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.\" Copyright (c) 2021 Alexander Motin <mav@FreeBSD.org>
.\" Copyright 2019 Cisco Systems, Inc.
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.Dd October 6, 2022
.Dt VMD 4
.Os
.Sh NAME
.Nm vmd
.Nd Intel Volume Management Device driver
.Sh SYNOPSIS
To compile this driver into the kernel, place the following lines in your
kernel configuration file:
.Bd -ragged -offset -indent
.Cd "device vmd"
.Ed
.Pp
Alternatively, to load the driver as a module at boot time, place the following
line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
vmd_load="YES"
.Ed
.Sh DESCRIPTION
This driver attaches to Intel VMD devices, representing them as PCI-to-PCI
bridges and providing access to children PCI devices via new PCI domains.
Intel VMD is used by Intel's VROC (Virtual RAID on chip) to manage NVMe
drives.
.Sh LOADER TUNABLES
The following tunables are settable via
.Xr loader 8
or
.Xr sysctl 8 :
.Bl -tag -width indent
.It Va hw.vmd.bypass_msi
By default all VMD devices remap children MSI/MSI-X interrupts into their
own. It creates additional isolation, but also complicates things due to
sharing, etc. Fortunately some VMD devices can bypass the remapping.
Defaults to 1.
.It Va hw.vmd.max_msi
Limits number of Message Signaled Interrupt (MSI) vectors allowed to each
child device.
VMD can't distinguish MSI vectors of the same device, so there are no
benefits to have more than one, unless it is required by specific device
driver.
Defaults to 1.
.It Va hw.vmd.max_msix
Limits number of Extended Message Signaled Interrupt (MSI-X) vectors
allowed to each child device.
VMD has limited number of interrupt vectors to map children interrupts into,
so to avoid/reduce sharing children devices/drivers need to be constrained.
Defaults to 3.
.El
.Sh SEE ALSO
.Xr graid 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 13.0 .
