From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id BE23E6B026C for ; Mon, 12 Nov 2018 05:07:14 -0500 (EST) Received: by mail-ed1-f72.google.com with SMTP id b7so2343433eda.10 for ; Mon, 12 Nov 2018 02:07:14 -0800 (PST) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id w25-v6si848536eju.19.2018.11.12.02.07.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 12 Nov 2018 02:07:13 -0800 (PST) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wACA4oeR114285 for ; Mon, 12 Nov 2018 05:07:12 -0500 Received: from e06smtp01.uk.ibm.com (e06smtp01.uk.ibm.com [195.75.94.97]) by mx0b-001b2d01.pphosted.com with ESMTP id 2nq42289yc-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 12 Nov 2018 05:07:11 -0500 Received: from localhost by e06smtp01.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 12 Nov 2018 10:07:10 -0000 Date: Mon, 12 Nov 2018 15:37:02 +0530 From: Bharata B Rao Subject: Re: [RFC PATCH v1 2/4] kvmppc: Add support for shared pages in HMM driver Reply-To: bharata@linux.ibm.com References: <20181022051837.1165-1-bharata@linux.ibm.com> <20181022051837.1165-3-bharata@linux.ibm.com> <20181101104552.GE16399@350D> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181101104552.GE16399@350D> Message-Id: <20181112100702.GF17399@in.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Balbir Singh Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, linux-mm@kvack.org, paulus@au1.ibm.com, benh@linux.ibm.com, aneesh.kumar@linux.vnet.ibm.com, jglisse@redhat.com, linuxram@us.ibm.com On Thu, Nov 01, 2018 at 09:45:52PM +1100, Balbir Singh wrote: > On Mon, Oct 22, 2018 at 10:48:35AM +0530, Bharata B Rao wrote: > > A secure guest will share some of its pages with hypervisor (Eg. virtio > > bounce buffers etc). Support shared pages in HMM driver. > > > > Signed-off-by: Bharata B Rao > > --- > > arch/powerpc/kvm/book3s_hv_hmm.c | 69 ++++++++++++++++++++++++++++++-- > > 1 file changed, 65 insertions(+), 4 deletions(-) > > > > diff --git a/arch/powerpc/kvm/book3s_hv_hmm.c b/arch/powerpc/kvm/book3s_hv_hmm.c > > index a2ee3163a312..09b8e19b7605 100644 > > --- a/arch/powerpc/kvm/book3s_hv_hmm.c > > +++ b/arch/powerpc/kvm/book3s_hv_hmm.c > > @@ -50,6 +50,7 @@ struct kvmppc_hmm_page_pvt { > > struct hlist_head *hmm_hash; > > unsigned int lpid; > > unsigned long gpa; > > + bool skip_page_out; > > }; > > > > struct kvmppc_hmm_migrate_args { > > @@ -278,6 +279,65 @@ static unsigned long kvmppc_gpa_to_hva(struct kvm *kvm, unsigned long gpa, > > return hva; > > } > > > > +/* > > + * Shares the page with HV, thus making it a normal page. > > + * > > + * - If the page is already secure, then provision a new page and share > > + * - If the page is a normal page, share the existing page > > + * > > + * In the former case, uses the HMM fault handler to release the HMM page. > > + */ > > +static unsigned long > > +kvmppc_share_page(struct kvm *kvm, unsigned long gpa, > > + unsigned long addr, unsigned long page_shift) > > +{ > > + > > So this is a special flag passed via the hypercall to say > this page can be skipped from page_out from secure memory? > Who has the master copy of the page at this point? > > In which case the question is > > Why did we get a fault on the page which resulted in the > fault migration ops being called? > What category of pages are considered shared? When UV/guest asks for sharing a page, there can be two cases: - If the page is already secure, then provision a new page and share - If the page is a normal page, share the existing page In the former case, we touch the page via get_user_pages() and re-use the HMM fault handler to release the HMM page. We use skip_page_out to mark that this page is meant to be released w/o doing a page-out which otherwise would be done if HV touches a secure page. When a page is shared, both HV and UV have mappings to the same physical page that resides in the non-secure memory. Regards, Bharata.