KVM: x86: Optimize mmio spte zapping when creating/moving memslot

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When we create or move a memory slot, we need to zap mmio sptes.
Currently, zap_all() is used for this and this is causing two problems:
 - extra page faults after zapping mmu pages
 - long mmu_lock hold time during zapping mmu pages

For the latter, Marcelo reported a disastrous mmu_lock hold time during
hot-plug, which made the guest unresponsive for a long time.

This patch takes a simple way to fix these problems: do not zap mmu
pages unless they are marked mmio cached.  On our test box, this took
only 50us for the 4GB guest and we did not see ms of mmu_lock hold time
any more.

Note that we still need to do zap_all() for other cases.  So another
work is also needed: Xiao's work may be the one.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@lab.ntt.co.jp>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

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This commit is contained in:

Takuya Yoshikawa 2013-03-12 17:45:30 +09:00 • committed by Gleb Natapov

parent 95b0430d1a

commit 982b3394dd

3 changed files with 20 additions and 1 deletions

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1

arch/x86/include/asm/kvm_host.h

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18

arch/x86/kvm/mmu.c

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2

arch/x86/kvm/x86.c

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