Re: [RFC PATCH V2 00/11] Intel EPT-Based Sub-page Protection Support

[Yi Zhang]

On 2018-12-03 at 05:56:13 +0200, Mihai DonÈu wrote:
> Hi Paolo,
> 
> On Fri, 2018-11-30 at 11:07 +0100, Paolo Bonzini wrote:
> > On 30/11/18 08:52, Zhang Yi wrote:
> > > Here is a patch-series which adding EPT-Based Sub-page Write Protection Support.
> > > 
> > > Introduction:
> > > 
> > > EPT-Based Sub-page Write Protection referred to as SPP, it is a capability which
> > > allow Virtual Machine Monitors(VMM) to specify write-permission for guest
> > > physical memory at a sub-page(128 byte) granularity.  When this capability is
> > > utilized, the CPU enforces write-access permissions for sub-page regions of 4K
> > > pages as specified by the VMM. EPT-based sub-page permissions is intended to
> > > enable fine-grained memory write enforcement by a VMM for security(guest OS
> > > monitoring) and usages such as device virtualization and memory check-point.
> > > 
> > > SPPT is active when the "sub-page write protection" VM-execution control is 1.
> > > SPPT looks up the guest physical addresses to derive a 64 bit "sub-page
> > > permission" value containing sub-page write permissions. The lookup from
> > > guest-physical addresses to the sub-page region permissions is determined by a
> > > set of SPPT paging structures.
> > > 
> > > When the "sub-page write protection" VM-execution control is 1, the SPPT is used
> > > to lookup write permission bits for the 128 byte sub-page regions containing in
> > > the 4KB guest physical page. EPT specifies the 4KB page level privileges that
> > > software is allowed when accessing the guest physical address, whereas SPPT
> > > defines the write permissions for software at the 128 byte granularity regions
> > > within a 4KB page. Write accesses prevented due to sub-page permissions looked
> > > up via SPPT are reported as EPT violation VM exits. Similar to EPT, a logical
> > > processor uses SPPT to lookup sub-page region write permissions for
> > > guest-physical addresses only when those addresses are used to access memory.
> > 
> > Hi,
> > 
> > I think the right thing to do here would be to first get VM
> > introspection in KVM, as SPP is mostly an introspection feature and it
> > should be controller by the introspector rather than the KVM userspace.
> > 
> > Mihai, if you resubmit, I promise that I will look at it promptly.
Thanks review, Paolo, What do u think we cook some user-cases for qemu or
some kvmtools? even with some other kernel hyper-calls?

SPP is not only an introspection depended features.
> 
> I'm currently traveling until Wednesday, but when I'll get into the
> office I will see about preparing a new patch set and send it to the
> list before Christmas.
Thanks Mihai, please include me in the new VMI patch set. 
> 
> Regards,
> 
> -- 
> Mihai DonÈu
>