| Message ID | 20121218163045.3f1c169e.yoshikawa_takuya_b1@lab.ntt.co.jp (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index b7a1235..a32e8cf 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4212,6 +4212,11 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot) for (index = 0; index <= last_index; ++index, ++rmapp) { if (*rmapp) __rmap_write_protect(kvm, rmapp, false); + + if (need_resched() || spin_needbreak(&kvm->mmu_lock)) { + kvm_flush_remote_tlbs(kvm); + cond_resched_lock(&kvm->mmu_lock); + } } }
If the userspace starts dirty logging for a large slot, say 64GB of memory, kvm_mmu_slot_remove_write_access() needs to hold mmu_lock for a long time such as tens of milliseconds. This patch controls the lock hold time by asking the scheduler if we need to reschedule for others. One penalty for this is that we need to flush TLBs before releasing mmu_lock. But since holding mmu_lock for a long time does affect not only the guest, vCPU threads in other words, but also the host as a whole, we should pay for that. In practice, the cost will not be so high because we can protect a fair amount of memory before being rescheduled: on my test environment, cond_resched_lock() was called only once for protecting 12GB of memory even without THP. We can also revisit Avi's "unlocked TLB flush" work later for completely suppressing extra TLB flushes if needed. Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp> --- arch/x86/kvm/mmu.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-)