From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752793AbeFDMus (ORCPT ); Mon, 4 Jun 2018 08:50:48 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:52252 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752611AbeFDMur (ORCPT ); Mon, 4 Jun 2018 08:50:47 -0400 Date: Mon, 4 Jun 2018 15:50:46 +0300 From: "Michael S. Tsirkin" To: Benjamin Herrenschmidt Cc: David Gibson , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, jasowang@redhat.com, mpe@ellerman.id.au, hch@infradead.org Subject: Re: [RFC V2] virtio: Add platform specific DMA API translation for virito devices Message-ID: <20180604154355-mutt-send-email-mst@kernel.org> References: <20180522063317.20956-1-khandual@linux.vnet.ibm.com> <20180523213703-mutt-send-email-mst@kernel.org> <20180604085742.GQ4251@umbus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 04, 2018 at 07:48:54PM +1000, Benjamin Herrenschmidt wrote: > On Mon, 2018-06-04 at 18:57 +1000, David Gibson wrote: > > > > > - First qemu doesn't know that the guest will switch to "secure mode" > > > in advance. There is no difference between a normal and a secure > > > partition until the partition does the magic UV call to "enter secure > > > mode" and qemu doesn't see any of it. So who can set the flag here ? > > > > This seems weird to me. As a rule HV calls should go through qemu - > > or be allowed to go directly to KVM *by* qemu. > > It's not an HV call, it's a UV call, qemu won't see it, qemu isn't > trusted. Now the UV *will* reflect that to the HV via some synthetized > HV calls, and we *could* have those do a pass by qemu, however, so far, > our entire design doesn't rely on *any* qemu knowledge whatsoever and > it would be sad to add it just for that purpose. It's a temporary work-around. I think that the long-term fix is to support per-device quirks and have the DMA API DTRT for virtio. > Additionally, this is rather orthogonal, see my other email, the > problem we are trying to solve is *not* a qemu problem and it doesn't > make sense to leak that into qemu. > > > We generally reserve > > the latter for hot path things. Since this isn't a hot path, having > > the call handled directly by the kernel seems wrong. > > > > Unless a "UV call" is something different I don't know about. > > Yes, a UV call goes to the Ultravisor, not the Hypervisor. The > Hypervisor isn't trusted. > > > > - Second, when using VIRTIO_F_IOMMU_PLATFORM, we also make qemu (or > > > vhost) go through the emulated MMIO for every access to the guest, > > > which adds additional overhead. > > > Ben.