From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andres Lagar-Cavilla Subject: [PATCH 1 of 4] Prevent low values of max_pages for domains doing sharing or paging Date: Wed, 15 Feb 2012 22:57:04 -0500 Message-ID: <11fd4e0a1e1a76ca3bc1.1329364624@xdev.gridcentric.ca> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com Cc: andres@gridcentric.ca, tim@xen.org, adin@gridcentric.ca List-Id: xen-devel@lists.xenproject.org xen/common/domctl.c | 8 +++++++- 1 files changed, 7 insertions(+), 1 deletions(-) Apparently, setting d->max_pages to something lower than d->tot_pages is used as a mechanism for controling a domain's footprint. It will result in all new page allocations failing. This is a really bad idea with paging or sharing, as regular guest memory accesses may need to be satisfied by allocating new memory (either to page in or to unshare). Signed-off-by: Andres Lagar-Cavilla diff -r 62b1fe67b8d1 -r 11fd4e0a1e1a xen/common/domctl.c --- a/xen/common/domctl.c +++ b/xen/common/domctl.c @@ -813,8 +813,14 @@ long do_domctl(XEN_GUEST_HANDLE(xen_domc * NB. We removed a check that new_max >= current tot_pages; this means * that the domain will now be allowed to "ratchet" down to new_max. In * the meantime, while tot > max, all new allocations are disallowed. + * + * Except that this is not a great idea for domains doing sharing or + * paging, as they need to perform new allocations on the fly. */ - d->max_pages = new_max; + if ( (new_max > d->max_pages) || + !((d->mem_event->paging.ring_page != NULL) || + d->arch.hvm_domain.mem_sharing_enabled) ) + d->max_pages = new_max; ret = 0; spin_unlock(&d->page_alloc_lock);