From: Halil Pasic <pasic@linux.ibm.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
linux-s390@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Viktor Mihajlovski <mihajlov@linux.ibm.com>,
Cornelia Huck <cohuck@redhat.com>, Ram Pai <linuxram@us.ibm.com>,
Thiago Jung Bauermann <bauerman@linux.ibm.com>,
David Gibson <david@gibson.dropbear.id.au>,
"Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
Michael Mueller <mimu@linux.ibm.com>
Subject: Re: [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM
Date: Fri, 21 Feb 2020 14:37:54 +0100 [thread overview]
Message-ID: <20200221143754.7c5f61ff.pasic@linux.ibm.com> (raw)
In-Reply-To: <20200220162747-mutt-send-email-mst@kernel.org>
On Thu, 20 Feb 2020 16:29:50 -0500
"Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Thu, Feb 20, 2020 at 05:06:04PM +0100, Halil Pasic wrote:
> > * This usage is not congruent with standardised semantics of
> > VIRTIO_F_IOMMU_PLATFORM. Guest memory protected is an orthogonal reason
> > for using DMA API in virtio (orthogonal with respect to what is
> > expressed by VIRTIO_F_IOMMU_PLATFORM).
>
> Quoting the spec:
>
> \item[VIRTIO_F_ACCESS_PLATFORM(33)] This feature indicates that
> the device can be used on a platform where device access to data
> in memory is limited and/or translated. E.g. this is the case if the device can be located
> behind an IOMMU that translates bus addresses from the device into physical
> addresses in memory, if the device can be limited to only access
> certain memory addresses or if special commands such as
> a cache flush can be needed to synchronise data in memory with
> the device. Whether accesses are actually limited or translated
> is described by platform-specific means.
> 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.
>
> since device can't access encrypted memory,
> this seems to match your case reasonably well.
>
As David already explained, the device does not have to access encrypted
memory. In fact, we don't have memory encryption but memory protection on
s390. All the device *should* ever see is non-protected memory (one that
was previously shared by the guest).
Our protected guests start as non-protected ones, and may or may not
turn protected during their life-span. From the device perspective,
really, nothing changes. I believe David explained this much better than
I did.
Regards,
Halil
next prev parent reply other threads:[~2020-02-21 13:38 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 16:06 [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM Halil Pasic
2020-02-20 16:06 ` [PATCH 1/2] mm: move force_dma_unencrypted() to mem_encrypt.h Halil Pasic
2020-02-20 16:11 ` Christoph Hellwig
2020-02-20 16:23 ` Christian Borntraeger
2020-02-20 16:31 ` Christoph Hellwig
2020-02-20 17:00 ` Christian Borntraeger
2020-02-21 3:27 ` David Gibson
2020-02-21 13:06 ` Halil Pasic
2020-02-21 15:48 ` Michael S. Tsirkin
2020-02-21 18:07 ` Halil Pasic
2020-02-24 3:33 ` David Gibson
2020-02-24 18:49 ` Halil Pasic
2020-02-25 18:08 ` Cornelia Huck
2020-02-28 0:23 ` David Gibson
2020-02-20 16:06 ` [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected Halil Pasic
2020-02-20 16:13 ` Christoph Hellwig
2020-02-21 2:59 ` David Gibson
2020-02-21 3:41 ` Jason Wang
2020-02-21 13:31 ` Halil Pasic
2020-02-21 13:27 ` Halil Pasic
2020-02-21 16:36 ` Christoph Hellwig
2020-02-24 6:50 ` David Gibson
2020-02-24 18:59 ` Halil Pasic
2020-02-21 14:33 ` Halil Pasic
2020-02-21 16:39 ` Christoph Hellwig
2020-02-21 18:16 ` Halil Pasic
2020-02-22 19:07 ` Michael S. Tsirkin
2020-02-24 17:16 ` Christoph Hellwig
[not found] ` <691d8c8e-665c-b05f-383f-78377fcf6741@amazon.com>
2020-10-28 18:01 ` Michael S. Tsirkin
2020-02-20 20:55 ` Michael S. Tsirkin
2020-02-21 1:17 ` Ram Pai
2020-02-21 3:29 ` David Gibson
2020-02-21 13:12 ` Halil Pasic
2020-02-21 15:39 ` Tom Lendacky
2020-02-24 6:40 ` David Gibson
2020-02-21 15:56 ` Michael S. Tsirkin
2020-02-21 16:35 ` Christoph Hellwig
2020-02-21 18:03 ` Halil Pasic
2020-02-20 20:48 ` [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM Michael S. Tsirkin
2020-02-20 21:29 ` Michael S. Tsirkin
2020-02-21 13:37 ` Halil Pasic [this message]
2020-02-20 21:33 ` Michael S. Tsirkin
2020-02-21 13:49 ` Halil Pasic
2020-02-21 16:41 ` Christoph Hellwig
2020-02-24 5:44 ` David Gibson
2020-02-21 6:22 ` Jason Wang
2020-02-21 14:56 ` Halil Pasic
2020-02-24 3:38 ` David Gibson
2020-02-24 4:01 ` Jason Wang
2020-02-24 6:06 ` Michael S. Tsirkin
2020-02-24 6:45 ` Jason Wang
2020-02-24 7:48 ` Michael S. Tsirkin
2020-02-24 9:26 ` Jason Wang
2020-02-24 13:40 ` Michael S. Tsirkin
2020-02-25 3:38 ` Jason Wang
2020-02-24 13:56 ` Halil Pasic
2020-02-25 3:30 ` Jason Wang
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