Re: [PATCH v3 0/9] Enable Sub-page Write Protection Support

[Yang Weijiang]

On Fri, Jun 07, 2019 at 03:27:01PM +0200, Paolo Bonzini wrote:
> On 06/06/19 17:28, 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 vilation is generated.
> > 
> > Please refer to the SPP introduction document in this patch set and Intel SDM
> > for details:
> > 
> > Intel SDM:
> > https://software.intel.com/sites/default/files/managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf
> > 
> > Previous patch:
> > https://lkml.org/lkml/2018/11/30/605
> > 
> > Patch 1: Introduction to SPP.
> > Patch 2: Add SPP related flags and control bits.
> > Patch 3: Functions for SPPT setup.
> > Patch 4: Add SPP access bitmaps for memslots.
> > Patch 5: Low level implementation of SPP operations.
> > Patch 6: Implement User space access IOCTLs.
> > Patch 7: Handle SPP induced VMExit and EPT violation.
> > Patch 8: Enable lazy mode SPPT setup.
> > Patch 9: Handle memory remapping and reclaim.
> > 
> > 
> > Change logs:
> > 
> > V2 - V3:                                                                
> >  1. Rebased patches to kernel 5.1 release                                
> >  2. Deferred SPPT setup to EPT fault handler if the page is not available
> >     while set_subpage() is being called.                                 
> >  3. Added init IOCTL to reduce extra cost if SPP is not used.            
> >  4. Refactored patch structure, cleaned up cross referenced functions.    
> >  5. Added code to deal with memory swapping/migration/shrinker cases.    
> >                                                                            
> > V2 - V1:                                                                
> >  1. Rebased to 4.20-rc1                                                  
> >  2. Move VMCS change to a separated patch.                               
> >  3. Code refine and Bug fix 
> > 
> > 
> > Yang Weijiang (9):
> >   Documentation: Introduce EPT based Subpage Protection
> >   KVM: VMX: Add control flags for SPP enabling
> >   KVM: VMX: Implement functions for SPPT paging setup
> >   KVM: VMX: Introduce SPP access bitmap and operation functions
> >   KVM: VMX: Add init/set/get functions for SPP
> >   KVM: VMX: Introduce SPP user-space IOCTLs
> >   KVM: VMX: Handle SPP induced vmexit and page fault
> >   KVM: MMU: Enable Lazy mode SPPT setup
> >   KVM: MMU: Handle host memory remapping and reclaim
> > 
> >  Documentation/virtual/kvm/spp_kvm.txt | 216 ++++++++++++
> >  arch/x86/include/asm/cpufeatures.h    |   1 +
> >  arch/x86/include/asm/kvm_host.h       |  26 +-
> >  arch/x86/include/asm/vmx.h            |  10 +
> >  arch/x86/include/uapi/asm/vmx.h       |   2 +
> >  arch/x86/kernel/cpu/intel.c           |   4 +
> >  arch/x86/kvm/mmu.c                    | 469 ++++++++++++++++++++++++++
> >  arch/x86/kvm/mmu.h                    |   1 +
> >  arch/x86/kvm/vmx/capabilities.h       |   5 +
> >  arch/x86/kvm/vmx/vmx.c                | 138 ++++++++
> >  arch/x86/kvm/x86.c                    | 141 ++++++++
> >  include/linux/kvm_host.h              |   9 +
> >  include/uapi/linux/kvm.h              |  17 +
> >  13 files changed, 1038 insertions(+), 1 deletion(-)
> >  create mode 100644 Documentation/virtual/kvm/spp_kvm.txt
> > 
> 
> Please add testcases in tools/testing/selftests/kvm.
> 
> Paolo
Hi, Paolo,
Selftest patch for SPP has been released to community,
please check and review, thanks!