KVM: x86/mmu: Add "never" option to allow sticky disabling of nx_huge_pages

Add a "never" option to the nx_huge_pages module param to allow userspace
to do a one-way hard disabling of the mitigation, and don't create the
per-VM recovery threads when the mitigation is hard disabled.  Letting
userspace pinky swear that userspace doesn't want to enable NX mitigation
(without reloading KVM) allows certain use cases to avoid the latency
problems associated with spawning a kthread for each VM.

E.g. in FaaS use cases, the guest kernel is trusted and the host may
create 100+ VMs per logical CPU, which can result in 100ms+ latencies when
a burst of VMs is created.

Reported-by: Li RongQing <[email protected]>
Closes: https://lore.kernel.org/all/[email protected]
Cc: Yong He <[email protected]>
Cc: Robert Hoo <[email protected]>
Cc: Kai Huang <[email protected]>
Reviewed-by: Robert Hoo <[email protected]>
Acked-by: Kai Huang <[email protected]>
Tested-by: Luiz Capitulino <[email protected]>
Reviewed-by: Li RongQing <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

0 files changed, 0 insertions, 0 deletions