| Message ID | 20250228152100.23105-1-frediano.ziglio@cloud.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | docs: Add some details on XenServer PCI devices | expand |
Hi, On Fri Feb 28, 2025 at 3:21 PM GMT, Frediano Ziglio wrote: > Describe the usage of devices 5853:0002 and 5853:C000. > > Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> > --- > docs/man/xen-pci-device-reservations.7.pod | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/docs/man/xen-pci-device-reservations.7.pod b/docs/man/xen-pci-device-reservations.7.pod > index 9ddf3a18ad..62f3bd2105 100644 > --- a/docs/man/xen-pci-device-reservations.7.pod > +++ b/docs/man/xen-pci-device-reservations.7.pod > @@ -10,6 +10,8 @@ use of this is with device ID 0x0001 to advertise the Xen Platform PCI > device - the presence of this virtual device enables a guest Operating > System (subject to the availability of suitable drivers) to make use of > paravirtualisation features such as disk and network devices etc. > +XenServer, for Windows machines, presents Xen Platform device with device > +ID 0x0002 instead of 0x0001. nit: in the interest of future-proofing the doc 's/presents/may present/'? > > Some Xen vendors wish to provide alternative and/or additional guest drivers > that can bind to virtual devices[1]. This may be done using the Xen PCI > @@ -86,4 +88,11 @@ and unplug protocol. > libxl provides support for creation of a single additional xen-pvdevice. > See the vendor_device parameter in xl.cfg(5). > > +=item 2. > + > +XenServer, for Windows machines, presents a device with ID 0xC000. > +This device is a placeholders for Windows update. > +Device 0xC000 is presented with a Xen Platform PCI device, usually with ID > +0x0002. > + > =back Wouldn't this be better covered under "=item 1"? Device 0xc000 is a xen-pvdevice, so it could be simplified to a single line of "XenServer uses device-id=0xc000 for its pvdevice on Windows guests", or something like that. Otherwise it reads as some other device, IMO. Cheers, Alejandro
On Tue, Mar 04, 2025 at 10:21:52AM +0000, Alejandro Vallejo wrote: > Hi, > > On Fri Feb 28, 2025 at 3:21 PM GMT, Frediano Ziglio wrote: > > Describe the usage of devices 5853:0002 and 5853:C000. > > > > Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> > > --- > > docs/man/xen-pci-device-reservations.7.pod | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/docs/man/xen-pci-device-reservations.7.pod b/docs/man/xen-pci-device-reservations.7.pod > > index 9ddf3a18ad..62f3bd2105 100644 > > --- a/docs/man/xen-pci-device-reservations.7.pod > > +++ b/docs/man/xen-pci-device-reservations.7.pod > > @@ -10,6 +10,8 @@ use of this is with device ID 0x0001 to advertise the Xen Platform PCI > > device - the presence of this virtual device enables a guest Operating > > System (subject to the availability of suitable drivers) to make use of > > paravirtualisation features such as disk and network devices etc. > > +XenServer, for Windows machines, presents Xen Platform device with device > > +ID 0x0002 instead of 0x0001. > > nit: in the interest of future-proofing the doc 's/presents/may present/'? > > > > > Some Xen vendors wish to provide alternative and/or additional guest drivers > > that can bind to virtual devices[1]. This may be done using the Xen PCI > > @@ -86,4 +88,11 @@ and unplug protocol. > > libxl provides support for creation of a single additional xen-pvdevice. > > See the vendor_device parameter in xl.cfg(5). > > > > +=item 2. > > + > > +XenServer, for Windows machines, presents a device with ID 0xC000. > > +This device is a placeholders for Windows update. > > +Device 0xC000 is presented with a Xen Platform PCI device, usually with ID > > +0x0002. > > + > > =back > > Wouldn't this be better covered under "=item 1"? Device 0xc000 is a > xen-pvdevice, so it could be simplified to a single line of "XenServer uses > device-id=0xc000 for its pvdevice on Windows guests", or something like that. I think it's important to note that c000 always appears in conjunction with 0001 or 0002, and it's not a replacement for either of those devices. Likewise it's important to note that 0001 and 0002 are to my understanding mutually exclusive, and only one of those must be exposed. Thanks, Roger.
