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vfio-pci: Allow mmap of MSIX BAR 

At the moment we unconditionally avoid mapping MSIX data of a BAR and
emulate MSIX table in QEMU. However it is 1) not always necessary as
a platform may provide a paravirt interface for MSIX configuration;
2) can affect the speed of MMIO access by emulating them in QEMU when
frequently accessed registers share same system page with MSIX data,
this is particularly a problem for systems with the page size bigger
than 4KB.

A new capability - VFIO_REGION_INFO_CAP_MSIX_MAPPABLE - has been added
to the kernel [1] which tells the userspace that mapping of the MSIX data
is possible now. This makes use of it so from now on QEMU tries mapping
the entire BAR as a whole and emulate MSIX on top of that.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a32295c612c57990d17fb0f41e7134394b2f35f6

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Alexey Kardashevskiy 2018-03-13 11:17:31 -06:00 committed by Alex Williamson
parent 567b5b309a
commit ae0215b2bb
3 changed files with 25 additions and 0 deletions
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15
hw/vfio/common.c
View File

@ -1471,6 +1471,21 @@ int vfio_get_dev_region_info(VFIODevice *vbasedev, uint32_t type,
return -ENODEV;
}
bool vfio_has_region_cap(VFIODevice *vbasedev, int region, uint16_t cap_type)
{
struct vfio_region_info *info = NULL;
bool ret = false;
if (!vfio_get_region_info(vbasedev, region, &info)) {
if (vfio_get_region_info_cap(info, cap_type)) {
ret = true;
}
g_free(info);
}
return ret;
}
/*
* Interfaces for IBM EEH (Enhanced Error Handling)
*/

9
hw/vfio/pci.c
View File

@ -1294,6 +1294,15 @@ static void vfio_pci_fixup_msix_region(VFIOPCIDevice *vdev)
off_t start, end;
VFIORegion *region = &vdev->bars[vdev->msix->table_bar].region;
/*
* If the host driver allows mapping of a MSIX data, we are going to
* do map the entire BAR and emulate MSIX table on top of that.
*/
if (vfio_has_region_cap(&vdev->vbasedev, region->nr,
VFIO_REGION_INFO_CAP_MSIX_MAPPABLE)) {
return;
}
/*
* We expect to find a single mmap covering the whole BAR, anything else
* means it's either unsupported or already setup.

1
include/hw/vfio/vfio-common.h
View File

@ -193,6 +193,7 @@ int vfio_get_region_info(VFIODevice *vbasedev, int index,
struct vfio_region_info **info);
int vfio_get_dev_region_info(VFIODevice *vbasedev, uint32_t type,
uint32_t subtype, struct vfio_region_info **info);
bool vfio_has_region_cap(VFIODevice *vbasedev, int region, uint16_t cap_type);
#endif
extern const MemoryListener vfio_prereg_listener;