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

From: Yang Weijiang
Date: Wed Jul 17 2019 - 09:36:35 EST

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:

Previous patch:

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:

V3 -> v4:
1. Modified documentation to make it consistent with patches.
2. Allocated SPPT root page in init_spp() instead of vmx_set_cr3() to
avoid SPPT miss error.
3. Added back co-developers and sign-offs.

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 | 173 ++++++++++
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 | 480 ++++++++++++++++++++++++++
arch/x86/kvm/mmu.h | 1 +
arch/x86/kvm/vmx/capabilities.h | 5 +
arch/x86/kvm/vmx/vmx.c | 129 +++++++
arch/x86/kvm/x86.c | 141 ++++++++
include/linux/kvm_host.h | 9 +
include/uapi/linux/kvm.h | 17 +
13 files changed, 997 insertions(+), 1 deletion(-)
create mode 100644 Documentation/virtual/kvm/spp_kvm.txt