Hello Sergej, On 04/07/16 13:12, Sergej Proskurin wrote:
+/* Reset this p2m table to be empty */ +static void p2m_flush_table(struct p2m_domain *p2m) +{ + struct page_info *top, *pg; + mfn_t mfn; + unsigned int i; + + /* Check whether the p2m table has already been flushed before. */ + if ( p2m->root == NULL) + return; + + spin_lock(&p2m->lock); + + /* + * "Host" p2m tables can have shared entries &c that need a bit more care + * when discarding them + */ + ASSERT(!p2m_is_hostp2m(p2m)); + + /* Zap the top level of the trie */ + top = p2m->root; + + /* Clear all concatenated first level pages */ + for ( i = 0; i < P2M_ROOT_PAGES; i++ ) + { + mfn = _mfn(page_to_mfn(top + i)); + clear_domain_page(mfn); + } + + /* Free the rest of the trie pages back to the paging pool */ + while ( (pg = page_list_remove_head(&p2m->pages)) ) + if ( pg != top ) + { + /* + * Before freeing the individual pages, we clear them to prevent + * reusing old table entries in future p2m allocations. + */ + mfn = _mfn(page_to_mfn(pg)); + clear_domain_page(mfn); + free_domheap_page(pg); + }At this point, we prevent only the first root level page from being freed. In case there are multiple consecutive first level pages, one of them will be freed in the upper loop (and potentially crash the guest if the table is reused at a later point in time). However, testing for every concatenated page in the if clause of the while loop would further decrease the flushing performance. Thus, my question is, whether there is a good way to solve this issue?
The root pages are not part of p2m->pages, so there is no issue. Regards, -- Julien Grall _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
