Re: [PATCH RESEND v4 0/9] Enable Sub-page Write Protection Support

Yang Weijiang
2019-08-14T14:00:38Z

On Wed, Aug 14, 2019 at 02:36:30PM +0200, Paolo Bonzini wrote:
> On 14/08/19 09:03, Yang Weijiang wrote:
> > EPT-Based Sub-Page write Protection(SPP)is a HW capability which allows
> > Virtual Machine Monitor(VMM) to specify write-permission for guest
> > physical memory at a sub-page(128 byte) granularity. When this
> > capability is enabled, the CPU enforces write-access check for sub-pages
> > within a 4KB page.
> >
> > The feature is targeted to provide fine-grained memory protection for
> > usages such as device virtualization, memory check-point and VM
> > introspection etc.
> >
> > SPP is active when the "sub-page write protection" (bit 23) is 1 in
> > Secondary VM-Execution Controls. The feature is backed with a Sub-Page
> > Permission Table(SPPT), SPPT is referenced via a 64-bit control field
> > called Sub-Page Permission Table Pointer (SPPTP) which contains a
> > 4K-aligned physical address.
> >
> > Right now, only 4KB physical pages are supported for SPP. To enable SPP
> > for certain physical page, we need to first make the physical page
> > write-protected, then set bit 61 of the corresponding EPT leaf entry.
> > While HW walks EPT, if bit 61 is set, it traverses SPPT with the guset
> > physical address to find out the sub-page permissions at the leaf entry.
> > If the corresponding bit is set, write to sub-page is permitted,
> > otherwise, SPP induced EPT violation is generated.
>
> Still no testcases?
>
> Paolo

Hi, Paolo,
The testcases are included in selftest: https://lkml.org/lkml/2019/6/18/1197