Re: [PATCH 2/2] virtio_ring: Use DMA API if memory is encrypted

[David Gibson]

On Tue, Oct 15, 2019 at 09:35:01AM +0200, Christoph Hellwig wrote:
> On Fri, Oct 11, 2019 at 06:25:19PM -0700, Ram Pai wrote:
> > From: Thiago Jung Bauermann 
> > 
> > Normally, virtio enables DMA API with VIRTIO_F_IOMMU_PLATFORM, which must
> > be set by both device and guest driver. However, as a hack, when DMA API
> > returns physical addresses, guest driver can use the DMA API; even though
> > device does not set VIRTIO_F_IOMMU_PLATFORM and just uses physical
> > addresses.
> 
> Sorry, but this is a complete bullshit hack.  Driver must always use
> the DMA API if they do DMA, and if virtio devices use physical addresses
> that needs to be returned through the platform firmware interfaces for
> the dma setup.  If you don't do that yet (which based on previous
> informations you don't), you need to fix it, and we can then quirk
> old implementations that already are out in the field.
> 
> In other words: we finally need to fix that virtio mess and not pile
> hacks on top of hacks.

Christoph, if I understand correctly, your objection isn't so much to
the proposed change here of itself, except insofar as it entrenches
virtio's existing code allowing it to either use the DMA api or bypass
it and use physical addresses directly.  Is that right, or have I
missed something?

Where do you envisage the decision to bypass the IOMMU being made?
The virtio spec more or less states that virtio devices use hypervisor
magic to access physical addresses directly, rather than using normal
DMA channels.  The F_IOMMU_PLATFORM flag then overrides that, since it
obviously won't work for hardware devices.

The platform code isn't really in a position to know that virtio
devices are (usually) magic.  So were you envisaging the virtio driver
explicitly telling the platform to use bypassing DMA operations?

-- 
David Gibson| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson


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[PATCH] iommu/amd: Apply the same IVRS IOAPIC workaround to Acer Aspire A315-41

[Takashi Iwai]

Acer Aspire A315-41 requires the very same workaround as the existing
quirk for Dell Latitude 5495.  Add the new entry for that.

BugLink: https://bugzilla.suse.com/show_bug.cgi?id=1137799
Signed-off-by: Takashi Iwai 
---
 drivers/iommu/amd_iommu_quirks.c | 13 +
 1 file changed, 13 insertions(+)

diff --git a/drivers/iommu/amd_iommu_quirks.c b/drivers/iommu/amd_iommu_quirks.c
index c235f79b7a20..5120ce4fdce3 100644
--- a/drivers/iommu/amd_iommu_quirks.c
+++ b/drivers/iommu/amd_iommu_quirks.c
@@ -73,6 +73,19 @@ static const struct dmi_system_id ivrs_quirks[] __initconst 
= {
},
.driver_data = (void *)_ioapic_quirks[DELL_LATITUDE_5495],
},
+   {
+   /*
+* Acer Aspire A315-41 requires the very same workaround as
+* Dell Latitude 5495
+*/
+   .callback = ivrs_ioapic_quirk_cb,
+   .ident = "Acer Aspire A315-41",
+   .matches = {
+   DMI_MATCH(DMI_SYS_VENDOR, "Acer"),
+   DMI_MATCH(DMI_PRODUCT_NAME, "Aspire A315-41"),
+   },
+   .driver_data = (void *)_ioapic_quirks[DELL_LATITUDE_5495],
+   },
{
.callback = ivrs_ioapic_quirk_cb,
.ident = "Lenovo ideapad 330S-15ARR",
-- 
2.16.4