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

[Jason Wang]

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 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<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
> >
> >     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


>