Re: [Xen-devel] [PATCH RFC 5/5] pvh: dom0 boot option to specify iommu rw ranges

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.02.15 at 19:15, <konrad.wilk@xxxxxxxxxx> wrote:
> On Tue, Feb 17, 2015 at 02:14:20PM +0000, Andrew Cooper wrote:
>> On 17/02/15 13:39, Jan Beulich wrote:
>> >>>> On 17.02.15 at 14:32, <andrew.cooper3@xxxxxxxxxx> wrote:
>> >> On 17/02/15 12:36, Jan Beulich wrote:
>> >>>>>> On 14.02.15 at 00:21, <elena.ufimtseva@xxxxxxxxxx> wrote:
>> >>>> On Fri, Feb 13, 2015 at 10:09:39PM +0000, Andrew Cooper wrote:
>> >>>>> If I understand the problem correctly, I believe that the correct
>> >>>>> solution would be to add a dmar_rmrr[ command line parameter along the
>> >>>>> same lines as ivrs_hpet[ and ivrs_ioapic[ which allows the user to
>> >>>>> inject corrections to the ACPI tables via the command line.
>> >>>> Yes, if we agree to classify those magic locations as being not reported
>> >>>> by ACPI machinery.
>> >>> One fundamental problem for someone to use this proposed option
>> >>> in practice is - how does(s)he learn which region(s) to specify?
>> >> Trial and improvement, or find a manual for the affected system.
>> > If such an address range would appear in a manual, it would
>> > almost certainly also appear in the ACPI tables
>> 
>> In an ideal world.
>> 
>> > (unless by manual you mean errata documentation).
>> 
>> Also a valid source of information.
> 
> The way Elena found it is by looking at the EPT violations. Perhaps
> that should be also mentioned in the Documentation for said parameter?

Along with clarifying that this is a rather fragile approach: What if
most of the time you see faults on, say, three (perhaps
consecutive) MFNs and only after many months one on a fourth?
This may be useful for developer purposes, but I very much doubt
this would be of much use for an affected production system.

Jan


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