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SubjectRe: [PATCH 2/4] KVM: Avoid checking huge page mappings in get_dirty_log()
On Wed, Mar 14, 2012 at 02:34:32PM +0900, Takuya Yoshikawa wrote:
> Marcelo Tosatti <mtosatti@redhat.com> wrote:
>
> > guest fault enable dirty logging
> >
> > tdp_page_fault (all _page_fault functions) kvm_set_memory_region
> >
> >
> > level = mapping_level(vcpu, gfn)
> > (finds level == 2 or 3)
> >
> >
> > rcu_assign_pointer(slot
> > with
> > ->dirty_bitmap)
> > synchronize_srcu_expedited()
>
> Isn't here still in the SRCU read-side critical section?
>
> > schedule()
> > kvm_arch_commit_memory_region()
> > spin_lock(mmu_lock)
> > kvm_mmu_slot_remove_write_access()
> > removes large sptes
> > spin_unlock(mmu_lock)
> > spin_lock(mmu_lock)
> > create large spte accordingly
> > to level above
> > spin_unlock(mmu_lock)
> >
>
> If so, we cannot start kvm_arch_commit_memory_region() until the completion
> of the SRCU critical section and this race will not happen.
>
> Takuya

Correct.



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