Le 31/08/2023 à 16:41, Thomas Zimmermann a écrit : > Hi, > > there's a per-architecture function called fb_pgprotect() that sets > VMA's vm_page_prot for mmaped framebuffers. Most architectures use a > simple implementation based on pgprot_writecomine() [1] or > pgprot_noncached(). [2] > > On PPC this function uses phys_mem_access_prot() and therefore requires > the mmap call's file struct. [3] Removing the file argument would help > with simplifying the caller of fb_pgprotect(). [4] > > Why is the file even required on PPC? > > Is it possible to replace phys_mem_access_prot() with something simpler > that does not use the file struct? Looks like phys_mem_access_prot() defaults to calling pgprot_noncached() see https://elixir.bootlin.com/linux/v6.5/source/arch/powerpc/mm/mem.c#L37 but for a few platforms that's superseeded by pci_phys_mem_access_prot(), see https://elixir.bootlin.com/linux/v6.5/source/arch/powerpc/kernel/pci-common.c#L524 However, as far as I can see pci_phys_mem_access_prot() doesn't use file so you could likely drop that argument on phys_mem_access_prot() on powerpc. But when I for instance look at arm, I see that the file argument is used, see https://elixir.bootlin.com/linux/v6.5/source/arch/arm/mm/mmu.c#L713 So, the simplest is maybe the following, allthough that's probably worth a comment: diff --git a/arch/powerpc/include/asm/fb.h b/arch/powerpc/include/asm/fb.h index 5f1a2e5f7654..8b9b856f476e 100644 --- a/arch/powerpc/include/asm/fb.h +++ b/arch/powerpc/include/asm/fb.h @@ -6,10 +6,9 @@ #include <asm/page.h> -static inline void fb_pgprotect(struct file *file, struct vm_area_struct *vma, - unsigned long off) +static inline void fb_pgprotect(struct vm_area_struct *vma, unsigned long off) { - vma->vm_page_prot = phys_mem_access_prot(file, off >> PAGE_SHIFT, + vma->vm_page_prot = phys_mem_access_prot(NULL, off >> PAGE_SHIFT, vma->vm_end - vma->vm_start, vma->vm_page_prot); } Christophe > > Best regards > Thomas > > > [1] > https://elixir.bootlin.com/linux/v6.5/source/include/asm-generic/fb.h#L19 > [2] > https://elixir.bootlin.com/linux/v6.5/source/arch/mips/include/asm/fb.h#L11 > [3] > https://elixir.bootlin.com/linux/v6.5/source/arch/powerpc/include/asm/fb.h#L12 > [4] > https://elixir.bootlin.com/linux/v6.5/source/drivers/video/fbdev/core/fbmem.c#L1299 > >
