5:50 a.m.
Unlike GPU assignment, mdev doesn't need the IOMMU to be enabled within kernel,
since the physical parent device takes care of the isolation, i.e. there's an
IOMMU group entry for each mdev created under sysfs, thus a VM can start
successfully
Erik Skultety (2):
util:mdev: Improve the error msg on non-existent mdev prior to VM
start
qemu: hostdev: Don't error out on domain with an mdev when IOMMU is
off
src/qemu/qemu_hostdev.c | 7 ++++++-
src/util/virmdev.c | 16 +++++++++++++---
2 files changed, 19 insertions(+), 4 deletions(-)
--
2.13.6
5:50 a.m.
New subject: [libvirt] [PATCH 1/2] util:mdev: Improve the error msg on non-existent mdev prior to VM start
What one currently gets is:
failed to read '/sys/bus/mdev/devices/<UUID>/mdev_type/device_api': No
such file or directory
This indicates that something is missing within the device's sysfs tree
which likely might be not be the case here because the device simply
doesn't exist yet. So, when creating our internal mdev obj, let's check
whether the device exists first prior to trying to verify the
user-provided model within domain XML.
Signed-off-by: Erik Skultety <eskultet(a)redhat.com>
---
src/util/virmdev.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/src/util/virmdev.c b/src/util/virmdev.c
index e4816cf20..2e3769aa6 100644
--- a/src/util/virmdev.c
+++ b/src/util/virmdev.c
@@ -150,13 +150,22 @@ virMediatedDeviceNew(const char *uuidstr, virMediatedDeviceModelType
model)
{
virMediatedDevicePtr ret = NULL;
virMediatedDevicePtr dev = NULL;
+ char *sysfspath = NULL;
+
+ if (!(sysfspath = virMediatedDeviceGetSysfsPath(uuidstr)))
+ goto cleanup;
+
+ if (!virFileExists(sysfspath)) {
+ virReportSystemError(errno, _("failed to read device '%s'"),
+ sysfspath);
+ goto cleanup;
+ }
if (VIR_ALLOC(dev) < 0)
- return NULL;
-
- if (!(dev->path = virMediatedDeviceGetSysfsPath(uuidstr)))
goto cleanup;
+ VIR_STEAL_PTR(dev->path, sysfspath);
+
/* Check whether the user-provided model corresponds with the actually
* supported mediated device's API.
*/
@@ -167,6 +176,7 @@ virMediatedDeviceNew(const char *uuidstr, virMediatedDeviceModelType
model)
VIR_STEAL_PTR(ret, dev);
cleanup:
+ VIR_FREE(sysfspath);
virMediatedDeviceFree(dev);
return ret;
}
--
2.13.6
6:08 a.m.
New subject: [libvirt] [PATCH 1/2] util:mdev: Improve the error msg on non-existent mdev prior to VM start
missing space in summary
On Fri, Mar 16, 2018 at 11:50:01 +0100, Erik Skultety wrote:
What one currently gets is:
failed to read '/sys/bus/mdev/devices/<UUID>/mdev_type/device_api': No
such file or directory
This indicates that something is missing within the device's sysfs tree
which likely might be not be the case here because the device simply
doesn't exist yet. So, when creating our internal mdev obj, let's check
whether the device exists first prior to trying to verify the
user-provided model within domain XML.
Signed-off-by: Erik Skultety <eskultet(a)redhat.com>
---
src/util/virmdev.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/src/util/virmdev.c b/src/util/virmdev.c
index e4816cf20..2e3769aa6 100644
--- a/src/util/virmdev.c
+++ b/src/util/virmdev.c
@@ -150,13 +150,22 @@ virMediatedDeviceNew(const char *uuidstr,
virMediatedDeviceModelType model)
{
virMediatedDevicePtr ret = NULL;
virMediatedDevicePtr dev = NULL;
+ char *sysfspath = NULL;
+
+ if (!(sysfspath = virMediatedDeviceGetSysfsPath(uuidstr)))
+ goto cleanup;
+
+ if (!virFileExists(sysfspath)) {
+ virReportSystemError(errno, _("failed to read device '%s'"),
+ sysfspath);
You did not try to read the device at this point. It merely does not
exist.
7:13 a.m.
New subject: [libvirt] [PATCH 1/2] util:mdev: Improve the error msg on non-existent mdev prior to VM start
On Fri, Mar 16, 2018 at 12:08:46PM +0100, Peter Krempa wrote:
missing space in summary
On Fri, Mar 16, 2018 at 11:50:01 +0100, Erik Skultety wrote:
> What one currently gets is:
> failed to read '/sys/bus/mdev/devices/<UUID>/mdev_type/device_api':
No
> such file or directory
>
> This indicates that something is missing within the device's sysfs tree
> which likely might be not be the case here because the device simply
> doesn't exist yet. So, when creating our internal mdev obj, let's check
> whether the device exists first prior to trying to verify the
> user-provided model within domain XML.