On Tue, Mar 4, 2025 at 11:08 AM Roger Pau Monné <roger.pau@citrix.com> wrote: > > On Tue, Mar 04, 2025 at 10:21:52AM +0000, Alejandro Vallejo wrote: > > Hi, > > > > On Fri Feb 28, 2025 at 3:21 PM GMT, Frediano Ziglio wrote: > > > Describe the usage of devices 5853:0002 and 5853:C000. > > > > > > Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> > > > --- > > > docs/man/xen-pci-device-reservations.7.pod | 9 +++++++++ > > > 1 file changed, 9 insertions(+) > > > > > > diff --git a/docs/man/xen-pci-device-reservations.7.pod b/docs/man/xen-pci-device-reservations.7.pod > > > index 9ddf3a18ad..62f3bd2105 100644 > > > --- a/docs/man/xen-pci-device-reservations.7.pod > > > +++ b/docs/man/xen-pci-device-reservations.7.pod > > > @@ -10,6 +10,8 @@ use of this is with device ID 0x0001 to advertise the Xen Platform PCI > > > device - the presence of this virtual device enables a guest Operating > > > System (subject to the availability of suitable drivers) to make use of > > > paravirtualisation features such as disk and network devices etc. > > > +XenServer, for Windows machines, presents Xen Platform device with device > > > +ID 0x0002 instead of 0x0001. > > > > nit: in the interest of future-proofing the doc 's/presents/may present/'? > > > > > > > > Some Xen vendors wish to provide alternative and/or additional guest drivers > > > that can bind to virtual devices[1]. This may be done using the Xen PCI > > > @@ -86,4 +88,11 @@ and unplug protocol. > > > libxl provides support for creation of a single additional xen-pvdevice. > > > See the vendor_device parameter in xl.cfg(5). > > > > > > +=item 2. > > > + > > > +XenServer, for Windows machines, presents a device with ID 0xC000. > > > +This device is a placeholders for Windows update. > > > +Device 0xC000 is presented with a Xen Platform PCI device, usually with ID > > > +0x0002. > > > + > > > =back > > > > Wouldn't this be better covered under "=item 1"? Device 0xc000 is a > > xen-pvdevice, so it could be simplified to a single line of "XenServer uses > > device-id=0xc000 for its pvdevice on Windows guests", or something like that. > > I think it's important to note that c000 always appears in conjunction > with 0001 or 0002, and it's not a replacement for either of those > devices. > Do you have something more precise in mind? Can you suggest what to write? > Likewise it's important to note that 0001 and 0002 are to my > understanding mutually exclusive, and only one of those must be > exposed. Not exactly sure if this is a must or a should. From my testing, presenting 2 devices (well, they are mostly the same) works. But, as they do the same things it seems reasonable to avoid the duplication. It looks like a good recommendation. > > Thanks, Roger. Frediano
On Tue, Mar 04, 2025 at 11:17:42AM +0000, Frediano Ziglio wrote: > On Tue, Mar 4, 2025 at 11:08 AM Roger Pau Monné <roger.pau@citrix.com> wrote: > > > > On Tue, Mar 04, 2025 at 10:21:52AM +0000, Alejandro Vallejo wrote: > > > Hi, > > > > > > On Fri Feb 28, 2025 at 3:21 PM GMT, Frediano Ziglio wrote: > > > > Describe the usage of devices 5853:0002 and 5853:C000. > > > > > > > > Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> > > > > --- > > > > docs/man/xen-pci-device-reservations.7.pod | 9 +++++++++ > > > > 1 file changed, 9 insertions(+) > > > > > > > > diff --git a/docs/man/xen-pci-device-reservations.7.pod b/docs/man/xen-pci-device-reservations.7.pod > > > > index 9ddf3a18ad..62f3bd2105 100644 > > > > --- a/docs/man/xen-pci-device-reservations.7.pod > > > > +++ b/docs/man/xen-pci-device-reservations.7.pod > > > > @@ -10,6 +10,8 @@ use of this is with device ID 0x0001 to advertise the Xen Platform PCI > > > > device - the presence of this virtual device enables a guest Operating > > > > System (subject to the availability of suitable drivers) to make use of > > > > paravirtualisation features such as disk and network devices etc. > > > > +XenServer, for Windows machines, presents Xen Platform device with device > > > > +ID 0x0002 instead of 0x0001. > > > > > > nit: in the interest of future-proofing the doc 's/presents/may present/'? > > > > > > > > > > > Some Xen vendors wish to provide alternative and/or additional guest drivers > > > > that can bind to virtual devices[1]. This may be done using the Xen PCI > > > > @@ -86,4 +88,11 @@ and unplug protocol. > > > > libxl provides support for creation of a single additional xen-pvdevice. > > > > See the vendor_device parameter in xl.cfg(5). > > > > > > > > +=item 2. > > > > + > > > > +XenServer, for Windows machines, presents a device with ID 0xC000. > > > > +This device is a placeholders for Windows update. > > > > +Device 0xC000 is presented with a Xen Platform