Messages in this thread |  | | From | Paolo Bonzini <> | | Subject | [PATCH 00/24] KVM: apply chainsaw to struct kvm_mmu | | Date | Wed, 3 Jun 2026 06:57:50 -0400 |
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The RFC for this series only had minor comments on the naming; probably, everybody liked the idea of doing it and nobody liked the idea of reviewing it front to back. So here it is without the RFC tag.
The kvm_mmu is a "god data structure" that includes three different tasks: describing the guest page table's format, walking the guest page tables and building the page tables. This means that the (already poorly named) nested_mmu is only used in part, since it has no page tables to construct.
Furthermore, some parts are reused across guest and host page tables (such as the reserved bits detector) but others are not; for example permission_fault is replaced by simplified code such as is_executable_pte().
This series cleans this up by splitting kvm_mmu in three parts:
- kvm_pagewalk is the page table walker. There are two of them per vCPU, gva_walk and ngpa_walk. walk_mmu is *always* replaced by a single gva_walk no matter if running an L1 or L2 guest, unlike in the current code that moves it between root_mmu and nested_mmu.
- kvm_mmu retains the page table building functionality. It uses a page table walker to build shadow pages; that is always gva_walk for root_mmu or ngpa_walk for guest_mmu.
- kvm_page_format allows KVM to operate on PTEs that already exist, and merges the code around permission_mask() with the pre-existing struct rsvd_bits_validate. Both kvm_pagewalk and kvm_mmu have their own kvm_page_format, just like struct kvm_mmu had two instances of struct rsvd_bits_validate for gPTE and SPTE reserved bit checks.
The cleanup alone already does something useful, which is to reduce the confusion between guest_mmu and nested_mmu. nested_mmu came to exist long before the introduction of guest_mmu and stole the obvious name, resulting in comments like "Exempt nested MMUs" where the code actually exempts guest_mmu. Renaming guest_mmu could be the next step, though the RFC had multiple opinions about how to do this.
However, the last patch also shows the code reuse benefits can be used for new features too. By adapting the permission_fault() machinery and using it to test SPTEs against struct kvm_page_fault, it makes it possible to support SPTEs that have XS!=XU; these were not supported yet by KVM, but could now be added via memory attributes.
The first five patches are a repost of https://lore.kernel.org/kvm/20260530165545.25599-1-pbonzini@redhat.com/T/ because sashiko does not yet support Based-on tags or similar.
Paolo
RFC->v1: - replaced first four patches with "KVM: x86: small MMU-adjacent cleanups" - renamed cpu_walk and tdp_walk to gva_walk and ngpa_walk (as well as the temporary nested_cpu_walk to ngva_walk)
Paolo Bonzini (24): KVM: x86: remove nested_mmu from mmu_is_nested() KVM: nVMX: remove unnecessary code in prepare_vmcs02_rare KVM: nSVM: invalidate cached PDPTRs across nested NPT transitions KVM: x86: check that kvm_handle_invpcid is only invoked with shadow paging KVM: x86/mmu: move pdptrs out of the MMU KVM: x86/hyperv: remove unnecessary mmu_is_nested() check KVM: x86/mmu: introduce struct kvm_pagewalk KVM: x86/mmu: move get_guest_pgd to struct kvm_pagewalk KVM: x86/mmu: move gva_to_gpa to struct kvm_pagewalk KVM: x86/mmu: move get_pdptr to struct kvm_pagewalk KVM: x86/mmu: move inject_page_fault to struct kvm_pagewalk KVM: x86/mmu: move CPU-related fields to struct kvm_pagewalk KVM: x86/mmu: change CPU-role accessor fields to take struct kvm_pagewalk KVM: x86/mmu: move remaining permission fields to struct kvm_pagewalk KVM: x86/mmu: pass struct kvm_pagewalk to kvm_mmu_invalidate_addr KVM: x86/mmu: change walk_mmu to struct kvm_pagewalk KVM: x86/mmu: change nested_mmu.w to ngva_walk KVM: x86/mmu: make gva_walk a value KVM: x86/mmu: pull struct kvm_pagewalk out of struct kvm_mmu KVM: x86/mmu: cleanup functions that initialize shadow MMU KVM: x86/mmu: pull page format to a new struct KVM: x86/mmu: merge struct rsvd_bits_validate into struct kvm_page_format KVM: x86/mmu: parameterize update_permission_bitmask() KVM: x86/mmu: use kvm_page_format to test SPTEs
arch/x86/include/asm/kvm_host.h | 75 +++--- arch/x86/kvm/hyperv.c | 7 +- arch/x86/kvm/kvm_cache_regs.h | 12 +- arch/x86/kvm/mmu.h | 31 +-- arch/x86/kvm/mmu/mmu.c | 411 +++++++++++++++----------------- arch/x86/kvm/mmu/paging_tmpl.h | 88 +++---- arch/x86/kvm/mmu/spte.c | 4 +- arch/x86/kvm/mmu/spte.h | 64 ++--- arch/x86/kvm/mmu/tdp_mmu.c | 3 +- arch/x86/kvm/svm/nested.c | 40 ++-- arch/x86/kvm/svm/svm.c | 2 +- arch/x86/kvm/vmx/nested.c | 26 +- arch/x86/kvm/vmx/vmx.c | 22 +- arch/x86/kvm/x86.c | 67 +++--- arch/x86/kvm/x86.h | 2 +- 15 files changed, 422 insertions(+), 432 deletions(-)
-- 2.52.0
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