[virtio-dev] [PATCH v5 0/4] admin: Introduce legacy registers access using AQ

[virtio-dev] [PATCH v5 0/4] admin: Introduce legacy registers access using AQ

[Parav Pandit]

This short series introduces legacy registers access commands for the owner
group member PCI PF to access the legacy registers of the member VFs.

If in future any SIOV devices to support legacy registers, they
can be easily supported using same commands by using the group
member identifiers of the future SIOV devices.

More details as overview, motivation, use case are further described
below.

Patch summary:
--------------
patch-1 split rows of admin opcode tables by a line
patch-2 adds administrative virtuqueue commands
patch-3 adds its conformance section and links

It uses the newly introduced administrative virtqueue facility with 4 new
commands which uses the existing virtio_admin_cmd.

Usecase:
--------
1. A hypervisor/system needs to provide transitional
   virtio devices to the guest VM at scale of thousands,
   typically, one to eight devices per VM.

2. A hypervisor/system needs to provide such devices using a
   vendor agnostic driver in the hypervisor system.

3. A hypervisor system prefers to have single stack regardless of
   virtio device type (net/blk) and be future compatible with a
   single vfio stack using SR-IOV or other scalable device
   virtualization technology to map PCI devices to the guest VM.
   (as transitional or otherwise)

Motivation/Background:
----------------------
The existing virtio transitional PCI device is missing support for
PCI SR-IOV based devices. Currently it does not work beyond
PCI PF, or as software emulated device in reality. Currently it
has below cited system level limitations:

[a] PCIe spec citation:
VFs do not support I/O Space and thus VF BARs shall not indicate I/O Space.

[b] cpu arch citiation:
Intel 64 and IA-32 Architectures Software Developer’s Manual:
The processor’s I/O address space is separate and distinct from
the physical-memory address space. The I/O address space consists
of 64K individually addressable 8-bit I/O ports, numbered 0 through FFFFH.

[c] PCIe spec citation:
If a bridge implements an I/O address range,...I/O address range will be
aligned to a 4 KB boundary.

Overview:
---------
Above usecase requirements is solved by PCI PF group owner accessing
its group member PCI VFs legacy registers using an admin virtqueue of
the group owner PCI PF.

Two new admin virtqueue commands are added which read/write PCI VF
registers.

Software usage example:
-----------------------
One way to use and map to the guest VM is by using vfio driver
framework in Linux kernel.

                +----------------------+
                |pci_dev_id = 0x100X   |
+---------------|pci_rev_id = 0x0      |-----+
|vfio device    |BAR0 = I/O region     |     |
|               |Other attributes      |     |
|               +----------------------+     |
|                                            |
+   +--------------+     +-----------------+ |
|   |I/O BAR to AQ |     | Other vfio      | |
|   |rd/wr mapper  |     | functionalities | |
|   +--------------+     +-----------------+ |
|                                            |
+------+-------------------------+-----------+
       |                         |
       |                    Driver notification
       |                         |
       |                         |
  +----+------------+       +----+------------+
  | +-----+         |       | PCI VF device A |
  | | AQ  |-------------+---->+-------------+ |
  | +-----+         |   |   | | legacy regs | |
  | PCI PF device   |   |   | +-------------+ |
  +-----------------+   |   +-----------------+
                        |
                        |   +----+------------+
                        |   | PCI VF device N |
                        +---->+-------------+ |
                            | | legacy regs | |
                            | +-------------+ |
                            +-----------------+

2. Virtio pci driver to bind to the listed device id and
   use it in the host.

3. Use it in a light weight hypervisor to run bare-metal OS.

Please review.

Alternatives considered:
========================
1. Exposing BAR0 as MMIO BAR that follows legacy registers template
Pros:
a. Kind of works with legacy drivers as some of them have used API
   which is agnostic to MMIO vs IOBAR.
b. Does not require hypervisor intervantion
Cons:
a. Device reset is extremely hard to implement in device at scale as
   driver does not wait for device reset completion
b. Device register width related problems persist that hypervisor if
   wishes, it cannot be fixed.

