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

jarkko
2023-02-17T22:07:56Z

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