From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [Patch V2] expand x86 arch_shared_info to support linear p2m list Date: Mon, 1 Dec 2014 11:19:39 +0000 Message-ID: <547C4ECB.7070702@citrix.com> References: <1417426153-12893-1-git-send-email-jgross@suse.com> <1417426153-12893-2-git-send-email-jgross@suse.com> <547C4DD6020000780004BA83@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta4.messagelabs.com ([85.158.143.247]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1XvP16-0002Z9-EC for xen-devel@lists.xenproject.org; Mon, 01 Dec 2014 11:19:44 +0000 In-Reply-To: <547C4DD6020000780004BA83@mail.emea.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich , Juergen Gross Cc: keir@xen.org, Ian.Campbell@citrix.com, andrew.cooper3@citrix.com, tim@xen.org, xen-devel@lists.xenproject.org, ian.jackson@eu.citrix.com List-Id: xen-devel@lists.xenproject.org On 01/12/14 10:15, Jan Beulich wrote: >>>> On 01.12.14 at 10:29, wrote: >> The x86 struct arch_shared_info field pfn_to_mfn_frame_list_list >> currently contains the mfn of the top level page frame of the 3 level >> p2m tree, which is used by the Xen tools during saving and restoring >> (and live migration) of pv domains and for crash dump analysis. With >> three levels of the p2m tree it is possible to support up to 512 GB of >> RAM for a 64 bit pv domain. >> >> A 32 bit pv domain can support more, as each memory page can hold 1024 >> instead of 512 entries, leading to a limit of 4 TB. >> >> To be able to support more RAM on x86-64 switch to a virtual mapped >> p2m list. >> >> This patch expands struct arch_shared_info with a new p2m list virtual >> address, the root of the page table root and a p2m generation count. >> The new information is indicated by the domain to be valid by storing >> ~0UL into pfn_to_mfn_frame_list_list. The hypervisor indicates >> usability of this feature by a new flag XENFEAT_virtual_p2m. >> >> Right now XENFEAT_virtual_p2m will not be set. This will change when >> the Xen tools support the virtual mapped p2m list. > > This seems wrong: XENFEAT_* only reflect hypervisor capabilities. > I.e. the availability of the new functionality may need to be > advertised another way - xenstore perhaps? Xenstore doesn't work for dom0. Shouldn't this be something the guest kernel reports using a ELF note bit? When building a domain (either in Xen for dom0 or in the tools), the builder may provide a linear p2m iff supported by the guest kernel and then (and only then) can it provide a guest with > 512 GiB. David