2. Accessing VF registers by tunneling it through new legacy PCI capability
Pros:
a. Self contained, but cannot work with future PCI SIOV devices
Cons:
a. Equally slow as AQ access
b. Still requires new capability for notification access
c. Requires hardware to build low level registers access which is not worth
   for long term future

3. Accessing VF notification region using new PF BAR
Cons:
a. Requires hardware to build new PCI steering logic per PF to forward
   notification from the PF to VF, requires double the amount of logic
   compared to today
b. Requires very large additional PF BAR whose size must be max_Vfs * BAR size.

4. Trapping CVQ, configuration region, LEGACY_HDR
Cons:
a. This does not fullfil the very basic requirement to not trap the
   1.x objects (configuration registers, vqs)
b. Requires feature negotiations mediation in hypervisor software
c. Requires constant device type specific knowledge in hypervisor driver
   (Does not scale for 30+ device types)

conclusion for picking AQ approach:
==================================
1. Overall AQ based access is simpler to implement with combination of
   best from software and device so that legacy registers do not get baked
   in the device hardware
2. AQ allows hypervisor software to intercept legacy registers and make
   corrections if needed
3. Provides trade-off between performance, device complexity vs spec,
   while still maintaining passthrough mode for the VFs with minimal
   hypervisor intercepts only for legacy registers access
4. AQ mechanism is designed for accessing other member devices registers
   as noted in AQ submission, it utilizes the existing infrastructure over
   other alternatives.
5. Uses existing driver notification region similar to legacy notification
   saves hardware resources

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/167
Signed-off-by: Parav Pandit <parav@nvidia.com>

---
changelog:
v4->v5:
- split pci transport and generic command section to new patch
- removed multiple references to the VF
- written the description of the command as generic with member
  and group device terminology
- reflected many section names to remove VF
- split from pci transport specific patch
- split conformance to transport and generic sections
- written the description of the command as generic with member
  and group device terminology
- reflected many section names to remove VF
- rename fields from register to region
- avoided abbreviation for legacy, device and config
v3->v4:
- moved noted to the conformance section details in next patch
- removed queue notify address query AQ command on Michael's suggestion,
  though it is fine. Instead replaced with extending virtio_pci_notify_cap
  to indicate that legacy queue notifications can be done on the
  notification location
- fixed spelling errors
- replaced administrative virtqueue to administration virtqueue
- moved legacy interface normative references to legacy conformance
  section
v2->v3:
- added new patch to split raws of admin vq opcode table
- adddressed Jason and Michael's comment to split single register
  access command to common config and device specific commands.
- dropped the suggetion to introduce enable/disable command as
  admin command cap bit already covers it.
- added other alternative design considered and discussed in detail in v0, v1 and v2
v1->v2:
- addressed comments from Michael
- added theory of operation
- grammar corrections
- removed group fields description from individual commands as
  it is already present in generic section
- added endianness normative for legacy device registers region
- renamed the file to drop vf and add legacy prefix
- added overview in commit log
- renamed subsection to reflect command
v0->v1:
- addressed comments, suggesetions and ideas from Michael Tsirkin and Jason Wang
- far more simpler design than MMR access
- removed complexities of MMR device ids
- removed complexities of MMR registers and extended capabilities
- dropped adding new extended capabilities because if if they are
  added, a pci device still needs to have existing capabilities
  in the legacy configuration space and hypervisor driver do not
  need to access them


Parav Pandit (4):
  admin: Split opcode table rows with a line
  admin: Fix section numbering
  admin: Add group member legacy register access commands
  transport-pci: Introduce group legacy group member config region
    access

 admin-cmds-legacy-access.tex  | 136 ++++++++++++++++++++++++++++++++++
 admin.tex                     |  18 ++++-
 conformance.tex               |   5 ++
 transport-pci-legacy-regs.tex |  46 ++++++++++++
 transport-pci.tex             |  19 +++++
 5 files changed, 221 insertions(+), 3 deletions(-)
 create mode 100644 admin-cmds-legacy-access.tex
 create mode 100644 transport-pci-legacy-regs.tex

-- 
2.26.2


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[virtio-dev] [PATCH v5 1/4] admin: Split opcode table rows with a line

[Parav Pandit]

Currently all opcode appears to be in a single row.
Separate them with a line similar to other tables.

