From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [RFC PATCH] KVM: PPC: BOOK3S: HV: THP support for guest Date: Tue, 06 May 2014 17:23:18 +0200 Message-ID: <5368FE66.5040809@suse.de> References: <1399224616-25142-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <5368A78D.4070509@suse.de> <1399368400.18906.9.camel@pasglop> <5368ADE3.1050503@suse.de> <87oazbq73t.fsf@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Benjamin Herrenschmidt , paulus@samba.org, linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org To: "Aneesh Kumar K.V" Return-path: Received: from cantor2.suse.de ([195.135.220.15]:40630 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757825AbaEFPXU (ORCPT ); Tue, 6 May 2014 11:23:20 -0400 In-Reply-To: <87oazbq73t.fsf@linux.vnet.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: On 05/06/2014 05:06 PM, Aneesh Kumar K.V wrote: > Alexander Graf writes: > >> On 05/06/2014 11:26 AM, Benjamin Herrenschmidt wrote: >>> On Tue, 2014-05-06 at 11:12 +0200, Alexander Graf wrote: >>> > ..... > > > I updated the commit message as below. Let me know if this is ok. > > KVM: PPC: BOOK3S: HV: THP support for guest This has nothing to do with THP. > > On recent IBM Power CPUs, while the hashed page table is looked up using > the page size from the segmentation hardware (i.e. the SLB), it is > possible to have the HPT entry indicate a larger page size. Thus for > example it is possible to put a 16MB page in a 64kB segment, but since > the hash lookup is done using a 64kB page size, it may be necessary to > put multiple entries in the HPT for a single 16MB page. This > capability is called mixed page-size segment (MPSS). With MPSS, > there are two relevant page sizes: the base page size, which is the > size used in searching the HPT, and the actual page size, which is the > size indicated in the HPT entry. [ Note that the actual page size is > always >= base page size ]. > > We advertise MPSS feature to guest only if the host CPU supports the > same. We use "ibm,segment-page-sizes" device tree node to advertise > the MPSS support. The penc encoding indicate whether we support > a specific combination of base page size and actual page size > in the same segment. It is also the value used in the L|LP encoding > of HPTE entry. > > In-order to support MPSS in guest, KVM need to handle the below details > * advertise MPSS via ibm,segment-page-sizes > * Decode the base and actual page size correctly from the HPTE entry > so that we know what we are dealing with in H_ENTER and and can do Which code path exactly changes for H_ENTER? > the appropriate TLB invalidation in H_REMOVE and evictions. Apart from the grammar (which is pretty broken for the part that is not copied from Paul) and the subject line this sounds quite reasonable. Alex