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Subject: Re: [PATCH v2 4/4] Add support for MSI-X vectors configuration for PCI VFs
å 2022/1/24 äå5:39, Max Gurtovoy åé:
A typical cloud provider SR-IOV use case is to create many VFs for
use by guest VMs. The VFs may not be assigned to a VM until a user
requests a VM of a certain size, e.g., number of CPUs. A VF may need
MSI-X vectors proportional to the number of CPUs in the VM, but there is
no standard way today in the spec to change the number of MSI-X vectors
supported by a VF, although there are some operating systems that
support this.
Introduce new admin commands for a generic interrupt vector management
for PCI VFs. For now, this mechanism will manage the MSI-X interrupt
vectors assignments of a VF by its parent PF.
These admin commands will be easily extended, if needed, for other types
of interrupt vectors in the future with backward compatibility to old
drivers and devices.
Reviewed-by: Parav Pandit <parav@nvidia.com>
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
---
admin-virtq.tex | 150 +++++++++++++++++++++++++++++++++++++++++++++++-
content.tex | 44 ++++++++++++++
2 files changed, 192 insertions(+), 2 deletions(-)
diff --git a/admin-virtq.tex b/admin-virtq.tex
index 1a41c22..b57b57d 100644
--- a/admin-virtq.tex
+++ b/admin-virtq.tex
@@ -64,7 +64,13 @@ \section{Admin Virtqueues}\label{sec:Basic Facilities of a Virtio Device / Admin
\hline \hline
0000h & VIRTIO_ADMIN_CAPS_IDENTIFY & M \\
\hline
-0001h - 7FFFh & Generic admin cmds & - \\
+0001h & VIRTIO_ADMIN_PCI_SRIOV_ATTRS & O \\
+\hline
+0002h & VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_SET & O \\
+\hline
+0003h & VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_GET & O \\
+\hline
+0004h - 7FFFh & Generic admin cmds & - \\
\hline
8000h - FFFFh & Reserved & - \\
\hline
@@ -78,7 +84,8 @@ \subsection{VIRTIO ADMIN CAPS IDENTIFY command}\label{sec:Basic Facilities of a
\begin{lstlisting}
struct virtio_admin_caps_identify_result {
/*
- * caps[0] - Bit 0x0 - Bit 0x7 are reserved
+ * caps[0] - Bit 0x0 - if set, VF MSI-X control supported
+ * Bit 0x1 - Bit 0x7 are reserved
* caps[1] - Bit 0x0 - Bit 0x7 are reserved
* caps[2] - Bit 0x0 - Bit 0x7 are reserved
* ....
@@ -87,3 +94,142 @@ \subsection{VIRTIO ADMIN CAPS IDENTIFY command}\label{sec:Basic Facilities of a
u8 caps[8192];
};
\end{lstlisting}
+
+For more details on VF MSI-X configuration support see section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Admin command set / VF MSI-X control}.
+
+\subsection{VIRTIO ADMIN PCI SRIOV ATTRS command}\label{sec:Basic Facilities of a Virtio Device / Admin Virtqueues / VIRTIO ADMIN PCI SRIOV ATTRS command}
+
So this is all for PCI transport, do we need to 1) move this to PCI transport or 2) use non PCI specific termiology (PF/VF) here ?
+The VIRTIO_ADMIN_PCI_SRIOV_ATTRS command has no command specific data set by the driver.
+This command upon success, returns a data buffer that describes information about PCI SRIOV
+related capabilities and attributes for the device. This command can be supported only by
+PCI devices that supports Single Root I/O Virtualization.
+This information is of form:
+\begin{lstlisting}
+struct virtio_admin_pci_sriov_attrs_result {
+ /* For compatibility - indicates which of the below fields are valid (1 means valid):
+ * Bit 0x0 - vfs_free_msix_count
+ * Bit 0x1 - per_vf_max_msix_count
+ * Bits 0x2 - 0x3F - reserved for future fields
+ */
So we have several layers of compatibilities: 1) feature bits 2) cap bitmap / identifiy3) attrs_mask (no negotiation so it's unclear that how the compatibility can work here).
This looks like a burden for the management.Is it really helpful to have a device that can only return free_msix_count but not per_vf_max_msix_count?
And I think it's better to explicit split the commands then we can have dedicated commands for MSI instead of trying to mix all SRIOV related attributes into the same command.