Signed-off-by: Parav Pandit <parav@nvidia.com>
---
changelog:
v2->v3:
- new patch
---
 admin.tex | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/admin.tex b/admin.tex
index 2efd4d7..e51f9e6 100644
--- a/admin.tex
+++ b/admin.tex
@@ -114,7 +114,9 @@ \subsection{Group administration commands}\label{sec:Basic Facilities of a Virti
 opcode & Name & Command Description \\
 \hline \hline
 0x0000 & VIRTIO_ADMIN_CMD_LIST_QUERY & Provides to driver list of commands supported for this group type    \\
+\hline
 0x0001 & VIRTIO_ADMIN_CMD_LIST_USE & Provides to device list of commands used for this group type \\
+\hline
 0x0002 - 0x7FFF & - & Commands using \field{struct virtio_admin_cmd}    \\
 \hline
 0x8000 - 0xFFFF & - & Reserved for future commands (possibly using a different structure)    \\
-- 
2.26.2


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[virtio-dev] [PATCH v5 2/4] admin: Fix section numbering

[Parav Pandit]

Requirements are put one additional level down. Fix it.

Signed-off-by: Parav Pandit <parav@nvidia.com>
---
changelog:
v4->v5:
- new patch
---
 admin.tex | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/admin.tex b/admin.tex
index e51f9e6..fd3b97d 100644
--- a/admin.tex
+++ b/admin.tex
@@ -286,7 +286,7 @@ \subsection{Group administration commands}\label{sec:Basic Facilities of a Virti
 supporting multiple group types, the list of supported commands
 might differ between different group types.
 
-\devicenormative{\paragraph}{Group administration commands}{Basic Facilities of a Virtio Device / Device groups / Group administration commands}
+\devicenormative{\subsubsection}{Group administration commands}{Basic Facilities of a Virtio Device / Device groups / Group administration commands}
 
 The device MUST validate \field{opcode}, \field{group_type} and
 \field{group_member_id}, and if any of these has an invalid or
@@ -378,7 +378,7 @@ \subsection{Group administration commands}\label{sec:Basic Facilities of a Virti
 \field{VF Enable} refer to registers within the SR-IOV Extended
 Capability as specified by \hyperref[intro:PCIe]{[PCIe]}.
 
-\drivernormative{\paragraph}{Group administration commands}{Basic Facilities of a Virtio Device / Device groups / Group administration commands}
+\drivernormative{\subsubsection}{Group administration commands}{Basic Facilities of a Virtio Device / Device groups / Group administration commands}
 
 The driver MAY discover whether device supports a specific group type
 by issuing VIRTIO_ADMIN_CMD_LIST_QUERY with the matching
-- 
2.26.2


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[virtio-dev] [PATCH v5 3/4] admin: Add group member legacy register access commands

[Parav Pandit]

Introduce group member legacy common configuration and legacy device
configuration access read/write commands.

Group member legacy registers access commands enable group owner driver
software to access legacy registers on behalf of the guest virtual
machine.

Usecase:
========
1. A hypervisor/system needs to provide transitional
   virtio devices to the guest VM at scale of thousands,
   typically, one to eight devices per VM.

2. A hypervisor/system needs to provide such devices using a
   vendor agnostic driver in the hypervisor system.

3. A hypervisor system prefers to have single stack regardless of
   virtio device type (net/blk) and be future compatible with a
   single vfio stack using SR-IOV or other scalable device
   virtualization technology to map PCI devices to the guest VM.
   (as transitional or otherwise)

Motivation/Background:
=====================
The existing virtio transitional PCI device is missing support for
PCI SR-IOV based devices. Currently it does not work beyond
PCI PF, or as software emulated device in reality. Currently it
has below cited system level limitations:

[a] PCIe spec citation:
VFs do not support I/O Space and thus VF BARs shall not indicate I/O Space.

