem); >>> + >>> + /* >>> + * Basically, all the pages from get_user_pages() can not be not >> only >>> + * migrated by CMA but also swapped out. >>> + * >>> + * The migration issue. >>> + * - Pages reserved by CMA for some device using DMA could be >> used by >>> + * kernel and if the device driver wants to use those pages >>> + * while being used by kernel then the pages are copied into >>> + * other ones allocated to migrate them and then finally, >>> + * the device driver can use the pages for itself. >>> + * Thus, migrated, the pages being accessed by DMA could be >> changed >>> + * to other so this situation may incur that DMA accesses any >> pages >>> + * it doesn't want. >>> + * >>> + * But the use of get_user_pages is safe from such magration >> issue >>> + * because all the pages from get_user_pages CAN NOT be not only >>> + * migrated, but also swapped out. >>> + */ >>> + get_npages = get_user_pages(current, current->mm, userptr, >>> + npages, write, 1, buf->pages, > NULL); >> >> Why force=1? It is almostly core-dump specific option. Why don't you >> return > > I know that force indicates whether to force write access even if user > mapping is readonly. right. and then, usually we don't want to ignore access permission. but note, I'm only talk about generic thing. I have no knowledge drm area. > so we just want to use pages from get_user_pages as > read/write permission. >> EFAULT when the page has write permission. IOW, Why your Xorg module >> don't map memory w/ PROT_WRITE? > > No, Xorg can map memory w/ PROT_WRITE. Couldn't the Xorg map w/ PROT_WRITE > if force = 1? plz, let me know if there is my missing point. I meant, if Xorg always use PROT_WRITE, you don't need force=1.
