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  1. Mar 12, 2021
    • Marc Zyngier's avatar
      KVM: arm64: Reject VM creation when the default IPA size is unsupported · 7d717558
      Marc Zyngier authored
      
      
      KVM/arm64 has forever used a 40bit default IPA space, partially
      due to its 32bit heritage (where the only choice is 40bit).
      
      However, there are implementations in the wild that have a *cough*
      much smaller *cough* IPA space, which leads to a misprogramming of
      VTCR_EL2, and a guest that is stuck on its first memory access
      if userspace dares to ask for the default IPA setting (which most
      VMMs do).
      
      Instead, blundly reject the creation of such VM, as we can't
      satisfy the requirements from userspace (with a one-off warning).
      Also clarify the boot warning, and document that the VM creation
      will fail when an unsupported IPA size is provided.
      
      Although this is an ABI change, it doesn't really change much
      for userspace:
      
      - the guest couldn't run before this change, but no error was
        returned. At least userspace knows what is happening.
      
      - a memory slot that was accepted because it did fit the default
        IPA space now doesn't even get a chance to be registered.
      
      The other thing that is left doing is to convince userspace to
      actually use the IPA space setting instead of relying on the
      antiquated default.
      
      Fixes: 233a7cb2 ("kvm: arm64: Allow tuning the physical address size for VM")
      Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
      Cc: stable@vger.kernel.org
      Reviewed-by: default avatarAndrew Jones <drjones@redhat.com>
      Reviewed-by: default avatarEric Auger <eric.auger@redhat.com>
      Link: https://lore.kernel.org/r/20210311100016.3830038-2-maz@kernel.org
      7d717558
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