[b] cpu arch citiation:
Intel 64 and IA-32 Architectures Software Developer’s Manual:
The processor’s I/O address space is separate and distinct from
the physical-memory address space. The I/O address space consists
of 64K individually addressable 8-bit I/O ports, numbered 0 through FFFFH.

[c] PCIe spec citation:
If a bridge implements an I/O address range,...I/O address range will be
aligned to a 4 KB boundary.

Overview:
=========
Above usecase requirements is solved by PCI PF group owner accessing
its group member PCI VFs legacy registers using an admin virtqueue of
the group owner PCI PF.

Two types of administration commands are added which read/write PCI VF
registers.

Software usage example:
=======================

1. One way to use and map to the guest VM is by using vfio driver
framework in Linux kernel.

                +----------------------+
                |pci_dev_id = 0x100X   |
+---------------|pci_rev_id = 0x0      |-----+
|vfio device    |BAR0 = I/O region     |     |
|               |Other attributes      |     |
|               +----------------------+     |
|                                            |
+   +--------------+     +-----------------+ |
|   |I/O BAR to AQ |     | Other vfio      | |
|   |rd/wr mapper  |     | functionalities | |
|   +--------------+     +-----------------+ |
|                                            |
+------+-------------------------+-----------+
       |                         |
       |                         |
       |                  Driver notifications
       |                         |
  +----+------------+       +----+------------+
  | +-----+         |       | PCI VF device A |
  | | AQ  |-------------+---->+-------------+ |
  | +-----+         |   |   | | legacy regs | |
  | PCI PF device   |   |   | +-------------+ |
  +-----------------+   |   +-----------------+
                        |
                        |   +----+------------+
                        |   | PCI VF device N |
                        +---->+-------------+ |
                            | | legacy regs | |
                            | +-------------+ |
                            +-----------------+

2. Continue to use the virtio pci driver to bind to the
   listed device id and use it as in the host.

3. Use it in a light weight hypervisor to run bare-metal OS.

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/167
Signed-off-by: Parav Pandit <parav@nvidia.com>
---
changelog:
v4->v5:
- split from pci transport specific patch
- split conformance to transport and generic sections
- written the description of the command as generic with member
  and group device terminology
- reflected many section names to remove VF
- rename fields from register to region
- avoided abbreviation for legacy, device and config
---
 admin-cmds-legacy-access.tex | 136 +++++++++++++++++++++++++++++++++++
 admin.tex                    |  12 +++-
 conformance.tex              |   2 +
 3 files changed, 149 insertions(+), 1 deletion(-)
 create mode 100644 admin-cmds-legacy-access.tex

