Re: [PATCH v7 7/8] AMD/IOMMU: add "ivmd=" command line option

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 26/08/2021 08:25, Jan Beulich wrote:
> Just like VT-d's "rmrr=" it can be used to cover for firmware omissions.
> Since systems surfacing IVMDs seem to be rare, it is also meant to allow
> testing of the involved code.
>
> Only the IVMD flavors actually understood by the IVMD parsing logic can
> be generated, and for this initial implementation there's also no way to
> control the flags field - unity r/w mappings are assumed.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Reviewed-by: Paul Durrant <paul@xen.org>
> ---
> v5: New.
>
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -836,12 +836,12 @@ Controls for the dom0 IOMMU setup.
>  
>      Typically, some devices in a system use bits of RAM for communication, and
>      these areas should be listed as reserved in the E820 table and identified
> -    via RMRR or IVMD entries in the APCI tables, so Xen can ensure that they
> +    via RMRR or IVMD entries in the ACPI tables, so Xen can ensure that they

Oops.

> @@ -1523,6 +1523,31 @@ _dom0-iommu=map-inclusive_ - using both
>  > `= <integer>`
>  
>  ### irq_vector_map (x86)
> +
> +### ivmd (x86)
> +> `= <start>[-<end>][=<bdf1>[-<bdf1'>][,<bdf2>[-<bdf2'>][,...]]][;<start>...]`
> +
> +Define IVMD-like ranges that are missing from ACPI tables along with the
> +device(s) they belong to, and use them for 1:1 mapping.  End addresses can be
> +omitted when exactly one page is meant.  The ranges are inclusive when start
> +and end are specified.  Note that only PCI segment 0 is supported at this time,
> +but it is fine to specify it explicitly.
> +
> +'start' and 'end' values are page numbers (not full physical addresses),
> +in hexadecimal format (can optionally be preceded by "0x").
> +
> +Omitting the optional (range of) BDF spcifiers signals that the range is to
> +be applied to all devices.
> +
> +Usage example: If device 0:0:1d.0 requires one page (0xd5d45) to be
> +reserved, and devices 0:0:1a.0...0:0:1a.3 collectively require three pages
> +(0xd5d46 thru 0xd5d48) to be reserved, one usage would be:
> +
> +ivmd=d5d45=0:1d.0;0xd5d46-0xd5d48=0:1a.0-0:1a.3
> +
> +Note: grub2 requires to escape or quote special characters, like ';' when
> +multiple ranges are specified - refer to the grub2 documentation.

I'm slightly concerned that we're putting in syntax which the majority
bootloader in use can't handle.

A real IVMD entry in hardware doesn't have the concept of multiple
device ranges, so I think comma ought to be the main list separator, and
I don't think we need ; at all.

~Andrew