>
> Signed-off-by: Erik Skultety <eskultet(a)redhat.com>
> ---
> src/util/virmdev.c | 16 +++++++++++++---
> 1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/src/util/virmdev.c b/src/util/virmdev.c
> index e4816cf20..2e3769aa6 100644
> --- a/src/util/virmdev.c
> +++ b/src/util/virmdev.c
> @@ -150,13 +150,22 @@ virMediatedDeviceNew(const char *uuidstr,
virMediatedDeviceModelType model)
> {
> virMediatedDevicePtr ret = NULL;
> virMediatedDevicePtr dev = NULL;
> + char *sysfspath = NULL;
> +
> + if (!(sysfspath = virMediatedDeviceGetSysfsPath(uuidstr)))
> + goto cleanup;
> +
> + if (!virFileExists(sysfspath)) {
> + virReportSystemError(errno, _("failed to read device
'%s'"),
> + sysfspath);
You did not try to read the device at this point. It merely does not
exist.
Would you like "device '%s' not found" better?
Erik
7:15 a.m.
New subject: [libvirt] [PATCH 1/2] util:mdev: Improve the error msg on non-existent mdev prior to VM start
On Fri, Mar 16, 2018 at 13:13:41 +0100, Erik Skultety wrote:
On Fri, Mar 16, 2018 at 12:08:46PM +0100, Peter Krempa wrote:
> missing space in summary
>
> On Fri, Mar 16, 2018 at 11:50:01 +0100, Erik Skultety wrote:
> > What one currently gets is:
> > failed to read
'/sys/bus/mdev/devices/<UUID>/mdev_type/device_api': No
> > such file or directory
> >
> > This indicates that something is missing within the device's sysfs tree
> > which likely might be not be the case here because the device simply
> > doesn't exist yet. So, when creating our internal mdev obj, let's
check
> > whether the device exists first prior to trying to verify the
> > user-provided model within domain XML.
> >
> > Signed-off-by: Erik Skultety <eskultet(a)redhat.com>
> > ---
> > src/util/virmdev.c | 16 +++++++++++++---
> > 1 file changed, 13 insertions(+), 3 deletions(-)
> >
> > diff --git a/src/util/virmdev.c b/src/util/virmdev.c
> > index e4816cf20..2e3769aa6 100644
> > --- a/src/util/virmdev.c
> > +++ b/src/util/virmdev.c
> > @@ -150,13 +150,22 @@ virMediatedDeviceNew(const char *uuidstr,
virMediatedDeviceModelType model)
> > {
> > virMediatedDevicePtr ret = NULL;
> > virMediatedDevicePtr dev = NULL;
> > + char *sysfspath = NULL;
> > +
> > + if (!(sysfspath = virMediatedDeviceGetSysfsPath(uuidstr)))
> > + goto cleanup;
> > +
> > + if (!virFileExists(sysfspath)) {
> > + virReportSystemError(errno, _("failed to read device
'%s'"),
> > + sysfspath);
>
> You did not try to read the device at this point. It merely does not
> exist.
Would you like "device '%s' not found" better?
How about:
"mediated device '%s' not found", uuidstr ?
I don't think that adding the full sysfs path is any helpful since it's
generated from the uuid anyways.
5:50 a.m.
New subject: [libvirt] [PATCH 2/2] qemu: hostdev: Don't error out on domain with an mdev when IOMMU is off
Commit b4c2ac8d56 made a false assumption that IOMMU support necessary
for an mdev device to be assigned to a VM. Unlike direct PCI assignment,
IOMMU support is not needed for mediated devices, as the physical parent
device provides the IOMMU isolation, therefore, simply checking for VFIO
presence is enough to successfully start a VM.
Luckily, this issue is not very serious, since as of yet, libvirt
mandates the mdevs to be pre-created prior to a domain's launch, so this
patch will merely change the error the end user is going to see.
Previously:
unsupported configuration: Mediated host device assignment requires VFIO
support
Now:
failed to read device '/sys/bus/mdev/devices/<uuid>/': No such file or
directory
Signed-off-by: Erik Skultety <eskultet(a)redhat.com>
---
src/qemu/qemu_hostdev.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/src/qemu/qemu_hostdev.c b/src/qemu/qemu_hostdev.c
index 73d26f4c6..afe445d4e 100644
--- a/src/qemu/qemu_hostdev.c
+++ b/src/qemu/qemu_hostdev.c
@@ -330,9 +330,14 @@ qemuHostdevPrepareMediatedDevices(virQEMUDriverPtr driver,
int nhostdevs)
{
virHostdevManagerPtr hostdev_mgr = driver->hostdevMgr;
- bool supportsVFIO = qemuHostdevHostSupportsPassthroughVFIO();
+ bool supportsVFIO;
size_t i;
+ /* Checking for VFIO only is fine with mdev, as IOMMU isolation is achieved
+ * by the physical parent device.