diff --git a/admin-cmds-legacy-access.tex b/admin-cmds-legacy-access.tex
new file mode 100644
index 0000000..bcb6d9e
--- /dev/null
+++ b/admin-cmds-legacy-access.tex
@@ -0,0 +1,136 @@
+\subsubsection{Legacy Interfaces: legacy configuration access commands}\label{sec:Basic Facilities of a Virtio Device / Device groups / Group
+administration commands / Legacy Interfaces: legacy configuration access commands}
+
+The group owner device can optionally enable the driver to access its member devices legacy common
+configuration and device configuration region using following listed
+administrative commands:
+
+\begin{enumerate}
+\item Legacy Common Configuration Region Write Command
+\item Legacy common Configuration Region Read Command
+\item Legacy Device Configuration Region Write Command
+\item Legacy Device Configuration Region Read Command
+\end{enumerate}
+
+\paragraph{Legacy Common Configuration Region Write Command}\label{par:Basic Facilities of a Virtio Device / Device groups / Group
+administration commands / Legacy Interfaces: legacy configuration access commands / Legacy Common Configuration Region Write Command}
+
+This command writes in a legacy common configuration region of a group member device.
+This command follows \field{struct virtio_admin_cmd}.
+This command uses following structure for \field{command_specific_data}:
+
+\begin{lstlisting}
+struct virtio_admin_cmd_legacy_common_cfg_wr_data {
+	u8 offset; /* Starting byte offset of the common configuration region to write */
+	u8 region_data[];
+};
+\end{lstlisting}
+
+The driver sets command \field{opcode} to VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_WRITE.
+The driver sets valid \field{offset} and associated \field{region_data} bytes to
+write to the common configuration region.
+
+This command does not have any command specific result.
+
+\paragraph{Legacy Common Configuration Region Read Command}\label{par:Basic Facilities of a Virtio Device / Device groups / Group administration commands / Legacy Interfaces: legacy configuration access commands / Legacy Common Configuration Region Read Command}
+
+This command reads from a legacy common configuration region of a group member device.
+This command follows \field{struct virtio_admin_cmd}.
+This command uses following listed structure for \field{command_specific_data}:
+
+\begin{lstlisting}
+struct virtio_admin_cmd_legacy_common_cfg_rd_data {
+	u8 offset; /* Starting byte offset of the common configuration region to read */
+};
+\end{lstlisting}
+
+The driver sets command \field{opcode} to VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_READ.
+
+The driver sets valid \field{offset} of the region from where to read
+\field{region_data}.
+
+When command completes successfully, \field{command_specific_result}
+uses following listed structure:
+
+\begin{lstlisting}
+struct virtio_admin_cmd_legacy_common_cfg_rd_result {
+	u8 region_data[];
+};
+\end{lstlisting}
+
+\paragraph{Legacy Device Configuration Region Write Command}\label{par:Basic Facilities of a Virtio Device / Device groups / Group administration commands / Legacy Interfaces: legacy configuration access commands / Legacy Device Configuration Region Write Command}
+
+This command writes in a legacy device configuration registers of a group member device.
+This command follows \field{struct virtio_admin_cmd}.
+This command uses following structure for \field{command_specific_data}:
+
+\begin{lstlisting}
+struct virtio_admin_cmd_ld_reg_wr_data {
+	u8 offset; /* Starting byte offset of the device configuration region to write */
+	u8 region_data[];
+};
+\end{lstlisting}
+
+The driver sets command \field{opcode} to VIRTIO_ADMIN_CMD_LEGACY_DEV_REG_WRITE.
+The driver sets valid \field{offset} and associated \field{region_data} bytes to
+the device configuration region.
+
+This command does not have any command specific result.
+
+\paragraph{Legacy Device Registers Read Command}\label{par:Basic Facilities of a Virtio Device / Device groups / Group administration commands / Legacy Interfaces: legacy configuration access commands / Legacy Device Configuration Region Read Command}
+
+This command reads from a legacy device configuration region of a group member device.
+This command follows \field{struct virtio_admin_cmd}.
+
+This command uses following listed structure for \field{command_specific_data}:
+
+\begin{lstlisting}
+struct virtio_admin_cmd_legacy_dev_cfg_rd_data {
+	u8 offset; /* Starting byte offset of the device configuration region to read */
+};
+\end{lstlisting}
+
+The driver sets command \field{opcode} to VIRTIO_ADMIN_CMD_LD_REG_READ.
+The driver sets valid \field{offset} of the device configurationi region from
+where to read \field{region_data}.
+
+When command completes successfully, \field{command_specific_result}
+uses following listed structure:
+
+\begin{lstlisting}
+struct virtio_admin_cmd_ld_reg_rd_result {
+	u8 region_data[];
+};
+\end{lstlisting}
+
+\devicenormative{\paragraph}{Legacy Interfaces: legacy configuration access commands}{Basic Facilities of a Virtio Device / Device groups / Group administration commands / Legacy Interfaces: legacy configuration access commands}
+
+If the group owner device supports legacy registers access for its group members,
+the device MUST set all corresponding bits for commands VIRTIO_ADMIN_CMD_LCC_REG_WRITE,
+VIRTIO_ADMIN_CMD_LCC_REG_READ, VIRTIO_ADMIN_CMD_LD_REG_WRITE,
+VIRTIO_ADMIN_CMD_LD_REG_READ in the command result of
+VIRTIO_ADMIN_CMD_LIST_QUERY in \field{device_admin_cmd_opcodes}.
+
+The device MUST encode and decode legacy device specific registers using
+little-endian format.
+
+The device MUST fail VIRTIO_ADMIN_CMD_LCC_REG_WRITE, VIRTIO_ADMIN_CMD_LCC_REG_READ
+commands for the invalid offset which is outside the legacy common configuration
+register's address range.
+
+The device MUST fail VIRTIO_ADMIN_CMD_LD_REG_WRITE, VIRTIO_ADMIN_CMD_LD_REG_READ
+commands for the invalid offset which is outside the legacy device specific
+register's address range.
+
+\drivernormative{\paragraph}{Legacy Interfaces: legacy configuration access commands}{Basic Facilities of a Virtio Device / Device groups / Group administration commands / Legacy Interfaces: legacy configuration access commands}
+
+The driver MUST encode and decode legacy device specific registers using
+little-endian format.
+
+The driver SHOULD send VIRTIO_ADMIN_CMD_LCC_REG_WRITE and
+VIRTIO_ADMIN_CMD_LCC_REG_READ commands with a valid offset which is in the
+legacy common configuration region address range.
+
+The driver SHOULD send commands VIRTIO_ADMIN_CMD_LD_REG_WRITE and
+VIRTIO_ADMIN_CMD_LD_REG_READ with a valid offset which is in the legacy
+device specific configuration region address range.
diff --git a/admin.tex b/admin.tex
index fd3b97d..49a0b6f 100644
--- a/admin.tex
+++ b/admin.tex
@@ -117,7 +117,15 @@ \subsection{Group administration commands}\label{sec:Basic Facilities of a Virti
 \hline
 0x0001 & VIRTIO_ADMIN_CMD_LIST_USE & Provides to device list of commands used for this group type \\
 \hline
-0x0002 - 0x7FFF & - & Commands using \field{struct virtio_admin_cmd}    \\
+0x0002 & VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_WRITE & Write legacy common configuration region of a member device \\
+\hline
+0x0003 & VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_READ & Read legacy common configuration region of a member device \\
+\hline
+0x0004 & VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_WRITE & Write legacy device configuration region of a member device \\
+\hline
+0x0005 & VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_READ & Read legacy device configuration region of a member device \\
+\hline
+0x0006 - 0x7FFF & - & Commands using \field{struct virtio_admin_cmd}    \\
 \hline
 0x8000 - 0xFFFF & - & Reserved for future commands (possibly using a different structure)    \\
 \hline
@@ -286,6 +294,8 @@ \subsection{Group administration commands}\label{sec:Basic Facilities of a Virti
 supporting multiple group types, the list of supported commands
 might differ between different group types.
 