PCI device, usually with ID > > > > +0x0002. > > > > + > > > > =back > > > > > > Wouldn't this be better covered under "=item 1"? Device 0xc000 is a > > > xen-pvdevice, so it could be simplified to a single line of "XenServer uses > > > device-id=0xc000 for its pvdevice on Windows guests", or something like that. > > > > I think it's important to note that c000 always appears in conjunction > > with 0001 or 0002, and it's not a replacement for either of those > > devices. > > > > Do you have something more precise in mind? Can you suggest what to write? I'm fine with your proposed text, my reply was to Alejandro to note that I think his proposed text was missing information that was on your original proposal. "XenServer might present a device with ID 0xC000. Such device is a placeholder for Windows update usage and is always exposed in conjunction with a Xen Platform PCI device, usually with ID 0x0002." I don't care much whether this is on a separate item or not. My preference would be for adding a second item, as to prevent cluttering the first one. I've also looked at xl.cfg, and it mentions: vendor_device="VENDOR_DEVICE" Selects which variant of the QEMU xen-pvdevice should be used for this guest. Valid values are: none The xen-pvdevice should be omitted. This is the default. xenserver The xenserver variant of the xen-pvdevice (device-id=C000) will be specified, enabling the use of XenServer PV drivers in the guest. Isn't this wrong, as selecting `xenserver` should instead use device-id=0002 but not C000? Maybe I'm not understanding how this is supported to work. > > Likewise it's important to note that 0001 and 0002 are to my > > understanding mutually exclusive, and only one of those must be > > exposed. > > Not exactly sure if this is a must or a should. From my testing, > presenting 2 devices (well, they are mostly the same) works. But, as > they do the same things it seems reasonable to avoid the duplication. > It looks like a good recommendation. I was expecting it to not work, as I imagined Linux would then attempt to initialize the grant tables twice for example. Thanks, Roger.
On Tue, Mar 4, 2025 at 12:30 PM Roger Pau Monné <roger.pau@citrix.com> wrote: > > On Tue, Mar 04, 2025 at 11:17:42AM +0000, Frediano Ziglio wrote: > > On Tue, Mar 4, 2025 at 11:08 AM Roger Pau Monné <roger.pau@citrix.com> wrote: > > > > > > On Tue, Mar 04, 2025 at 10:21:52AM +0000, Alejandro Vallejo wrote: > > > > Hi, > > > > > > > > On Fri Feb 28, 2025 at 3:21 PM GMT, Frediano Ziglio wrote: > > > > > Describe the usage of devices 5853:0002 and 5853:C000. > > > > > > > > > > Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> > > > > > --- > > > > > docs/man/xen-pci-device-reservations.7.pod | 9 +++++++++ > > > > > 1 file changed, 9 insertions(+) > > > > > > > > > > diff --git a/docs/man/xen-pci-device-reservations.7.pod b/docs/man/xen-pci-device-reservations.7.pod > > > > > index 9ddf3a18ad..62f3bd2105 100644 > > > > > --- a/docs/man/xen-pci-device-reservations.7.pod > > > > > +++ b/docs/man/xen-pci-device-reservations.7.pod > > > > > @@ -10,6 +10,8 @@ use of this is with device ID 0x0001 to advertise the Xen Platform PCI > > > > > device - the presence of this virtual device enables a guest Operating > > > > > System (subject to the availability of suitable drivers) to make use of > > > > > paravirtualisation features such as disk and network devices etc. > > > > > +XenServer, for Windows machines, presents Xen Platform device with device > > > > > +ID 0x0002 instead of 0x0001. > > > > > > > > nit: in the interest of future-proofing the doc 's/presents/may present/'? > > > > > > > > > > > > > > Some Xen vendors wish to provide alternative and/or additional guest drivers > > > > > that can bind to virtual devices[1]. This may be done using the Xen PCI > > > > > @@ -86,4 +88,11 @@ and unplug protocol. > > > > > libxl provides support for creation of a single additional xen-pvdevice. > > > > > See the vendor_device parameter in xl.cfg(5). > > > > > > > > > > +=item 2. > > > > > + > > > > > +XenServer, for Windows machines, presents a device with ID 0xC000. > > > > > +This device is a placeholders for Windows update. > > > > > +Device 0xC000 is presented with a Xen Platform PCI device, usually with ID > > > > > +0x0002. > > > > > + > > > > > =back > > > > > > > > Wouldn't this be better covered under "=item 1"? Device 0xc000 is a > > > > xen-pvdevice, so it could be simplified to a single line of "XenServer uses > > > > device-id=0xc000 for its pvdevice on Windows guests", or something like that. > > > > > > I think it's important to note that c000 always appears in conjunction > > > with 0001 or 0002, and it's not a replacement