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Diffstat (limited to 'Documentation/virt/kvm/x86/mmu.rst')
| -rw-r--r-- | Documentation/virt/kvm/x86/mmu.rst | 49 |
1 files changed, 37 insertions, 12 deletions
diff --git a/Documentation/virt/kvm/x86/mmu.rst b/Documentation/virt/kvm/x86/mmu.rst index 8739120f4300..2b3b6d442302 100644 --- a/Documentation/virt/kvm/x86/mmu.rst +++ b/Documentation/virt/kvm/x86/mmu.rst @@ -202,10 +202,22 @@ Shadow pages contain the following information: Is 1 if the MMU instance cannot use A/D bits. EPT did not have A/D bits before Haswell; shadow EPT page tables also cannot use A/D bits if the L1 hypervisor does not enable them. + role.guest_mode: + Indicates the shadow page is created for a nested guest. role.passthrough: The page is not backed by a guest page table, but its first entry points to one. This is set if NPT uses 5-level page tables (host - CR4.LA57=1) and is shadowing L1's 4-level NPT (L1 CR4.LA57=1). + CR4.LA57=1) and is shadowing L1's 4-level NPT (L1 CR4.LA57=0). + mmu_valid_gen: + The MMU generation of this page, used to fast zap of all MMU pages within a + VM without blocking vCPUs too long. Specifically, KVM updates the per-VM + valid MMU generation which causes the mismatch of mmu_valid_gen for each mmu + page. This makes all existing MMU pages obsolete. Obsolete pages can't be + used. Therefore, vCPUs must load a new, valid root before re-entering the + guest. The MMU generation is only ever '0' or '1'. Note, the TDP MMU doesn't + use this field as non-root TDP MMU pages are reachable only from their + owning root. Thus it suffices for TDP MMU to use role.invalid in root pages + to invalidate all MMU pages. gfn: Either the guest page table containing the translations shadowed by this page, or the base page frame for linear translations. See role.direct. @@ -219,21 +231,30 @@ Shadow pages contain the following information: at __pa(sp2->spt). sp2 will point back at sp1 through parent_pte. The spt array forms a DAG structure with the shadow page as a node, and guest pages as leaves. - gfns: - An array of 512 guest frame numbers, one for each present pte. Used to - perform a reverse map from a pte to a gfn. When role.direct is set, any - element of this array can be calculated from the gfn field when used, in - this case, the array of gfns is not allocated. See role.direct and gfn. - root_count: - A counter keeping track of how many hardware registers (guest cr3 or - pdptrs) are now pointing at the page. While this counter is nonzero, the - page cannot be destroyed. See role.invalid. + shadowed_translation: + An array of 512 shadow translation entries, one for each present pte. Used + to perform a reverse map from a pte to a gfn as well as its access + permission. When role.direct is set, the shadow_translation array is not + allocated. This is because the gfn contained in any element of this array + can be calculated from the gfn field when used. In addition, when + role.direct is set, KVM does not track access permission for each of the + gfn. See role.direct and gfn. + root_count / tdp_mmu_root_count: + root_count is a reference counter for root shadow pages in Shadow MMU. + vCPUs elevate the refcount when getting a shadow page that will be used as + a root page, i.e. page that will be loaded into hardware directly (CR3, + PDPTRs, nCR3 EPTP). Root pages cannot be destroyed while their refcount is + non-zero. See role.invalid. tdp_mmu_root_count is similar but exclusively + used in TDP MMU as an atomic refcount. parent_ptes: The reverse mapping for the pte/ptes pointing at this page's spt. If parent_ptes bit 0 is zero, only one spte points at this page and parent_ptes points at this single spte, otherwise, there exists multiple sptes pointing at this page and (parent_ptes & ~0x1) points at a data structure with a list of parent sptes. + ptep: + The kernel virtual address of the SPTE that points at this shadow page. + Used exclusively by the TDP MMU, this field is a union with parent_ptes. unsync: If true, then the translations in this page may not match the guest's translation. This is equivalent to the state of the tlb when a pte is @@ -245,7 +266,7 @@ Shadow pages contain the following information: unsynchronized children). unsync_child_bitmap: A bitmap indicating which sptes in spt point (directly or indirectly) at - pages that may be unsynchronized. Used to quickly locate all unsychronized + pages that may be unsynchronized. Used to quickly locate all unsynchronized pages reachable from a given page. clear_spte_count: Only present on 32-bit hosts, where a 64-bit spte cannot be written @@ -261,6 +282,10 @@ Shadow pages contain the following information: since the last time the page table was actually used; if emulation is triggered too frequently on this page, KVM will unmap the page to avoid emulation in the future. + tdp_mmu_page: + Is 1 if the shadow page is a TDP MMU page. This variable is used to + bifurcate the control flows for KVM when walking any data structure that + may contain pages from both TDP MMU and shadow MMU. Reverse map =========== @@ -377,7 +402,7 @@ Emulating cr0.wp ================ If tdp is not enabled, the host must keep cr0.wp=1 so page write protection -works for the guest kernel, not guest guest userspace. When the guest +works for the guest kernel, not guest userspace. When the guest cr0.wp=1, this does not present a problem. However when the guest cr0.wp=0, we cannot map the permissions for gpte.u=1, gpte.w=0 to any spte (the semantics require allowing any guest kernel access plus user read access). |