+ le64 attrs_mask;
+ /* Number of free msix vectors in the global msix pool for VFs */
+ le32 vfs_free_msix_count;
+ /* Max number of msix vectors that can be assigned for a single VF */
+ le16 per_vf_max_msix_count;
+};
+\end{lstlisting}
+
+\subsection{VIRTIO ADMIN PCI VF INTERRUPT CONFIG SET command}\label{sec:Basic Facilities of a Virtio Device / Admin Virtqueues / VIRTIO ADMIN PCI VF INTERRUPT CONFIG SET command}
+
+The VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_SET command is used to modify the interrupt vectors
+count for a PCI virtual function. The command specific data set by the driver is of form:
+\begin{lstlisting}
+struct virtio_admin_pci_vf_interrupt_config_set_data {
+ /* The virtual function number */
+ le16 vf_number;
+ /* For compatibility - indicates which of the below properties should be
+ * modified (1 means that field should be modified):
+ * Bit 0x0 - msix_count
+ * Bits 0x1 - 0x3F - reserved for future fields
+ */
+ le64 attrs_mask;
+ /* The amount of MSI-X interrupt vectors */
+ le16 msix_count;
+};
+\end{lstlisting}
I think it's better to have a dedicated command to set the msix_vectors, then there's no need for the attrs_mask.
+
+The following table describes the command specific error codes codes:
+
+\begin{tabular}{|l|l|l|}
+\hline
+Opcode & Status & Description \\
+\hline \hline
+00h & VIRTIO_ADMIN_CS_ERR_PCI_VF_NUM_INVALID & invalid VF number \\
Does it mean it exceeds the totalVFs? We need an accurate definition on "invalid" here.
+\hline +01h & VIRTIO_ADMIN_CS_ERR_PCI_MSIX_COUNT_EXCEED & MSI-X count exceed the max value per VF \\
I guess it's actually per_vf_max_msix_count? What if the device doesn't give us per_vf_max_msix_count (it's odd but it's allowed in this propsal if I was not wrong).
+\hline +02h & VIRTIO_ADMIN_CS_ERR_PCI_MSIX_POOL_NO_RSC & MSI-X count exceed the free pool resources \\ +\hline
Do we need to define "pool" here?
+03h & VIRTIO_ADMIN_CS_ERR_PCI_VF_IN_USE & VF is already in use, operation failed \\
How do you define "VF is already in use"? Is this command only applicable when sriov_numvfs in the capability is zero? How about the initial associated VF via initial_vfs?
+\hline
+04h - FFh & Reserved & - \\
+\hline
+\end{tabular}
+
+\begin{note}
+{vf_number can't be greater than NumVFs value as defined in the PCI specification
+or smaller than 1. A command specific error status code VIRTIO_ADMIN_CS_ERR_PCI_VF_NUM_INVALID
+is returned when vf_number is out of the range.}
Should be TotalVFs in the SR-IOV extended capability.
+\end{note}
+
+\begin{note}
+{A command specific error status code VIRTIO_ADMIN_CS_ERR_PCI_MSIX_COUNT_EXCEED
+is returned when the amount of MSI-X to assign exceed the maximum value that can be
+assigned to a single VF.}
+\end{note}
+
+\begin{note}
+{A command specific error status code VIRTIO_ADMIN_CS_ERR_PCI_MSIX_POOL_NO_RSC
+is returned when the amount of MSI-X to assign exceed the amount of free MSI-X
+vectors in the global pool.}
+\end{note}
+
+This command has no command specific result set by the device. Upon success, the device guarantees
+that all the requested properties were modified to the given values. Otherwise, error will be returned.
+
+\begin{note}
+{Before setting msix_count property the virtual/managed device (VF) shall be un-initialized and may not be used by the driver.
+Otherwise, a command specific error status code VIRTIO_ADMIN_CS_ERR_PCI_VF_IN_USE will be returned.}
How did the device know whether or not VF is not used by any driver?
+\end{note}
+
+\subsection{VIRTIO ADMIN PCI VF INTERRUPT CONFIG GET command}\label{sec:Basic Facilities of a Virtio Device / Admin Virtqueues / VIRTIO ADMIN PCI VF INTERRUPT CONFIG GET command}
+
+The VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_GET command is used to obtain the values of the VFs
+interrupt vectors configuration.
+The command specific data set by the driver is of form:
+\begin{lstlisting}
+struct virtio_admin_pci_vf_interrupt_config_get_data {
+ /* The virtual function number */
+ le16 vf_number;
+ /* For compatibility - indicates which of the below properties should be
+ * queried (1 means that field should be queried):
+ * Bit 0x0 - msix_count (The amount of MSI-X interrupt vectors)
+ * Bits 0x1 - 0x3F - reserved for future fields
+ */
+ le64 attrs_mask;
+};
+\end{lstlisting}
+
+The following table describes the command specific error codes codes:
+
+\begin{tabular}{|l|l|l|}
+\hline
+Opcode & Status & Description \\
+\hline \hline
+00h & VIRTIO_ADMIN_CS_ERR_PCI_VF_NUM_INVALID & invalid VF number \\
+\hline
+01h - FFh & Reserved & - \\
+\hline
+\end{tabular}
+
+\begin{note}
+{vf_number can't be greater than NumVFs value as defined in the PCI specification
I guess for NumVFs you meant the TotalVFs in SR-IOV extended capability.
