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

[Paolo Bonzini]

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