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  1. 23 Jan, 2020 4 commits
  3. 21 Jan, 2020 27 commits
  5. 08 Jan, 2020 9 commits
    • Sean Christopherson's avatar
      KVM: x86/mmu: WARN if root_hpa is invalid when handling a page fault · 6948199a
      Sean Christopherson authored 
      WARN if root_hpa is invalid when handling a page fault.  The check on
root_hpa exists for historical reasons that no longer apply to the
current KVM code base.

Remove an equivalent debug-only warning in direct_page_fault(), whose
existence more or less confirms that root_hpa should always be valid
when handling a page fault.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      6948199a
    • Sean Christopherson's avatar
      KVM: x86/mmu: WARN on an invalid root_hpa · 0c7a98e3
      Sean Christopherson authored 
      WARN on the existing invalid root_hpa checks in __direct_map() and
FNAME(fetch).  The "legitimate" path that invalidated root_hpa in the
middle of a page fault is long since gone, i.e. it should no longer be
impossible to invalidate in the middle of a page fault[*].

The root_hpa checks were added by two related commits

  989c6b34 ("KVM: MMU: handle invalid root_hpa at __direct_map")
  37f6a4e2 ("KVM: x86: handle invalid root_hpa everywhere")

to fix a bug where nested_vmx_vmexit() could be called *in the middle*
of a page fault.  At the time, vmx_interrupt_allowed(), which was and
still is used by kvm_can_do_async_pf() via ->interrupt_allowed(),
directly invoked nested_vmx_vmexit() to switch from L2 to L1 to emulate
a VM-Exit on a pending interrupt.  Emulating the nested VM-Exit resulted
in root_hpa being invalidated by kvm_mmu_reset_context() without
explicitly terminating the page fault.

Now that root_hpa is checked for validity by kvm_mmu_page_fault(), WARN
on an invalid root_hpa to detect any flows that reset the MMU while
handling a page fault.  The broken vmx_interrupt_allowed() behavior has
long since been fixed and resetting the MMU during a page fault should
not be considered legal behavior.

[*] It's actually technically possible in FNAME(page_fault)() because it
    calls inject_page_fault() when the guest translation is invalid, but
    in that case the page fault handling is immediately terminated.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      0c7a98e3
    • Sean Christopherson's avatar
      KVM: x86/mmu: Move root_hpa validity checks to top of page fault handler · ddce6208
      Sean Christopherson authored 
      Add a check on root_hpa at the beginning of the page fault handler to
consolidate several checks on root_hpa that are scattered throughout the
page fault code.  This is a preparatory step towards eventually removing
such checks altogether, or at the very least WARNing if an invalid root
is encountered.  Remove only the checks that can be easily audited to
confirm that root_hpa cannot be invalidated between their current
location and the new check in kvm_mmu_page_fault(), and aren't currently
protected by mmu_lock, i.e. keep the checks in __direct_map() and
FNAME(fetch) for the time being.

The root_hpa checks that are consolidate were all added by commit

  37f6a4e2 ("KVM: x86: handle invalid root_hpa everywhere")

which was a follow up to a bug fix for __direct_map(), commit

  989c6b34 ("KVM: MMU: handle invalid root_hpa at __direct_map")

At the time, nested VMX had, in hindsight, crazy handling of nested
interrupts and would trigger a nested VM-Exit in ->interrupt_allowed(),
and thus unexpectedly reset the MMU in flows such as can_do_async_pf().

Now that the wonky nested VM-Exit behavior is gone, the root_hpa checks
are bogus and confusing, e.g. it's not at all obvious what they actually
protect against, and at first glance they appear to be broken since many
of them run without holding mmu_lock.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      ddce6208
    • Sean Christopherson's avatar
      KVM: x86/mmu: Move calls to thp_adjust() down a level · 4cd071d1
      Sean Christopherson authored 
      Move the calls to thp_adjust() down a level from the page fault handlers
to the map/fetch helpers and remove the page count shuffling done in
thp_adjust().

Despite holding a reference to the underlying page while processing a
page fault, the page fault flows don't actually rely on holding a
reference to the page when thp_adjust() is called.  At that point, the
fault handlers hold mmu_lock, which prevents mmu_notifier from completing
any invalidations, and have verified no invalidations from mmu_notifier
have occurred since the page reference was acquired (which is done prior
to taking mmu_lock).

