On Wed, Jun 03, 2020 at 12:18:44PM +0800, Jason Wang wrote:

On 2020/6/2 下午9:31, Michael S. Tsirkin wrote:

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On Tue, Jun 02, 2020 at 02:49:38PM +0800, Jason Wang wrote:

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On 2020/6/2 下午12:56, Michael S. Tsirkin wrote:

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On Tue, Jun 02, 2020 at 03:22:49AM +0800, kbuild test robot wrote:

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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 seehttps://stackoverflow.com/a/37406982]

url:https://github.com/0day-ci/linux/commits/Jason-Wang/vDPA-doorbell-mapping/20200531-070834
base:https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git  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):
          wgethttps://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross  -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<redacted>

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

drivers/vhost/vdpa.c: In function 'vhost_vdpa_fault':

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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);
|                      ^~~~~~~~~~~~~~~~

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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

     742	
     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;
     751	
     752		notify = ops->get_vq_notification(vdpa, index);
     753	
   > 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;
     759	
     760		return VM_FAULT_NOPAGE;
     761	}
     762	

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.

Thanks

Well

int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
                 unsigned long pfn, unsigned long size, pgprot_t prot)
{
         if (addr != (pfn << PAGE_SHIFT))
                 return -EINVAL;

         vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
         return 0;
}
EXPORT_SYMBOL(remap_pfn_range);


So things aren't going to work if you have a fixed PFN
which is the case of the hardware device.

Looking at the implementation of some drivers e.g mtd_char. If I read the
code correctly, we can do this by providing get_unmapped_area method and use
physical address directly.

But start form CONFIG_MMU should be fine.  Do you prefer making vhost_vdpa
depends on CONFIG_MMU or just fail mmap when CONFIG_MMU is not configured?

Thanks

I'd just not specify the mmap callback at all.

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