virt/kvm/mmu.rst

55 spte  shadow pte (referring to pfns)
125 A nonleaf spte allows the hardware mmu to reach the leaf pages and
128 A leaf spte corresponds to either one or two translations encoded into
232     parent_ptes bit 0 is zero, only one spte points at this page and
233     parent_ptes points at this single spte, otherwise, there exists multiple
250     Only present on 32-bit hosts, where a 64-bit spte cannot be written
315    - check for valid generation number in the spte (see "Fast invalidation of
334  - walk the shadow page table to find the spte for the translation,
337    - If this is an mmio request, cache the mmio info to the spte and set some
338      reserved bit on the spte (see callers of kvm_mmu_set_mmio_spte_mask)
381 we cannot map the permissions for gpte.u=1, gpte.w=0 to any spte (the
387 - kernel write fault: spte.u=0, spte.w=1 (allows full kernel access,
389 - read fault: spte.u=1, spte.w=0 (allows full read access, disallows kernel
397   the kernel may now execute it.  We handle this by also setting spte.nx.
398   If we get a user fetch or read fault, we'll change spte.u=1 and
399   spte.nx=gpte.nx back.  For this to work, KVM forces EFER.NX to 1 when
407 To prevent an spte that was converted into a kernel page with cr0.wp=0
409 the value of cr0.wp part of the page role.  This means that an spte created
412 exists when an spte created with cr0.wp=0 and cr4.smep=0 is used after
424 To instantiate a large spte, four constraints must be satisfied:
426 - the spte must point to a large host page
429 - if the spte will be writeable, the large page frame may not overlap any
436 a large spte.  The frames at the end of an unaligned memory slot have
453 When KVM finds an MMIO spte, it checks the generation number of the spte.
454 If the generation number of the spte does not equal the global generation
458 Since only 18 bits are used to store generation-number on mmio spte, all
463 stored into the MMIO spte.  Thus, the MMIO spte might be created based on
470 this without losing a bit in the MMIO spte.  The "update in-progress" bit of the
471 generation is not stored in MMIO spte, and is so is implicitly zero when the
472 generation is extracted out of the spte.  If KVM is unlucky and creates an MMIO
473 spte while an update is in-progress, the next access to the spte will always be
476 window closes will have a higher generation number (as compared to the spte).