Re: [libvirt] [PATCH 1/2] vfio/mdev: add version field as mandatory attribute for mdev device

On Tue, 23 Apr 2019 01:41:57 -0400 Yan Zhao <yan.y.zhao(a)intel.com&gt; wrote: > On Tue, Apr 23, 2019 at 09:21:00AM +0800, Alex Williamson wrote: > > On Mon, 22 Apr 2019 21:01:52 -0400 > > Yan Zhao <yan.y.zhao(a)intel.com&gt; wrote: > > > > > On Mon, Apr 22, 2019 at 10:39:50PM +0800, Alex Williamson wrote: > > > > On Fri, 19 Apr 2019 04:35:04 -0400 > > > > Yan Zhao <yan.y.zhao(a)intel.com&gt; wrote: > > > > > > > > > device version attribute in mdev sysfs is used by user space software > > > > > (e.g. libvirt) to query device compatibility for live migration of VFIO > > > > > mdev devices. This attribute is mandatory if a mdev device supports live > > > > > migration. > > > > > > > > The Subject: doesn't quite match what's being proposed here. > > > > > > > > > It consists of two parts: common part and vendor proprietary part. > > > > > common part: 32 bit. lower 16 bits is vendor id and higher 16 bits > > > > > identifies device type. e.g., for pci device, it is > > > > > "pci vendor id" | (VFIO_DEVICE_FLAGS_PCI << 16). > > > > > > > > What purpose does this serve? If it's intended as some sort of > > > > namespace feature, shouldn't we first assume that we can only support > > > > migration to devices of the same type? Therefore each type would > > > > already have its own namespace. Also that would make the trailing bit > > > > of the version string listed below in the example redundant. A vendor > > > > is still welcome to include this in their version string if they wish, > > > > but I think the string should be entirely vendor defined. > > > > > > > hi Alex, > > > This common part is a kind of namespace. > > > Because if version string is entirely defined by vendors, I'm worried about > > > if there is a case that one vendor's version string happens to deceive and > > > interfere with another vendor's version checking? > > > e.g. > > > vendor A has a version string like: vendor id + device id + mdev type > > > vendor B has a version string like: device id + vendor id + mdev type > > > but vendor A's vendor id is 0x8086, device id is 0x1217 > > > vendor B's vendor id is 0x1217, device id is 0x8086. > > > > > > In this corner case, the two vendors may regard the two device is > > > migratable but actually they are not. > > > > > > That's the reason for this common part that serve as a kind of namespace > > > that all vendors will comply with to avoid overlap. > > > > If we assume that migration can only occur between matching mdev types, > > this is redundant, each type already has their own namespace. > > > hi Alex, > do you mean user space software like libvirt needs to first check whether > mdev type is matching and then check whether version is matching? Yes.

> if user space software only checks version for migration, it means vendor > driver has to include mdev type in their vendor proprietary part string, > right? Userspace attempting to migrate an nvidia-64 to an i915-GVT_V5_4 would be a failure on the part of the user. > Another thing is that could there be any future mdev parent driver that > applies to all mdev devices, just like vfio-pci? like Yi's vfio-pci-mdev > driver (https://lkml.org/lkml/2019/3/13/114)? For starters, this is just a sample driver from which vendor specific mdev drivers could be forked to support these features, but additionally, the type is defined by the vendor driver, so even a meta driver like vfio-pci-mdev could create types like "vfio-pci-mdev-8086_10c9_abcdef" if it wanted to provide that specific device. The "vfio-pci-mdev-type1" is just a sample implementation to say "the native type of the thing bound to me" and it's going to have limited usefulness for any sort of persistence to userspace. Thus, it's a sample driver. Thanks,

