Re: [PATCH V2 16/32] x86/sgx: Support restricting of enclave page permissions

[Jarkko Sakkinen]

On Sat, Mar 05, 2022 at 05:19:24AM +0200, Jarkko Sakkinen wrote:
> Sorry, I missed this.
> 
> On Thu, Mar 03, 2022 at 01:44:14PM -0800, Dave Hansen wrote:
> > On 3/3/22 13:23, Reinette Chatre wrote:
> > > Unfortunately MAP_POPULATE is not supported by SGX VMAs because of their
> > > VM_IO and VM_PFNMAP flags. When VMAs with such flags obtain this capability
> > > then I believe that SGX would benefit.
> > 
> > Some Intel folks asked for this quite a while ago.  I think it's
> > entirely doable: add a new vm_ops->populate() function that will allow
> > ignoring VM_IO|VM_PFNMAP if present.
> 
> I'm sorry what I don't understand what you mean by ignoring here,
> i.e. cannot fully comprehend the last sentece.
> 
> And would the vm_ops->populate() be called right after the existing ones
> involved with the VMA creation process?
> 
> > Or, if nobody wants to waste all of the vm_ops space, just add an
> > arch_vma_populate() or something which can call over into SGX.
> > 
> > I'll happily review the patches if anyone can put such a beast together.
> 
> I'll start with vm_ops->populate() and check the feedback first for
> that.

I would instead extend populate() in file_operations into:

int (*populate)(struct file *, struct vm_area_struct *, bool populate);

This does not add to memory consumption.

BR, Jarkko