KVM: x86: Retry page fault if MMU reload is pending and root has no sp
Play nice with a NULL shadow page when checking for an obsolete root in the page fault handler by flagging the page fault as stale if there's no shadow page associated with the root and KVM_REQ_MMU_RELOAD is pending. Invalidating memslots, which is the only case where _all_ roots need to be reloaded, requests all vCPUs to reload their MMUs while holding mmu_lock for lock. The "special" roots, e.g. pae_root when KVM uses PAE paging, are not backed by a shadow page. Running with TDP disabled or with nested NPT explodes spectaculary due to dereferencing a NULL shadow page pointer. Skip the KVM_REQ_MMU_RELOAD check if there is a valid shadow page for the root. Zapping shadow pages in response to guest activity, e.g. when the guest frees a PGD, can trigger KVM_REQ_MMU_RELOAD even if the current vCPU isn't using the affected root. I.e. KVM_REQ_MMU_RELOAD can be seen with a completely valid root shadow page. This is a bit of a moot point as KVM currently unloads all roots on KVM_REQ_MMU_RELOAD, but that will be cleaned up in the future. Fixes: a955cad8 ("KVM: x86/mmu: Retry page fault if root is invalidated by memslot update") Cc: stable@vger.kernel.org Cc: Maxim Levitsky <mlevitsk@redhat.com> Signed-off-by:Sean Christopherson <seanjc@google.com> Message-Id: <20211209060552.2956723-2-seanjc@google.com> Signed-off-by: