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476878e4b2
QEMU running in a stubdom needs to be able to set INTX_DISABLE, and the MSI(-X) enable flags in the PCI config space. This adds an attribute 'allow_interrupt_control' which when set for a PCI device allows writes to this flag(s). The toolstack will need to set this for stubdoms. When enabled, guest (stubdomain) will be allowed to set relevant enable flags, but only one at a time - i.e. it refuses to enable more than one of INTx, MSI, MSI-X at a time. This functionality is needed only for config space access done by device model (stubdomain) serving a HVM with the actual PCI device. It is not necessary and unsafe to enable direct access to those bits for PV domain with the device attached. For PV domains, there are separate protocol messages (XEN_PCI_OP_{enable,disable}_{msi,msix}) for this purpose. Those ops in addition to setting enable bits, also configure MSI(-X) in dom0 kernel - which is undesirable for PCI passthrough to HVM guests. This should not introduce any new security issues since a malicious guest (or stubdom) can already generate MSIs through other ways, see [1] page 8. Additionally, when qemu runs in dom0, it already have direct access to those bits. This is the second iteration of this feature. First was proposed as a direct Xen interface through a new hypercall, but ultimately it was rejected by the maintainer, because of mixing pciback and hypercalls for PCI config space access isn't a good design. Full discussion at [2]. [1]: https://invisiblethingslab.com/resources/2011/Software%20Attacks%20on%20Intel%20VT-d.pdf [2]: https://xen.markmail.org/thread/smpgpws4umdzizze [part of the commit message and sysfs handling] Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com> [the rest] Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> [boris: A few small changes suggested by Roger, some formatting changes] Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> |
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.. | ||
conf_space_capability.c | ||
conf_space_header.c | ||
conf_space_quirks.c | ||
conf_space_quirks.h | ||
conf_space.c | ||
conf_space.h | ||
Makefile | ||
passthrough.c | ||
pci_stub.c | ||
pciback_ops.c | ||
pciback.h | ||
vpci.c | ||
xenbus.c |