From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bharata B Rao Date: Mon, 12 Nov 2018 10:19:02 +0000 Subject: Re: [RFC PATCH v1 2/4] kvmppc: Add support for shared pages in HMM driver Message-Id: <20181112100702.GF17399@in.ibm.com> List-Id: References: <20181022051837.1165-1-bharata@linux.ibm.com> <20181022051837.1165-3-bharata@linux.ibm.com> <20181101104552.GE16399@350D> In-Reply-To: <20181101104552.GE16399@350D> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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.