Re: [PATCH] KVM: x86: Preserve TDP MMU roots until they are explicitly invalidated

[David Matlack]

On Thu, Apr 13, 2023 at 04:12:51PM -0700, Sean Christopherson wrote:
> Preserve TDP MMU roots until they are explicitly invalidated by gifting
> the TDP MMU itself a reference to a root when it is allocated.  Keeping a
> reference in the TDP MMU fixes a flaw where the TDP MMU exhibits terrible
> performance, and can potentially even soft-hang a vCPU, if a vCPU
> frequently unloads its roots, e.g. when KVM is emulating SMI+RSM.
> 
[...]
> 
> Reported-by: Jeremi Piotrowski <jpiotrowski@xxxxxxxxxxxxxxxxxxx>
> Link: https://lore.kernel.org/all/959c5bce-beb5-b463-7158-33fc4a4f910c@xxxxxxxxxxxxxxxxxxx
> Link: https://lkml.kernel.org/r/20220209170020.1775368-1-pbonzini%40redhat.com
> Link: https://lore.kernel.org/all/20230322013731.102955-1-minipli@xxxxxxxxxxxxxx
> Cc: David Matlack <dmatlack@xxxxxxxxxx>
> Cc: Ben Gardon <bgardon@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>