The cache flush operation in sev guest memory reclaim events was
originally introduced to prevent security issues due to cache
incoherence and untrusted VMM. However when this operation gets
triggered, it causes performance degradation to the whole machine.
This cache flush operation is performed in mmu_notifiers, in particular,
in the mmu_notifier_invalidate_range_start() function, unconditionally
on all guest memory regions. Although the intention was to flush
cache lines only when guest memory was deallocated, the excessive
invocations include many other cases where this flush is unnecessary.
This RFC proposes using the mmu notifier event to determine whether a
cache flush is needed. Specifically, only do the cache flush when the
address range is unmapped, cleared, released or migrated. A bitmap
module param is also introduced to provide flexibility when flush is
needed in more events or no flush is needed depending on the hardware
platform.
Note that the cache flush operation in memory reclamation only targets
SEV/SEV-ES platforms and no cache flush is needed in SEV-SNP VMs.
Therefore the patch series does not apply to the SEV-SNP context.
Jacky Li (4):
KVM: SEV: Drop wbinvd_on_all_cpus() as kvm mmu notifier would flush
the cache
KVM: SEV: Plumb mmu_notifier_event into sev function
KVM: SEV: Limit the call of WBINVDs based on the event type of mmu
notifier
KVM: SEV: Use a bitmap module param to decide whether a cache flush is
needed during the guest memory reclaim
arch/x86/include/asm/kvm_host.h | 3 +-
arch/x86/kvm/svm/sev.c | 62 ++++++++++++++++++++++++---------
arch/x86/kvm/svm/svm.h | 3 +-
arch/x86/kvm/x86.c | 5 +--
include/linux/kvm_host.h | 3 +-
include/linux/mmu_notifier.h | 4 +++
virt/kvm/kvm_main.c | 14 +++++---
7 files changed, 68 insertions(+), 26 deletions(-)
--
2.43.0.rc0.421.g78406f8d94-goog
