KVM: x86/mmu: Allow parallel page faults for the TDP MMU

mainline inclusion
from mainline-v5.12-rc1
commit a2855afc
category: feature
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I7S3VQ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a2855afc7ee88475e8feb16840b23f787bfc994d



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Make the last few changes necessary to enable the TDP MMU to handle page
faults in parallel while holding the mmu_lock in read mode.

Reviewed-by: Peter Feiner <pfeiner@google.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20210202185734.1680553-24-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>