Re: [RFC PATCH v4 2/4] x86/sgx: Implement support for MADV_WILLNEED

["jarkko@kernel.org" <jarkko@kernel.org>]

On Tue, Feb 14, 2023 at 08:54:53PM +0000, Huang, Kai wrote:
> On Tue, 2023-02-14 at 13:18 -0600, Haitao Huang wrote:
> > Hi Kai
> > 
> > On Tue, 14 Feb 2023 03:47:24 -0600, Huang, Kai <kai.huang@intel.com> wrote:
> > 
> > > On Fri, 2023-01-27 at 20:55 -0800, Haitao Huang wrote:
> > > > @@ -97,10 +99,81 @@ static int sgx_mmap(struct file *file, struct  
> > > > vm_area_struct *vma)
> > > >  	vma->vm_ops = &sgx_vm_ops;
> > > >  	vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> > > >  	vma->vm_private_data = encl;
> > > > +	vma->vm_pgoff = PFN_DOWN(vma->vm_start - encl->base);
> > > >   	return 0;
> > > >  }
> > > 
> > > Perhaps I am missing something, but above change looks weird.  
> > > Conceptually, it doesn't/shouldn't belong to this series, which  
> > > essentially
> > > preallocates and does EAUG EPC pages for a (or part of) given enclave.   
> > > The EAUG
> > > logic should already be working for the normal fault path, which means  
> > > the code
> > > change above either: 1) has been done at other place; 2) isn't needed.
> > > 
> > > I have kinda forgotten the userspace sequence to create an enclave.  If  
> > > I recall
> > > correctly, you do below to create an enclave:
> > > 
> > > 	1) encl_fd = open("/dev/sgx_enclave");
> > > 	2) encl_addr = mmap(encl_fd, encl_size, 0 /* pgoff */);
> > > 	3) IOCTL(ECREATE, encl_addr, encl_size);
> > > 
> > > Would the above code change break the "mmap()" in above step 2?
> > > 	
> > 
> > No, vm_pgoff was not used previously for enclave VMAs. I had to add this  
> > because the offset passed to sgx_fadvise is relative to file base and  
> > calculated in mm/madvise.c like this:
> > 
> >          offset = (loff_t)(start - vma->vm_start)
> >                          + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
> 
> But shouldn't 'offset is relative to the file base' be conceptually correct from
> the fadvice()'s point of view?
> 
> I think you should do:
> 
> 	encl_offset = offset + encl->base;
> 
> inside sgx_fadvice()?

I agree.

BR, Jarkko