| Message ID | 20221110014821.1548347-1-seanjc@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: x86/mmu: Use page-track only for... page tracking | expand |
On Thu, Nov 10, 2022, Sean Christopherson wrote: > Don't bounce through the page-track notifier when zapping+flushing SPTEs > in response to memslot changes as the need to zap+flush isn't strictly > limited to page-tracking. With that done, register KVM's notifier on the > first allocation of a shadow root, as KVM's ->track_write() hook is used > only to react to writes to gPTEs. > > Aside from avoiding a RETPOLINE on emulated writes, dropping KVM's internal > use will allow removing ->track_flush_slot() altogether once KVM-GT moves > to a different hook[*]. Tracking "flushes" of slots is a poor fit for > KVM-GT's needs as KVM-GT needs to drop its write-protection only when a > memslot change is guaranteed to be committed, whereas the "flush" call is > speculative in the sense that KVM may abort a memslot update after flushing > the original memslot. > > https://lore.kernel.org/all/20221108084416.11447-1-yan.y.zhao@intel.com > > Sean Christopherson (2): > KVM: x86/mmu: Don't rely on page-track mechanism to flush on memslot > change > KVM: x86/mmu: Register page-tracker on first shadow root allocation Don't merge this series, I'm going to (hopefully) send a (much larger) v2 that more aggressively cleans up the page tracker APIs, and will replace patch 2 with a completely different patch.
Don't bounce through the page-track notifier when zapping+flushing SPTEs in response to memslot changes as the need to zap+flush isn't strictly limited to page-tracking. With that done, register KVM's notifier on the first allocation of a shadow root, as KVM's ->track_write() hook is used only to react to writes to gPTEs. Aside from avoiding a RETPOLINE on emulated writes, dropping KVM's internal use will allow removing ->track_flush_slot() altogether once KVM-GT moves to a different hook[*]. Tracking "flushes" of slots is a poor fit for KVM-GT's needs as KVM-GT needs to drop its write-protection only when a memslot change is guaranteed to be committed, whereas the "flush" call is speculative in the sense that KVM may abort a memslot update after flushing the original memslot. https://lore.kernel.org/all/20221108084416.11447-1-yan.y.zhao@intel.com Sean Christopherson (2): KVM: x86/mmu: Don't rely on page-track mechanism to flush on memslot change KVM: x86/mmu: Register page-tracker on first shadow root allocation arch/x86/include/asm/kvm_host.h | 1 + arch/x86/kvm/mmu/mmu.c | 24 ++++++++---------------- arch/x86/kvm/x86.c | 2 ++ 3 files changed, 11 insertions(+), 16 deletions(-) base-commit: d663b8a285986072428a6a145e5994bc275df994