KVM: VMX: Retry APIC-access page reload if invalidation is in-progress

Re-request an APIC-access page reload if there is a relevant mmu_notifier
invalidation in-progress when KVM retrieves the backing pfn, i.e. stall
vCPUs until the backing pfn for the APIC-access page is "officially"
stable.  Relying on the primary MMU to not make changes after invoking
->invalidate_range() works, e.g. any additional changes to a PRESENT PTE
would also trigger an ->invalidate_range(), but using ->invalidate_range()
to fudge around KVM not honoring past and in-progress invalidations is a
bit hacky.

Honoring invalidations will allow using KVM's standard mmu_notifier hooks
to detect APIC-access page reloads, which will in turn allow removing
KVM's implementation of ->invalidate_range() (the APIC-access page case is
a true one-off).

Opportunistically add a comment to explain why doing nothing if a memslot
isn't found is functionally correct.

Suggested-by: Jason Gunthorpe <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Robin Murphy <[email protected]>
Reviewed-by: Alistair Popple <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

0 files changed, 0 insertions, 0 deletions