The kvm_release_pfn_clean()/kvm_get_pfn() dance in thp_adjust() is a
quirk that is necessitated because thp_adjust() modifies the pfn that is
consumed by its caller.  Because the page fault handlers call
kvm_release_pfn_clean() on said pfn, thp_adjust() needs to transfer the
reference to the correct pfn purely for correctness when the pfn is
released.

Calling thp_adjust() from __direct_map() and FNAME(fetch) means the pfn
adjustment doesn't change the pfn as seen by the page fault handlers,
i.e. the pfn released by the page fault handlers is the same pfn that
was returned by gfn_to_pfn().
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      4cd071d1
    • Sean Christopherson's avatar
      KVM: x86/mmu: Move transparent_hugepage_adjust() above __direct_map() · 0885904d
      Sean Christopherson authored 
      Move thp_adjust() above __direct_map() in preparation of calling
thp_adjust() from  __direct_map() and FNAME(fetch).

No functional change intended.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      0885904d
    • Sean Christopherson's avatar
      KVM: x86/mmu: Consolidate tdp_page_fault() and nonpaging_page_fault() · 0f90e1c1
      Sean Christopherson authored 
      Consolidate the direct MMU page fault handlers into a common helper,
direct_page_fault().  Except for unique max level conditions, the tdp
and nonpaging fault handlers are functionally identical.

No functional change intended.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      0f90e1c1
    • Sean Christopherson's avatar
      KVM: x86/mmu: Rename lpage_disallowed to account_disallowed_nx_lpage · 2cb70fd4
      Sean Christopherson authored 
      Rename __direct_map()'s param that controls whether or not a disallowed
NX large page should be accounted to match what it actually does.  The
nonpaging_page_fault() case unconditionally passes %false for the param
even though it locally sets lpage_disallowed.

No functional change intended.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      2cb70fd4
    • Sean Christopherson's avatar
      KVM: x86/mmu: Persist gfn_lpage_is_disallowed() to max_level · 2f57b705
      Sean Christopherson authored 
      Persist the max page level calculated via gfn_lpage_is_disallowed() to
the max level "returned" by mapping_level() so that its naturally taken
into account by the max level check that conditions calling
transparent_hugepage_adjust().

Drop the gfn_lpage_is_disallowed() check in thp_adjust() as it's now
handled by mapping_level() and its callers.

Add a comment to document the behavior of host_mapping_level() and its
interaction with max level and transparent huge pages.

Note, transferring the gfn_lpage_is_disallowed() from thp_adjust() to
mapping_level() superficially affects how changes to a memslot's
disallow_lpage count will be handled due to thp_adjust() being run while
holding mmu_lock.

In the more common case where a different vCPU increments the count via
account_shadowed(), gfn_lpage_is_disallowed() is rechecked by set_spte()
to ensure a writable large page isn't created.

In the less common case where the count is decremented to zero due to
all shadow pages in the memslot being zapped, THP behavior now matches
hugetlbfs behavior in the sense that a small page will be created when a
large page could be used if the count reaches zero in the miniscule
window between mapping_level() and acquiring mmu_lock.

Lastly, the new THP behavior also follows hugetlbfs behavior in the
absurdly unlikely scenario of a memslot being moved such that the
memslot's compatibility with respect to large pages changes, but without
changing the validity of the gpf->pfn walk.  I.e. if a memslot is moved
between mapping_level() and snapshotting mmu_seq, it's theoretically
possible to consume a stale disallow_lpage count.  But, since KVM zaps
all shadow pages when moving a memslot and forces all vCPUs to reload a
new MMU, the inserted spte will always be thrown away prior to
completing the memslot move, i.e. whether or not the spte accurately
reflects disallow_lpage is irrelevant.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      2f57b705
    • Sean Christopherson's avatar
      KVM: x86/mmu: Incorporate guest's page level into max level for shadow MMU · cbe1e6f0
      Sean Christopherson authored 
      Restrict the max level for a shadow page based on the guest's level
instead of capping the level after the fact for host-mapped huge pages,
e.g. hugetlbfs pages.  Explicitly capping the max level using the guest
mapping level also eliminates FNAME(page_fault)'s subtle dependency on
THP only supporting 2mb pages.

No functional change intended.
Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      cbe1e6f0
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