On Wed, Jan 30, 2019 at 10:24:01AM +0800, Jason Wang wrote: > > On 2019/1/30 上午3:02, Michael S. Tsirkin wrote: > > On Tue, Jan 29, 2019 at 03:42:44PM -0200, Thiago Jung Bauermann wrote: > > > Fixing address of powerpc mailing list. > > > > > > Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx> writes: > > > > > > > Hello, > > > > > > > > With Christoph's rework of the DMA API that recently landed, the patch > > > > below is the only change needed in virtio to make it work in a POWER > > > > secure guest under the ultravisor. > > > > > > > > The other change we need (making sure the device's dma_map_ops is NULL > > > > so that the dma-direct/swiotlb code is used) can be made in > > > > powerpc-specific code. > > > > > > > > Of course, I also have patches (soon to be posted as RFC) which hook up > > > > <linux/mem_encrypt.h> to the powerpc secure guest support code. > > > > > > > > What do you think? > > > > > > > > From d0629a36a75c678b4a72b853f8f7f8c17eedd6b3 Mon Sep 17 00:00:00 2001 > > > > From: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx> > > > > Date: Thu, 24 Jan 2019 22:08:02 -0200 > > > > Subject: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted > > > > > > > > The host can't access the guest memory when it's encrypted, so using > > > > regular memory pages for the ring isn't an option. Go through the DMA API. > > > > > > > > Signed-off-by: Thiago Jung Bauermann <bauerman@xxxxxxxxxxxxx> > > Well I think this will come back to bite us (witness xen which is now > > reworking precisely this path - but at least they aren't to blame, xen > > came before ACCESS_PLATFORM). > > > > I also still think the right thing would have been to set > > ACCESS_PLATFORM for all systems where device can't access all memory. > > > > But I also think I don't have the energy to argue about power secure > > guest anymore. So be it for power secure guest since the involved > > engineers disagree with me. Hey I've been wrong in the past ;). > > > > But the name "sev_active" makes me scared because at least AMD guys who > > were doing the sensible thing and setting ACCESS_PLATFORM (unless I'm > > wrong? I reemember distinctly that's so) will likely be affected too. > > We don't want that. > > > > So let's find a way to make sure it's just power secure guest for now > > pls. > > > > I also think we should add a dma_api near features under virtio_device > > such that these hacks can move off data path. > > > Anyway the current Xen code is conflict with spec which said: > > "If this feature bit is set to 0, then the device has same access to memory > addresses supplied to it as the driver has. In particular, the device will > always use physical addresses matching addresses used by the driver > (typically meaning physical addresses used by the CPU) and not translated > further, and can access any address supplied to it by the driver. When > clear, this overrides any platform-specific description of whether device > access is limited or translated in any way, e.g. whether an IOMMU may be > present. " > > I wonder how much value that the above description can give us. It's kind of > odd that the behavior of "when the feature is not negotiated" is described > in the spec. Hmm what's odd about it? We need to describe the behaviour is all cases. > Personally I think we can remove the above and then we can > switch to use DMA API unconditionally in guest driver. It may have single > digit regression probably, we can try to overcome it. > > Thanks This has been discussed ad nauseum. virtio is all about compatibility. Losing a couple of lines of code isn't worth breaking working setups. People that want "just use DMA API no tricks" now have the option. Setting a flag in a feature bit map is literally a single line of code in the hypervisor. So stop pushing for breaking working legacy setups and just fix it in the right place. > > > > > By the way could you please respond about virtio-iommu and > > why there's no support for ACCESS_PLATFORM on power? > > > > I have Cc'd you on these discussions. > > > > > > Thanks! > > > > > > > > --- > > > > drivers/virtio/virtio_ring.c | 5 ++++- > > > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > > > > index cd7e755484e3..321a27075380 100644 > > > > --- a/drivers/virtio/virtio_ring.c > > > > +++ b/drivers/virtio/virtio_ring.c > > > > @@ -259,8 +259,11 @@ static bool vring_use_dma_api(struct virtio_device *vdev) > > > > * not work without an even larger kludge. Instead, enable > > > > * the DMA API if we're a Xen guest, which at least allows > > > > * all of the sensible Xen configurations to work correctly. > > > > + * > > > > + * Also, if guest memory is encrypted the host can't access > > > > + * it directly. In this case, we'll need to use the DMA API. > > > > */ > > > > - if (xen_domain()) > > > > + if (xen_domain() || sev_active()) > > > > return true; > > > > > > > > return false; > > > > > > -- > > > Thiago Jung Bauermann > > > IBM Linux Technology Center _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
