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

[Jan Beulich <jbeulich@suse.com>]

On 26.08.2021 16:08, Andrew Cooper wrote:
> On 26/08/2021 08:25, Jan Beulich wrote:
>> @@ -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.

This matches RMRR handling, and I'd really like to keep the two as
similar as possible. Plus you can avoid the use of ; also by having
more than one "ivmd=" on the command line.

> 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.

Firmware would need to present two IVMD entries in such a case. On
the command line I think we should allow more compact representation.
Plus again - this is similar to "rmrr=".

Jan