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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Feb 19, 2015 at 09:13:52AM +0000, Jan Beulich wrote:
> >>> On 18.02.15 at 19:15, <konrad.wilk@oracle.com> 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@citrix.com> wrote:
> >> >> On 17/02/15 12:36, Jan Beulich wrote:
> >> >>>>>> On 14.02.15 at 00:21, <elena.ufimtseva@oracle.com> 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.

Well, it would help users  - and us providing the arcane incantations
to them - for working around strnage platforms.