+ */
+ supportsVFIO = virFileExists("/dev/vfio/vfio");
+
for (i = 0; i < nhostdevs; i++) {
if (hostdevs[i]->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS &&
hostdevs[i]->source.subsys.type == VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_MDEV) {
--
2.13.6
6:07 a.m.
New subject: [libvirt] [PATCH 2/2] qemu: hostdev: Don't error out on domain with an mdev when IOMMU is off
On Fri, Mar 16, 2018 at 11:50:02 +0100, Erik Skultety wrote:
Commit b4c2ac8d56 made a false assumption that IOMMU support
necessary
for an mdev device to be assigned to a VM. Unlike direct PCI assignment,
IOMMU support is not needed for mediated devices, as the physical parent
device provides the IOMMU isolation, therefore, simply checking for VFIO
presence is enough to successfully start a VM.
Luckily, this issue is not very serious, since as of yet, libvirt
mandates the mdevs to be pre-created prior to a domain's launch, so this
patch will merely change the error the end user is going to see.
Previously:
unsupported configuration: Mediated host device assignment requires VFIO
support
Now:
failed to read device '/sys/bus/mdev/devices/<uuid>/': No such file or
directory
I'm not sure I understood what you wanted to say in the commit message.
You are not requiring the IOMMU to bepresent for the mediated device
since isolation is inherent. This makes sense.
You are then giving an example of error message what would occur if the
iommu groups are not present on the host.
As a 'fixed' result you provide an error message if the user did not
create a MDEV prior to starting the VM. How is that relevant to this
patch? The VM should start just fine in that case, shouldn't it?
Signed-off-by: Erik Skultety <eskultet(a)redhat.com>
---
src/qemu/qemu_hostdev.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/src/qemu/qemu_hostdev.c b/src/qemu/qemu_hostdev.c
index 73d26f4c6..afe445d4e 100644
--- a/src/qemu/qemu_hostdev.c
+++ b/src/qemu/qemu_hostdev.c
@@ -330,9 +330,14 @@ qemuHostdevPrepareMediatedDevices(virQEMUDriverPtr driver,
int nhostdevs)
{
virHostdevManagerPtr hostdev_mgr = driver->hostdevMgr;
- bool supportsVFIO = qemuHostdevHostSupportsPassthroughVFIO();
+ bool supportsVFIO;
size_t i;
+ /* Checking for VFIO only is fine with mdev, as IOMMU isolation is achieved
+ * by the physical parent device.
+ */
+ supportsVFIO = virFileExists("/dev/vfio/vfio");
+
for (i = 0; i < nhostdevs; i++) {
if (hostdevs[i]->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS &&
hostdevs[i]->source.subsys.type == VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_MDEV)
{
--
2.13.6
--
libvir-list mailing list
libvir-list(a)redhat.com
https://www.redhat.com/mailman/listinfo/libvir-list
7:11 a.m.
New subject: [libvirt] [PATCH 2/2] qemu: hostdev: Don't error out on domain with an mdev when IOMMU is off
On Fri, Mar 16, 2018 at 12:07:50PM +0100, Peter Krempa wrote:
On Fri, Mar 16, 2018 at 11:50:02 +0100, Erik Skultety wrote:
> Commit b4c2ac8d56 made a false assumption that IOMMU support necessary
> for an mdev device to be assigned to a VM. Unlike direct PCI assignment,
> IOMMU support is not needed for mediated devices, as the physical parent
> device provides the IOMMU isolation, therefore, simply checking for VFIO
> presence is enough to successfully start a VM.
> Luckily, this issue is not very serious, since as of yet, libvirt
> mandates the mdevs to be pre-created prior to a domain's launch, so this
> patch will merely change the error the end user is going to see.
>
> Previously:
> unsupported configuration: Mediated host device assignment requires VFIO
> support
>
> Now:
> failed to read device '/sys/bus/mdev/devices/<uuid>/': No such file
or
> directory
I'm not sure I understood what you wanted to say in the commit message.
You are not requiring the IOMMU to bepresent for the mediated device
since isolation is inherent. This makes sense.
You are then giving an example of error message what would occur if the
iommu groups are not present on the host.
I should have been more clear about that. So, if you're referencing a
non-existent mdev within the domain XML, the error you get indicates something
that is not true, but you're right in what you deduced that you won't come
across this weird error if the device you're referencing already exists.
Therefore I mentioned in the patch that the issue isn't serious since
everything works if used correctly, only when you don't you'd experience some
odd messages, that's all, I'll rephrase the commit message.
Erik
2444
days inactive
2444
days old
7 comments
2 participants
participants (2)
-
Erik Skultety -
Peter Krempa