Re: [PATCH RFC 00/10] Intel EPT-Based Sub-page Write Protection Support.

[Yi Zhang <yi.z.zhang@linux.intel.com>]

On 2017-10-20 at 20:06:47 +0300, Mihai Donțu wrote:
> On Fri, 2017-10-20 at 16:47 +0800, Yi Zhang wrote:
> > Could you mind to provide more information and history about your
> > investigation?
> 
> We are using VMI to secure certain parts of a guest kernel in memory
> (like prevent a certain data structure from being overriten). However,
> it sometimes happens for that part to be placed in the same page with
> other data, of no interest to us, that gets written frequently. This
> makes using the EPT problematic (a 4k page is just too big and
> generates too many violations). However, SPP (with its 128 bytes
> granularity) is ideal here.
> 

> > > Also, if Intel doesn't have a specific use case for it that requires
> > > separate access to SPP control, then maybe we can fold it into the VMI 
> > > API we are working on?
> > 
> > That's totally Excellent as we really don't have a specific user case at
> > this time.
> 
> OK. We will spend some time thinking at a proper way of exposing SPP
> with the VMI API.
> 
> For example, we now work on implementing something similar to this:
> 
>   kvm_set_page_access( struct kvm *kvm, gfn_t gfn, u8 access );
> 
> The simplest approach would be to add something like:
> 
>   kvm_set_sub_page_access( struct kvm *kvm, gfn_t gfn, u32 mask );
> 
> where every bit from 'mask' indicates the write-allowed state of every
> 128-byte subpage.

Got it, seems very compatible with current implementation by us. 
> 
> > BTW, I have already submit the SPP implementation draft in Xen side.
> > when you got some time, you can take a look at if that match your
> > requirement.
> 
> I believe my colleague Răzvan Cojocaru has already commented on that
> patch set. :-)

Oh, yes, pls send my best thanks to him. 

> 
> -- 
> Mihai Donțu
>