From: Thiago Jung Bauermann <bauerman@linux.ibm.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: Mike Anderson <andmike@linux.ibm.com>,
Michael Roth <mdroth@linux.vnet.ibm.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jean-Philippe Brucker <jean-philippe.brucker@arm.com>,
Jason Wang <jasowang@redhat.com>,
Alexey Kardashevskiy <aik@linux.ibm.com>,
Ram Pai <linuxram@us.ibm.com>,
linux-kernel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org,
Christoph Hellwig <hch@lst.de>
Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted
Date: Wed, 17 Apr 2019 18:42:44 -0300 [thread overview]
Message-ID: <878sw871gr.fsf@morokweng.localdomain> (raw)
In-Reply-To: <20190325005710.GC29295@umbus>
David Gibson <david@gibson.dropbear.id.au> writes:
> On Sat, Mar 23, 2019 at 05:01:35PM -0400, Michael S. Tsirkin wrote:
>> On Thu, Mar 21, 2019 at 09:05:04PM -0300, Thiago Jung Bauermann wrote:
>> > Michael S. Tsirkin <mst@redhat.com> writes:
> [snip]
>> > >> > Is there any justification to doing that beyond someone putting
>> > >> > out slow code in the past?
>> > >>
>> > >> The definition of the ACCESS_PLATFORM flag is generic and captures the
>> > >> notion of memory access restrictions for the device. Unfortunately, on
>> > >> powerpc pSeries guests it also implies that the IOMMU is turned on
>> > >
>> > > IIUC that's really because on pSeries IOMMU is *always* turned on.
>> > > Platform has no way to say what you want it to say
>> > > which is bypass the iommu for the specific device.
>> >
>> > Yes, that's correct. pSeries guests running on KVM are in a gray area
>> > where theoretically they use an IOMMU but in practice KVM ignores it.
>> > It's unfortunate but it's the reality on the ground today. :-/
>
> Um.. I'm not sure what you mean by this. As far as I'm concerned
> there is always a guest-visible (paravirtualized) IOMMU, and that will
> be backed onto the host IOMMU when necessary.
There is, but vhost will ignore it and directly map the guest memory
when ACCESS_PLATFORM (the flag previously known as IOMMU_PLATFORM) isn't
set. From QEMU's hw/virtio/vhost.c:
static int vhost_dev_has_iommu(struct vhost_dev *dev)
{
VirtIODevice *vdev = dev->vdev;
return virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
}
static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr,
hwaddr *plen, int is_write)
{
if (!vhost_dev_has_iommu(dev)) {
return cpu_physical_memory_map(addr, plen, is_write);
} else {
return (void *)(uintptr_t)addr;
}
}
--
Thiago Jung Bauermann
IBM Linux Technology Center
next prev parent reply other threads:[~2019-04-17 21:46 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <87zhrj8kcp.fsf@morokweng.localdomain>
2019-01-29 17:42 ` [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted Thiago Jung Bauermann
2019-01-29 19:02 ` Michael S. Tsirkin
2019-01-30 2:24 ` Jason Wang
2019-01-30 2:36 ` Michael S. Tsirkin
2019-01-30 3:05 ` Jason Wang
2019-01-30 3:26 ` Michael S. Tsirkin
2019-01-30 7:44 ` Christoph Hellwig
2019-02-04 18:15 ` Thiago Jung Bauermann
2019-02-04 21:38 ` Michael S. Tsirkin
2019-02-05 7:24 ` Christoph Hellwig
2019-02-05 16:13 ` Michael S. Tsirkin
2019-03-26 16:53 ` Michael S. Tsirkin
2019-02-04 18:14 ` Thiago Jung Bauermann
2019-02-04 20:23 ` Michael S. Tsirkin
2019-03-20 16:13 ` Thiago Jung Bauermann
2019-03-20 21:17 ` Michael S. Tsirkin
2019-03-22 0:05 ` Thiago Jung Bauermann
2019-03-23 21:01 ` Michael S. Tsirkin
2019-03-25 0:57 ` David Gibson
2019-04-17 21:42 ` Thiago Jung Bauermann [this message]
2019-04-17 21:42 ` Thiago Jung Bauermann
2019-04-19 23:09 ` Michael S. Tsirkin
2019-04-25 1:01 ` Thiago Jung Bauermann
2019-04-25 1:18 ` Michael S. Tsirkin
2019-04-26 23:56 ` Thiago Jung Bauermann
2019-05-20 13:08 ` Michael S. Tsirkin
2019-05-20 13:16 ` Michael S. Tsirkin
2019-06-04 1:13 ` Thiago Jung Bauermann
2019-06-04 1:42 ` Michael S. Tsirkin
2019-06-28 1:58 ` Thiago Jung Bauermann
2019-07-01 14:17 ` Michael S. Tsirkin
2019-07-14 5:51 ` Thiago Jung Bauermann
2019-07-15 14:35 ` Michael S. Tsirkin
2019-07-15 20:29 ` Thiago Jung Bauermann
2019-07-15 20:36 ` Michael S. Tsirkin
2019-07-15 22:03 ` Thiago Jung Bauermann
2019-07-15 22:16 ` Michael S. Tsirkin
2019-07-15 23:05 ` Thiago Jung Bauermann
2019-07-15 23:24 ` Benjamin Herrenschmidt
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