+\input{admin-cmds-legacy-access.tex}
+
 \devicenormative{\subsubsection}{Group administration commands}{Basic Facilities of a Virtio Device / Device groups / Group administration commands}
 
 The device MUST validate \field{opcode}, \field{group_type} and
diff --git a/conformance.tex b/conformance.tex
index 01ccd69..6bac4b0 100644
--- a/conformance.tex
+++ b/conformance.tex
@@ -260,6 +260,8 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \item Section \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Legacy Interfaces: A Note on Virtqueue Layout}
 \item Section \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Legacy Interfaces: A Note on Virtqueue Endianness}
 \item Section \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Message Framing / Legacy Interface: Message Framing}
+\item Section \ref{devicenormative:Basic Facilities of a Virtio Device / Device groups / Group administration commands / Legacy Interfaces: legacy configuration access commands}
+\item Section \ref{drivernormative:Basic Facilities of a Virtio Device / Device groups / Group administration commands / Legacy Interfaces: legacy configuration access commands}
 \item Section \ref{sec:General Initialization And Device Operation / Device Initialization / Legacy Interface: Device Initialization}
 \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Discovery / Legacy Interfaces: A Note on PCI Device Discovery}
 \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Legacy Interfaces: A Note on PCI Device Layout}
-- 
2.26.2


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[virtio-dev] [PATCH v5 4/4] transport-pci: Introduce group legacy group member config region access

[Parav Pandit]

This patch links how in a PCI transport a group owner can access group
member (PCI VFs) legacy registers using a legacy registers access
commands using administration virtqueue infrastructure.

Additionally it extend the PCI notification capability through which a
PCI VF device indicates to the driver which PCI BAR region to be used
for driver notifications.

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/167
Signed-off-by: Parav Pandit <parav@nvidia.com>
---
changelog:
v4->v5:
- split pci transport and generic command section to new patch
- removed multiple references to the VF
- written the description of the command as generic with member
  and group device terminology
- reflected many section names to remove VF
v3->v4:
- moved noted to the conformance section details in next patch
- removed queue notify address query AQ command on Michael's suggestion,
  though it is fine. Instead replaced with extending virtio_pci_notify_cap
  to indicate that legacy queue notifications can be done on the
  notification location.
- fixed spelling errors.
- replaced administrative virtqueue to administration virtqueue
- added queue notification capability register to indicate legacy q
  notification supported
v2->v3:
- adddressed Jason and Michael's comment to split single register
  access command to common config and device specific commands.
- dropped the suggetion to introduce enable/disable command as
  admin command cap bit already covers it.
v1->v2:
- addressed comments from Michael
- added theory of operation
- grammar corrections
- removed group fields description from individual commands as
  it is already present in generic section
- added endianness normative for legacy device registers region
- renamed the file to drop vf and add legacy prefix

- added overview in commit log
- renamed subsection to reflect command
---
 conformance.tex               |  3 +++
 transport-pci-legacy-regs.tex | 46 +++++++++++++++++++++++++++++++++++
 transport-pci.tex             | 19 +++++++++++++++
 3 files changed, 68 insertions(+)
 create mode 100644 transport-pci-legacy-regs.tex

