On 02/25/2016 04:49 PM, Paolo Bonzini wrote:
On 25/02/2016 08:35, Xiao Guangrong wrote:
This may release the mmu_lock before committing the zapping.
Is it safe? If so, we may want to see the reason in the changelog.
It is unsafe indeed, please do not do it.
Can you explain why? kvm_zap_obsolete_pages does the same.
It's not the same, please see the comment in kvm_mmu_invalidate_zap_all_pages:
/*
* Notify all vcpus to reload its shadow page table
* and flush TLB. Then all vcpus will switch to new
* shadow page table with the new mmu_valid_gen.
*
* Note: we should do this under the protection of
* mmu-lock, otherwise, vcpu would purge shadow page
* but miss tlb flush.
*/
kvm_reload_remote_mmus(kvm);
That means the tlb is flushed before releasing mmu-lock.
A example is in rmap_write_protect(), when KVM creates a shadow page table for
the the guest, it detects no spte pointing to the gfn, so tlb is not flushed so
that guest can freely updates its pte.