+or smaller than 1. A command specific error status code VIRTIO_ADMIN_CS_ERR_PCI_VF_NUM_INVALID +is returned when vf_number is out of the range.} +\end{note} + +This command, upon success, returns a data buffer that describes the properties that were requested +and their values for the subject virtio VF device according to the given vf_number. +This information is of form: +\begin{lstlisting} +struct virtio_admin_pci_vf_interrupt_config_get_result { + /* For compatibility - indicates which of the below fields were returned + * (1 means that field was returned): + * Bit 0x0 - msix_count + * Bits 0x1 - 0x3F - reserved for future fields + */ + le64 attrs_mask; + /* The amount of MSI-X interrupt vectors currently assigned to the VF */ + le16 msix_count; +}; +\end{lstlisting} diff --git a/content.tex b/content.tex index 18a5c66..2dd1d46 100644 --- a/content.tex +++ b/content.tex @@ -1734,6 +1734,50 @@ \subsubsection{Driver Handling Interrupts}\label{sec:Virtio Transport Options / \end{itemize} \end{itemize}+\subsection{PCI-specific Admin capabilities}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Admin capabilities}+ +This documents the group of Admin capabilities for PCI virtio devices. Each capability is +implemented using one or more Admin queue commands. + +\subsubsection{VF MSI-X control}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Admin command set / VF MSI-X control} + +This capability enables a virtio PCI PF device to control the assignment of MSI-X interrupt vectors +for its managed VFs. Capable devices will need to set bit 0x0 of caps[0] in the result of VIRTIO_ADMIN_CAPS_IDENTIFY +admin command. See section \ref{sec:Basic Facilities of a Virtio Device / Admin Virtqueues / VIRTIO ADMIN CAPS IDENTIFY command} +for more details. + +Capable devices will also need to implement VIRTIO_ADMIN_PCI_SRIOV_ATTRS, VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_SET and +VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_GET admin commands. + +In the result of VIRTIO_ADMIN_PCI_SRIOV_ATTRS admin command, a capable device should return the number of free msix vectors +in the global msix pool for its VFs in \field{vfs_free_msix_count} field and also the maximal number of msix vectors that +can be assigned for a single VF in \field{per_vf_max_msix_count} field. In addition, bit 0x0 and bit 0x1 should be set +to indicate on the validity of the other 2 fields in the \field{attrs_mask} field of the result buffer. +See section \ref{sec:Basic Facilities of a Virtio Device / Admin Virtqueues / VIRTIO ADMIN PCI SRIOV ATTRS command} for more +details. + +A PCI PF device may assign default number of MSI-X vectors to the enabled PCI VFs. Also, using VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_SET +it is possible to update the default MSI-X assignment for a specific VF. +In the data of VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_SET admin command, a driver set the virtual function number in +\field{vf_number} and the amount of MSI-X interrupt vectors to configure to the subject virtual function in \field{msix_count}. +In addition, bit 0x0 in the \field{attrs_mask} field should be set. A successful operation guarantees that the requested +amount of MSI-X interrupt vectors was assigned to the subject virtual function. +Also, a successful operation guarantees that the MSI-X capability access by the subject PCI VF defined by the PCI specification must reflect +the new configuration in all relevant fields. For example, by default if the PCI VF has been assigned 4 MSI-X vectors, and VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_SET increases the MSI-X vectors to 8; on this change, reading Table size field of the MSI-X message control +register should reflect a value of 7. +See section \ref{sec:Basic Facilities of a Virtio Device / Admin Virtqueues / VIRTIO ADMIN PCI VF INTERRUPT CONFIG SET command} for more details. + +It is beyond the scope of the virtio specification to define necessary synchronization in system software to ensure that a virtio PCI VF device +interrupt configuration modification is reflected in the PCI device. However, it is expected that any modern system software implementing virtio +drivers and PCI subsystem should ensure that any changes occurring in the VF interrupt configuration is either updated in the PCI VF device or +such configuration fails. + +In the data of VIRTIO_ADMIN_PCI_VF_INTERRUPT_CONFIG_GET admin command, a driver should set the virtual function number in +\field{vf_number}. In addition, bit 0x0 in the \field{attrs_mask} field should be set to indicate requested output fields in +the result from the device. In the result of a successful operation, the amount of MSI-X interrupt vectors that is currently +assigned to the subject virtual function is returned by the device in \field{msix_count} field. In addition, bit 0x0 in the \field{attrs_mask} field should be set by the device to indicate on the validity of \field{msix_count} field. +See section \ref{sec:Basic Facilities of a Virtio Device / Admin Virtqueues / VIRTIO ADMIN PCI VF INTERRUPT CONFIG GET command} for more details. +
I think we should have a guidance on how to provision #msix_vectors step by step. E.g:
1) Do we need to do that before or after the VF provisioning 2) Can the value survive when 0 is wrote to sriov_numvfs etc. Thanks
\section{Virtio Over MMIO}\label{sec:Virtio Transport Options / Virtio Over MMIO}
Virtual environments without PCI support (a common situation in
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