diff --git a/conformance.tex b/conformance.tex
index 6bac4b0..93f409c 100644
--- a/conformance.tex
+++ b/conformance.tex
@@ -267,6 +267,9 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets}
 \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Legacy Interfaces: A Note on PCI Device Layout}
 \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Virtio Device Configuration Layout Detection / Legacy Interface: A Note on Device Layout Detection}
 \item Section \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Device Initialization / Virtqueue Configuration / Legacy Interface: A Note on Virtqueue Configuration}
+\item Section \ref{devicenormative:Virtio Transport Options / Virtio Over PCI Bus / Legacy Interfaces Requirements: Group Member Device Legacy Configuration Access}
+\item Section \ref{drivernormative:Virtio Transport Options / Virtio Over PCI Bus / Legacy Interfaces Requirements: Group Member Device Legacy Configuration Access}
+\item Section \ref{par:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Legacy Interfaces: Notification capability}
 \item Section \ref{sec:Virtio Transport Options / Virtio Over MMIO / Legacy interface}
 \item Section \ref{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Setting the Virtio Revision / Legacy Interfaces: A Note on Setting the Virtio Revision}
 \item Section \ref{sec:Virtio Transport Options / Virtio over channel I/O / Device Initialization / Configuring a Virtqueue / Legacy Interface: A Note on Configuring a Virtqueue}
diff --git a/transport-pci-legacy-regs.tex b/transport-pci-legacy-regs.tex
new file mode 100644
index 0000000..a25b586
--- /dev/null
+++ b/transport-pci-legacy-regs.tex
@@ -0,0 +1,46 @@
+\subsection{Legacy Interfaces: Group member device Configuration Region Access}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / Legacy Interfaces: Group Member Device Configuration Region Access}
+
+As described in PCIe base specification \hyperref[intro:PCIe]{[PCIe]} PCI VFs
+do not support the I/O space BAR. Due to this limitation, a PCI VF hardware
+device that supports legacy interfaces cannot be attached as passthrough
+device to the guest virtual machine.
+
+To have a transitional or legacy virtio device in the guest virtual machine,
+a PCI PF device as a group owner may support accessing its group member
+device's legacy configuration region using the group administration commands
+listed at \ref{sec:Basic Facilities of a Virtio Device / Device groups / Group
+administration commands / Legacy Interfaces: legacy configuration access commands}.
+These legacy configuration access commands are transported via the
+administration virtqueue. This mechanism enables minimal involvement of the
+hypervisor software only for the purpose of the legacy configuration region access.
+
+When a guest virtual machine requests legacy configuration and device
+specific regions of group member device, a hypervisor software accesses
+it using an administration virtqueue on behalf of the guest virtual machine.
+
+Even though virtqueue driver notifications can be communicated through
+administration virtqueue, if the group member device support such
+notifications using a memory-mapped operation, such driver notifications
+are sent using a group member device defined notification region.
+
+The group owner device should not expose PCI BAR0 for the group member
+devices when it prefers to support legacy interface for legacy configuration
+access using its group owner.
+This facilitates hypervisor software to operate with least amount of
+complexities to emulate the legacy interface I/O space BAR and passthrough
+other PCI BARs and PCI device capabilities to the guest virtual machine
+without any translation.
+
+\devicenormative{\subsubsection}{Legacy Interfaces Requirements: Group Member Device Legacy Configuration Access}{Virtio Transport Options / Virtio Over PCI Bus / Legacy Interfaces Requirements: Group Member Device Legacy Configuration Access}
+
+When a PCI SR-IOV group owner device supports
+VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_READ,
+VIRTIO_ADMIN_CMD_LEGACY_COMMON_CFG_WRITE, VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_READ,
+VIRTIO_ADMIN_CMD_LEGACY_DEV_CFG_WRITE commands, the group owner device SHOULD
+NOT expose PCI BAR0 in the SR-IOV Extended capability. This is to facilitate the
+software to emulate I/O region BAR0 for supporting the legacy interface.
+
+\drivernormative{\subsubsection}{Legacy Interfaces Requirements: Group Member Device Legacy Configuration Access}{Virtio Transport Options / Virtio Over PCI Bus / Legacy Interfaces Requirements: Group Member Device Legacy Configuration Access}
+
+The driver SHOULD NOT emulate I/O region BAR0 if a device group member exposes
+a PCI BAR0.
diff --git a/transport-pci.tex b/transport-pci.tex
index a5c6719..42bc104 100644
--- a/transport-pci.tex
+++ b/transport-pci.tex
@@ -541,6 +541,7 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 struct virtio_pci_notify_cap {
         struct virtio_pci_cap cap;
         le32 notify_off_multiplier; /* Multiplier for queue_notify_off. */
+        u8 legacy_q_notify_supported;
 };
 \end{lstlisting}
 
@@ -560,6 +561,14 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 the same Queue Notify address for all queues.
 \end{note}
 
+\field{legacy_q_notify_supported} when set to 1, indicates that the device
+supports legacy queue notifications at this notification location. Legacy Queue
+Notification address is derived within a BAR for a virtqueue:
+
+\begin{lstlisting}
+        cap.offset
+\end{lstlisting}
+
 \devicenormative{\paragraph}{Notification capability}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
 The device MUST present at least one notification capability.
 
@@ -596,6 +605,14 @@ \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options
 cap.length >= queue_notify_off * notify_off_multiplier + 4
 \end{lstlisting}
 
+\paragraph{Legacy Interfaces: Notification capability}\label{par:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Legacy Interfaces: Notification capability}
+
+The device SHOULD set \field{legacy_q_notify_supported} when the device
+notification location supports legacy driver notifications.
+
+The driver in the hypervisor MAY use notification location for accessing
+legacy queue notify address when the device supports it.
+
 \subsubsection{ISR status capability}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / ISR status capability}
 
 The VIRTIO_PCI_CAP_ISR_CFG capability
@@ -1212,3 +1229,5 @@ \subsubsection{Driver Handling Interrupts}\label{sec:Virtio Transport Options /
         re-examine the configuration space to see what changed.
     \end{itemize}
 \end{itemize}
+
+\input{transport-pci-legacy-regs.tex}
-- 
2.26.2


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