for either of those > > > devices. > > > > > > > Do you have something more precise in mind? Can you suggest what to write? > > I'm fine with your proposed text, my reply was to Alejandro to note > that I think his proposed text was missing information that was on > your original proposal. > > "XenServer might present a device with ID 0xC000. Such device is a > placeholder for Windows update usage and is always exposed in > conjunction with a Xen Platform PCI device, usually with ID 0x0002." > > I don't care much whether this is on a separate item or not. My > preference would be for adding a second item, as to prevent cluttering > the first one. > > I've also looked at xl.cfg, and it mentions: > > vendor_device="VENDOR_DEVICE" > > Selects which variant of the QEMU xen-pvdevice should be used for this > guest. Valid values are: > > none The xen-pvdevice should be omitted. This is the default. > > xenserver The xenserver variant of the xen-pvdevice (device-id=C000) > will be specified, enabling the use of XenServer PV drivers in the > guest. > > Isn't this wrong, as selecting `xenserver` should instead use > device-id=0002 but not C000? Maybe I'm not understanding how this is > supported to work. > No, the device is correct, it should be C000. 0002 is a xen platform device, C000 is a xen-pvdevice device. Apparently device 0002 was the first attempt to make Windows update pick up Citrix drivers on Windows, C000 is the final attempt. Note that recently released XCP-ng signed drivers are supporting both devices 0001 and 0002 (I hope this sentence does not cause more questions than answers). > > > Likewise it's important to note that 0001 and 0002 are to my > > > understanding mutually exclusive, and only one of those must be > > > exposed. > > > > Not exactly sure if this is a must or a should. From my testing, > > presenting 2 devices (well, they are mostly the same) works. But, as > > they do the same things it seems reasonable to avoid the duplication. > > It looks like a good recommendation. > > I was expecting it to not work, as I imagined Linux would then attempt > to initialize the grant tables twice for example. > That's the reason why not to present 2 of these devices. But one would override the other and everything should work even on Linux. > Thanks, Roger. Preparing a v2. Frediano
For the record, my remarks are fairly inconsequential. This patch is a net positive addition to the man page and I think it should go in. On Tue Mar 4, 2025 at 12:29 PM GMT, Roger Pau Monné wrote: > On Tue, Mar 04, 2025 at 11:17:42AM +0000, Frediano Ziglio wrote: > > On Tue, Mar 4, 2025 at 11:08 AM Roger Pau Monné <roger.pau@citrix.com> wrote: > > > > > > On Tue, Mar 04, 2025 at 10:21:52AM +0000, Alejandro Vallejo wrote: > > > > Hi, > > > > > > > > On Fri Feb 28, 2025 at 3:21 PM GMT, Frediano Ziglio wrote: > > > > > Describe the usage of devices 5853:0002 and 5853:C000. > > > > > > > > > > Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> > > > > > --- > > > > > docs/man/xen-pci-device-reservations.7.pod | 9 +++++++++ > > > > > 1 file changed, 9 insertions(+) > > > > > > > > > > diff --git a/docs/man/xen-pci-device-reservations.7.pod b/docs/man/xen-pci-device-reservations.7.pod > > > > > index 9ddf3a18ad..62f3bd2105 100644 > > > > > --- a/docs/man/xen-pci-device-reservations.7.pod > > > > > +++ b/docs/man/xen-pci-device-reservations.7.pod > > > > > @@ -10,6 +10,8 @@ use of this is with device ID 0x0001 to advertise the Xen Platform PCI > > > > > device - the presence of this virtual device enables a guest Operating > > > > > System (subject to the availability of suitable drivers) to make use of > > > > > paravirtualisation features such as disk and network devices etc. > > > > > +XenServer, for Windows machines, presents Xen Platform device with device > > > > > +ID 0x0002 instead of 0x0001. > > > > > > > > nit: in the interest of future-proofing the doc 's/presents/may present/'? > > > > > > > > > > > > > > Some Xen vendors wish to provide alternative and/or additional guest drivers > > > > > that can bind to virtual devices[1]. This may be done using the Xen PCI > > > > > @@ -86,4 +88,11 @@ and unplug protocol. > > > > > libxl provides support for creation of a single additional xen-pvdevice. > > > > > See the vendor_device parameter in xl.cfg(5). > > > > > > > > > > +=item 2. > > > > > + > > > > > +XenServer, for Windows machines, presents a device with ID 0xC000. > > > > > +This device is a placeholders for Windows update. > > > > > +Device 0xC000 is presented with a Xen Platform PCI device, usually with ID > > > > > +0x0002. > > > > > + > > > > > =back > > > > > > > > Wouldn't this be better covered under "=item 1"? Device 