On 02/05/2012 07:42 PM, Takuya Yoshikawa wrote: > From: Takuya Yoshikawa <yoshikawa.takuya@xxxxxxxxxxxxx> > > This patch fixes a race introduced by: > > commit 95d4c16ce78cb6b7549a09159c409d52ddd18dae > KVM: Optimize dirty logging by rmap_write_protect() > > During protecting pages for dirty logging, other threads may also try > to protect a page in mmu_sync_children() or kvm_mmu_get_page(). > > In such a case, because get_dirty_log releases mmu_lock before flushing > TLB's, the following race condition can happen: > > A (get_dirty_log) B (another thread) > > lock(mmu_lock) > clear pte.w > unlock(mmu_lock) > lock(mmu_lock) > pte.w is already cleared > unlock(mmu_lock) > skip TLB flush > return > ... > TLB flush > > Though thread B assumes the page has already been protected when it > returns, the remaining TLB entry will break that assumption. > > This patch fixes this problem by making get_dirty_log hold the mmu_lock > until it flushes the TLB's. > I do not think this is a problem since the dirty page is logged when the writeable spte is being set, and in the end of get_dirty_log, all TLBs are always flushed. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
