On Fri, May 17, 2019 at 04:01:29PM -0300, Eduardo Habkost wrote: > Hi, > > Sorry for taking so long to look at this more closely: > > On Fri, Feb 15, 2019 at 10:32:38AM +0000, Daniel P. Berrangé wrote: > > A number of virtio devices (gpu, crypto, mouse, keyboard, tablet) only > > support the virtio-1 (aka modern) mode. Currently if the user launches > > QEMU, setting those devices to enable legacy mode, QEMU will silently > > create them in modern mode, ignoring the user's (mistaken) request. > > > > This patch introduces proper data validation so that an attempt to > > configure a virtio-1-only devices in legacy mode gets reported as an > > error to the user. > > > > Checking this required introduction of a new field to explicitly track > > what operating model is to be used for a device, separately from the > > disable_modern and disable_legacy fields that record the user's > > requested configuration. > > I'm still trying to understand why we need to add a new field. > > If disable_modern, disable_legacy and mode are always expected to > be consistent with each other, why do we need another field? > > If they are not always consistent with each other, when exactly > do we want them to be inconsistent, and why?
The pain point is that we're using the existing variables to record two distinct pieces of information - The user's request for modern vs legacy - The PCI bus requirements for modern vs legacy The existing code would overwrite the user's setting for "disable_legacy" when deciding whether the device is in a PCI or PCIe port. This happens in virtio_pci_realize. We can only report errors with the user's requested config after the sub-classes call virtio_pci_force_virtio_1, but this doesn't happen until virtio_${subclass}_pci_release. So by the time we're able to report errors, virtio_pci_realize has already overwritten the user's disable_legacy setting, so we've lost the very piece of info we need to check to report errors with. Given the ordering of virtio_pci_realize vs the calls to virtio_pci_force_virtio_1 by subclasses, I don't see any option other than to use separate variables for the two distinct pieces of information. > > > > > Signed-off-by: Daniel P. Berrangé <berra...@redhat.com> > [...] > > diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h > > index bd223a6e3b..16ef4c0a3f 100644 > > --- a/hw/virtio/virtio-pci.h > > +++ b/hw/virtio/virtio-pci.h > > @@ -15,6 +15,7 @@ > > #ifndef QEMU_VIRTIO_PCI_H > > #define QEMU_VIRTIO_PCI_H > > > > +#include "qapi/error.h" > > #include "hw/pci/msi.h" > > #include "hw/virtio/virtio-bus.h" > > > > @@ -118,6 +119,12 @@ typedef struct VirtIOPCIQueue { > > uint32_t used[2]; > > } VirtIOPCIQueue; > > > > +typedef enum { > > + VIRTIO_PCI_MODE_LEGACY, > > + VIRTIO_PCI_MODE_TRANSITIONAL, > > + VIRTIO_PCI_MODE_MODERN, > > +} VirtIOPCIMode; > > + > > struct VirtIOPCIProxy { > > PCIDevice pci_dev; > > MemoryRegion bar; > > @@ -142,6 +149,7 @@ struct VirtIOPCIProxy { > > bool disable_modern; > > bool ignore_backend_features; > > OnOffAuto disable_legacy; > > + VirtIOPCIMode mode; > > uint32_t class_code; > > uint32_t nvectors; > > uint32_t dfselect; > > @@ -156,23 +164,34 @@ struct VirtIOPCIProxy { > > > > static inline bool virtio_pci_modern(VirtIOPCIProxy *proxy) > > { > > - return !proxy->disable_modern; > > + return proxy->mode != VIRTIO_PCI_MODE_LEGACY; > > } > > > > static inline bool virtio_pci_legacy(VirtIOPCIProxy *proxy) > > { > > - return proxy->disable_legacy == ON_OFF_AUTO_OFF; > > + return proxy->mode != VIRTIO_PCI_MODE_MODERN; > > } > > > > -static inline void virtio_pci_force_virtio_1(VirtIOPCIProxy *proxy) > > +static inline bool virtio_pci_force_virtio_1(VirtIOPCIProxy *proxy, > > + Error **errp) > > { > > - proxy->disable_modern = false; > > - proxy->disable_legacy = ON_OFF_AUTO_ON; > > + if (proxy->disable_legacy == ON_OFF_AUTO_OFF) { > > + error_setg(errp, "Unable to set disable-legacy=off on a virtio-1.0 > > " > > + "only device"); > > + return false; > > + } > > + if (proxy->disable_modern == true) { > > + error_setg(errp, "Unable to set disable-modern=on on a virtio-1.0 " > > + "only device"); > > + return false; > > + } > > + proxy->mode = VIRTIO_PCI_MODE_MODERN; > > + return true; > > } > > > > static inline void virtio_pci_disable_modern(VirtIOPCIProxy *proxy) > > { > > - proxy->disable_modern = true; > > + proxy->mode = VIRTIO_PCI_MODE_LEGACY; > > } > > > > /* > > -- > > 2.20.1 > > > > > > -- > Eduardo > Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|