0xc000 is a > > > > xen-pvdevice, so it could be simplified to a single line of "XenServer uses > > > > device-id=0xc000 for its pvdevice on Windows guests", or something like that. > > > > > > I think it's important to note that c000 always appears in conjunction > > > with 0001 or 0002, and it's not a replacement for either of those > > > devices. That's already stated in the item1 description. Note that the presence of the Xen Platform PCI device is generally a pre-requisite for an additional xen-pvdevice as it is the platform device that provides that IO ports necessary for unplugging emulated devices. See hvm-emulated-unplug.markdown for details of the IO ports and unplug protocol. > > > > > > > Do you have something more precise in mind? Can you suggest what to write? > > I'm fine with your proposed text, my reply was to Alejandro to note > that I think his proposed text was missing information that was on > your original proposal. > > "XenServer might present a device with ID 0xC000. Such device is a > placeholder for Windows update usage and is always exposed in > conjunction with a Xen Platform PCI device, usually with ID 0x0002." > > I don't care much whether this is on a separate item or not. My > preference would be for adding a second item, as to prevent cluttering > the first one. > > I've also looked at xl.cfg, and it mentions: > > vendor_device="VENDOR_DEVICE" > > Selects which variant of the QEMU xen-pvdevice should be used for this > guest. Valid values are: > > none The xen-pvdevice should be omitted. This is the default. > > xenserver The xenserver variant of the xen-pvdevice (device-id=C000) > will be specified, enabling the use of XenServer PV drivers in the > guest. > > Isn't this wrong, as selecting `xenserver` should instead use > device-id=0002 but not C000? Maybe I'm not understanding how this is > supported to work. I think there's some confusion going on. xen-pvdevice != xen-platformdevice pvdevice is 0xc000. platformdevice is 0001 or 0002. platformdevice is the PCI device used for device unplug, grant table initialization and so on. pvdevice is a true dummy device present for the sole purpose of letting Windows bind the drivers to an actual device that can't be 0002 for (afaiui) very, very, very stupid and non-technical reasons. The man page HINTS at this when talking about binding drivers to devices. > > > > Likewise it's important to note that 0001 and 0002 are to my > > > understanding mutually exclusive, and only one of those must be > > > exposed. > > > > Not exactly sure if this is a must or a should. From my testing, > > presenting 2 devices (well, they are mostly the same) works. But, as > > they do the same things it seems reasonable to avoid the duplication. > > It looks like a good recommendation. > > I was expecting it to not work, as I imagined Linux would then attempt > to initialize the grant tables twice for example. > > Thanks, Roger. It may very well be a case of "happens to work, but it really shouldn't". The code does go through `gnttab_init()` twice if the probe succeeds twice. Not that it couldn't be changed to behave differently, but it currently doesn't. Anyhow, I think you're right in that 0001 and 0002 must not coexist even if mechanically they may be able to. In the name of everyone's sanity. Cheers, Alejandro
diff --git a/docs/man/xen-pci-device-reservations.7.pod b/docs/man/xen-pci-device-reservations.7.pod index 9ddf3a18ad..62f3bd2105 100644 --- a/docs/man/xen-pci-device-reservations.7.pod +++ b/docs/man/xen-pci-device-reservations.7.pod @@ -10,6 +10,8 @@ use of this is with device ID 0x0001 to advertise the Xen Platform PCI device - the presence of this virtual device enables a guest Operating System (subject to the availability of suitable drivers) to make use of paravirtualisation features such as disk and network devices etc. +XenServer, for Windows machines, presents Xen Platform device with device +ID 0x0002 instead of 0x0001. Some Xen vendors wish to provide alternative and/or additional guest drivers that can bind to virtual devices[1]. This may be done using the Xen PCI @@ -86,4 +88,11 @@ and unplug protocol. libxl provides support for creation of a single additional xen-pvdevice. See the vendor_device parameter in xl.cfg(5). +=item 2. + +XenServer, for Windows machines, presents a device with ID 0xC000. +This device is a placeholders for Windows update. +Device 0xC000 is presented with a Xen Platform PCI device, usually with ID +0x0002. + =back
Describe the usage of devices 5853:0002 and 5853:C000. Signed-off-by: Frediano Ziglio <frediano.ziglio@cloud.com> --- docs/man/xen-pci-device-reservations.7.pod | 9 +++++++++ 1 file changed, 9 insertions(+)