On 02/06/2012 11:46 AM, Takuya Yoshikawa wrote: > (2012/02/06 12:40), Xiao Guangrong wrote: >> 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. >> > > The victim is not GET_DIRTY_LOG but thread B; it needs to assure the page > is protected before returning. > Ah, right! Reviewed-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx> -- 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
