Re: [PATCH 4/6] vhost_vdpa: support doorbell mapping via mmap

From: Jason Wang
Date: Tue Jun 02 2020 - 02:49:59 EST

On 2020/6/2 äå12:56, Michael S. Tsirkin wrote:
On Tue, Jun 02, 2020 at 03:22:49AM +0800, kbuild test robot wrote:
Hi Jason,

I love your patch! Yet something to improve:

[auto build test ERROR on vhost/linux-next]
[also build test ERROR on linus/master v5.7 next-20200529]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see]

base: linux-next
config: m68k-randconfig-r011-20200601 (attached as .config)
compiler: m68k-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
wget -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=m68k

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot<lkp@xxxxxxxxx>

All errors (new ones prefixed by >>, old ones prefixed by <<):

drivers/vhost/vdpa.c: In function 'vhost_vdpa_fault':
drivers/vhost/vdpa.c:754:22: error: implicit declaration of function 'pgprot_noncached' [-Werror=implicit-function-declaration]
754 | vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
| ^~~~~~~~~~~~~~~~
drivers/vhost/vdpa.c:754:22: error: incompatible types when assigning to type 'pgprot_t' {aka 'struct <anonymous>'} from type 'int'
cc1: some warnings being treated as errors

vim +/pgprot_noncached +754 drivers/vhost/vdpa.c

743 static vm_fault_t vhost_vdpa_fault(struct vm_fault *vmf)
744 {
745 struct vhost_vdpa *v = vmf->vma->vm_file->private_data;
746 struct vdpa_device *vdpa = v->vdpa;
747 const struct vdpa_config_ops *ops = vdpa->config;
748 struct vdpa_notification_area notify;
749 struct vm_area_struct *vma = vmf->vma;
750 u16 index = vma->vm_pgoff;
752 notify = ops->get_vq_notification(vdpa, index);
> 754 vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
755 if (remap_pfn_range(vma, vmf->address & PAGE_MASK,
756 notify.addr >> PAGE_SHIFT, PAGE_SIZE,
757 vma->vm_page_prot))
758 return VM_FAULT_SIGBUS;
760 return VM_FAULT_NOPAGE;
761 }
Yes well, all this remapping clearly has no chance to work
on systems without CONFIG_MMU.

It looks to me mmap can work according to Documentation/nommu-mmap.txt. But I'm not sure it's worth to bother.