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KVM: MMU: Don't use RCU for lockless shadow walking

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Using RCU for lockless shadow walking can increase the amount of memory
in use by the system, since RCU grace periods are unpredictable.  We also
have an unconditional write to a shared variable (reader_counter), which
isn't good for scaling.

Replace that with a scheme similar to x86's get_user_pages_fast(): disable
interrupts during lockless shadow walk to force the freer
(kvm_mmu_commit_zap_page()) to wait for the TLB flush IPI to find the
processor with interrupts enabled.

We also add a new vcpu->mode, READING_SHADOW_PAGE_TABLES, to prevent
kvm_flush_remote_tlbs() from avoiding the IPI.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Avi Kivity 2012-05-14 15:44:06 +03:00 • committed by Marcelo Tosatti
parent b2da15ac26
commit c142786c62
3 changed files with 31 additions and 49 deletions
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3
include/linux/kvm_host.h
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@ -128,7 +128,8 @@ int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
enum {
OUTSIDE_GUEST_MODE,
IN_GUEST_MODE,
EXITING_GUEST_MODE
EXITING_GUEST_MODE,
READING_SHADOW_PAGE_TABLES,
};
/*