> > > > > vendor proprietary part: this part is varied in length. vendor driver can > > > > > specify any string to identify a device. > > > > > > > > > > When reading this attribute, it should show device version string of the > > > > > device of type <type-id>. If a device does not support live migration, it > > > > > should return errno. > > > > > When writing a string to this attribute, it returns errno for > > > > > incompatibility or returns written string length in compatibility case. > > > > > If a device does not support live migration, it always returns errno. > > > > > > > > > > For user space software to use: > > > > > 1. > > > > > Before starting live migration, user space software first reads source side > > > > > mdev device's version. e.g. > > > > > "#cat \ > > > > > /sys/bus/pci/devices/0000\:00\:02.0/5ac1fb20-2bbf-4842-bb7e-36c58c3be9cd/mdev_type/version" > > > > > 00028086-193b-i915-GVTg_V5_4 > > > > > > > > > > 2. > > > > > Then, user space software writes the source side returned version string > > > > > to device version attribute in target side, and checks the return value. > > > > > If a negative errno is returned in the target side, then mdev devices in > > > > > source and target sides are not compatible; > > > > > If a positive number is returned and it equals to the length of written > > > > > string, then the two mdev devices in source and target side are compatible. > > > > > e.g. > > > > > (a) compatibility case > > > > > "# echo 00028086-193b-i915-GVTg_V5_4 > > > > > > /sys/bus/pci/devices/0000\:00\:02.0/882cc4da-dede-11e7-9180-078a62063ab1/mdev_type/version" > > > > > > > > > > (b) incompatibility case > > > > > "#echo 00028086-193b-i915-GVTg_V5_1 > > > > > > /sys/bus/pci/devices/0000\:00\:02.0/882cc4da-dede-11e7-9180-078a62063ab1/mdev_type/version" > > > > > -bash: echo: write error: Invalid argument > > > > > > > > > > 3. if two mdev devices are compatible, user space software can start > > > > > live migration, and vice versa. > > > > > > > > > > Note: if a mdev device does not support live migration, it either does > > > > > not provide a version attribute, or always returns errno when its version > > > > > attribute is read/written. > > > > > > > > I think it would be cleaner to do the former, not supply the > > > > attribute. This seems to do the latter in the sample drivers. Thanks, > > > Ok. you are right! > > > what about just keep one sample driver to show how to do the latter, > > > and let the others do the former? > > > > I'd rather that if a vendor driver doesn't support features requiring > > the version attribute that they don't implement it. It's confusing to > > developers looking at the sample driver for guidance if we have > > different implementations. Of course if you'd like to add migration > > support to one of the sample drivers, that'd be very welcome. Thanks, > > > Got it:) > > Thanks! > Yan > > > > > > > > Cc: Alex Williamson <alex.williamson(a)redhat.com&gt; > > > > > Cc: Erik Skultety <eskultet(a)redhat.com&gt; > > > > > Cc: "Dr. David Alan Gilbert" <dgilbert(a)redhat.com&gt; > > > > > Cc: Cornelia Huck <cohuck(a)redhat.com&gt; > > > > > Cc: "Tian, Kevin" <kevin.tian(a)intel.com&gt; > > > > > Cc: Zhenyu Wang <zhenyuw(a)linux.intel.com&gt; > > > > > Cc: "Wang, Zhi A" <zhi.a.wang(a)intel.com&gt; > > > > > Cc: Neo Jia <cjia(a)nvidia.com&gt; > > > > > Cc: Kirti Wankhede <kwankhede(a)nvidia.com&gt; > > > > > > > > > > Signed-off-by: Yan Zhao <yan.y.zhao(a)intel.com&gt; > > > > > --- > > > > > Documentation/vfio-mediated-device.txt | 36 ++++++++++++++++++++++++++ > > > > > samples/vfio-mdev/mbochs.c | 17 ++++++++++++ > > > > > samples/vfio-mdev/mdpy.c | 16 ++++++++++++ > > > > > samples/vfio-mdev/mtty.c | 16 ++++++++++++ > > > > > 4 files changed, 85 insertions(+) > > > > > > > > > > diff --git a/Documentation/vfio-mediated-device.txt b/Documentation/vfio-mediated-device.txt > > > > > index c3f69bcaf96e..bc28471c0667 100644 > > > > > --- a/Documentation/vfio-mediated-device.txt > > > > > +++ b/Documentation/vfio-mediated-device.txt > > > > > @@ -202,6 +202,7 @@ Directories and files under the sysfs for Each Physical Device > > > > > | | |--- available_instances > > > > > | | |--- device_api > > > > > | | |--- description > > > > > + | | |--- version > > > > > | | |--- [devices] > > > > > | |--- [<type-id>] > > > > > | | |--- create > > > > > @@ -209,6 +210,7 @@ Directories and files under the sysfs for Each Physical Device > > > > > | | |--- available_instances > > > > > | | |--- device_api > > > > > | | |--- description > > > > > + | | |--- version > > > > > | | |--- [devices] > > > > > | |--- [<type-id>] > > > > > | |--- create > > > > > @@ -216,6 +218,7 @@ Directories and files under the sysfs for Each Physical Device > > > > > | |--- available_instances > > > > > | |--- device_api > > > > > | |--- description > > > > > + | |--- version > > > > > | |--- [devices] > > > > > > > > > > * [mdev_supported_types] > > > > > @@ -225,6 +228,8 @@ Directories and files under the sysfs for Each Physical Device > > > > > [<type-id>], device_api, and available_instances are mandatory attributes > > > > > that should be provided by vendor driver. > > > > > > > > > > + version is a mandatory attribute if a mdev device supports live migration. > > > > > + > > > > > * [<type-id>] > > > > > > > > > > The [<type-id>] name is created by adding the device driver string as a prefix > > > > > @@ -246,6 +251,35 @@ Directories and files under the sysfs for Each Physical Device > > > > > This attribute should show the number of devices of type <type-id> that can be > > > > > created. > > > > > > > > > > +* version > > > > > + > > > > > + This attribute is rw. It is used to check whether two devices are compatible > > > > > + for live migration. If this attribute is missing, then the corresponding mdev > > > > > + device is regarded as not supporting live migration. > > > > > + > > > > > + It consists of two parts: common part and vendor proprietary part. > > > > > + common part: 32 bit. lower 16 bits is vendor id and higher 16 bits identifies > > > > > + device type. e.g., for pci device, it is > > > > > + "pci vendor id" | (VFIO_DEVICE_FLAGS_PCI << 16). > > > > > + vendor proprietary part: this part is varied in length. vendor driver can > > > > > + specify any string to identify a device. > > > > > + > > > > > + When reading this attribute, it should show device version string of the device > > > > > + of type <type-id>. If a device does not support live migration, it should > > > > > + return errno. > > > > > + When writing a string to this attribute, it returns errno for incompatibility > > > > > + or returns written string length in compatibility case. If a device does not > > > > > + support live migration, it always returns errno. > > > > > + > > > > > + for example. > > > > > + # cat \ > > > > > + /sys/bus/pci/devices/0000\:00\:02.0/mdev_supported_types/i915-GVTg_V5_2/version > > > > > + 00028086-193b-i915-GVTg_V5_2 > > > > > + > > > > > + #echo 00028086-193b-i915-GVTg_V5_2 > \ > > > > > + /sys/bus/pci/devices/0000\:00\:02.0/mdev_supported_types/i915-GVTg_V5_4/version > > > > > + -bash: echo: write error: Invalid argument > > > > > + > > > > > * [device] > > > > > > > > > > This directory contains links to the devices of type <type-id> that have been > > > > > @@ -327,12 +361,14 @@ card. > > > > > | | |-- available_instances > > > > > | | |-- create > > > > > | | |-- device_api > > > > > + | | |-- version > > > > > | | |-- devices > > > > > | | `-- name > > > > > | `-- mtty-2 > > > > > | |-- available_instances > > > > > | |-- create > > > > > | |-- device_api > > > > > + | |-- version > > > > > | |-- devices > > > > > | `-- name > > > > > |-- mtty_dev > > > > > diff --git a/samples/vfio-mdev/mbochs.c b/samples/vfio-mdev/mbochs.c > > > > > index b038aa9f5a70..2f5ba96b91a2 100644 > > > > > --- a/samples/vfio-mdev/mbochs.c > > > > > +++ b/samples/vfio-mdev/mbochs.c > > > > > @@ -1391,11 +1391,28 @@ static ssize_t device_api_show(struct kobject *kobj, struct device *dev, > > > > > } > > > > > MDEV_TYPE_ATTR_RO(device_api); > > > > > > > > > > +static ssize_t version_show(struct kobject *kobj, struct device *dev, > > > > > + char *buf) > > > > > +{ > > > > > + /* do not support live migration */ > > > > > + return -EINVAL; > > > > > +} > > > > > + > > > > > +static ssize_t version_store(struct kobject *kobj, struct device *dev, > > > > > + const char *buf, size_t count) > > > > > +{ > > > > > + /* do not support live migration */ > > > > > + return -EINVAL; > > > > > +} > > > > > + > > > > > +static MDEV_TYPE_ATTR_RW(version); > > > > > + > > > > > static struct attribute *mdev_types_attrs[] = { > > > > > &mdev_type_attr_name.attr, > > > > > &mdev_type_attr_description.attr, > > > > > &mdev_type_attr_device_api.attr, > > > > > &mdev_type_attr_available_instances.attr, > > > > > + &mdev_type_attr_version.attr, > > > > > NULL, > > > > > }; > > > > > > > > > > diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c > > > > > index cc86bf6566e4..ff15fdfc7d46 100644 > > > > > --- a/samples/vfio-mdev/mdpy.c > > > > > +++ b/samples/vfio-mdev/mdpy.c > > > > > @@ -695,11 +695,27 @@ static ssize_t device_api_show(struct kobject *kobj, struct device *dev, > > > > > } > > > > > MDEV_TYPE_ATTR_RO(device_api); > > > > > > > > > > +static ssize_t version_show(struct kobject *kobj, struct device *dev, > > > > > + char *buf) > > > > > +{ > > > > > + /* do not support live migration */ > > > > > + return -EINVAL; > > > > > +} > > > > > + > > > > > +static ssize_t version_store(struct kobject *kobj, struct device *dev, > > > > > + const char *buf, size_t count) > > > > > +{ > > > > > + /* do not support live migration */ > > > > > + return -EINVAL; > > > > > +} > > > > > +static MDEV_TYPE_ATTR_RW(version); > > > > > + > > > > > static struct attribute *mdev_types_attrs[] = { > > > > > &mdev_type_attr_name.attr, > > > > > &mdev_type_attr_description.attr, > > > > > &mdev_type_attr_device_api.attr, > > > > > &mdev_type_attr_available_instances.attr, > > > > > + &mdev_type_attr_version.attr, > > > > > NULL, > > > > > }; > > > > > > > > > > diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c > > > > > index 1c77c370c92f..4ae3aad3474d 100644 > > > > > --- a/samples/vfio-mdev/mtty.c > > > > > +++ b/samples/vfio-mdev/mtty.c > > > > > @@ -1390,10 +1390,26 @@ static ssize_t device_api_show(struct kobject *kobj, struct device *dev, > > > > > > > > > > MDEV_TYPE_ATTR_RO(device_api); > > > > > > > > > > +static ssize_t version_show(struct kobject *kobj, struct device *dev, > > > > > + char *buf) > > > > > +{ > > > > > + /* do not support live migration */ > > > > > + return -EINVAL; > > > > > +} > > > > > + > > > > > +static ssize_t version_store(struct kobject *kobj, struct device *dev, > > > > > + const char *buf, size_t count) > > > > > +{ > > > > > + /* do not support live migration */ > > > > > + return -EINVAL; > > > > > +} > > > > > + > > > > > +static MDEV_TYPE_ATTR_RW(version); > > > > > static struct attribute *mdev_types_attrs[] = { > > > > > &mdev_type_attr_name.attr, > > > > > &mdev_type_attr_device_api.attr, > > > > > &mdev_type_attr_available_instances.attr, > > > > > + &mdev_type_attr_version.attr, > > > > > NULL, > > > > > }; > > > > > > > > > > > > > _______________________________________________ > > > > intel-gvt-dev mailing list > > > > intel-gvt-dev(a)lists.freedesktop.org > > > > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev > > > > _______________________________________________ > > intel-gvt-dev mailing list > > intel-gvt-dev(a)lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev _______________________________________________ intel-gvt-dev mailing list intel-gvt-dev(a)lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev