[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] IO-APIC pages being accessed by ACPI methods
>>> On 12.03.13 at 13:51, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote: > On Tue, Mar 12, 2013 at 10:00:08AM +0000, Jan Beulich wrote: >> considering the non-negligible number of systems where firmware >> has ACPI methods that reference IO-APIC pages (causing >> method execution to fail on non-pvops Dom0, and crashing pvops), > > Hmm. I recall only seeing one issue on xen-devel with an IBM box. > Were there more? I recall a couple, but I can't tell whether they weren't all with the same or similar hardware. Some may pre-date your working on Xen though. >> If we do so (and perhaps even independently of this) we probably >> ought to enforce consistent cachability attributes on the secondary >> mappings Dom0 then is able to establish - either by further >> modifying the requested flags, or by outright denying mapping >> requests that aren't specifying UC. While the latter would be my >> preference and would work for the MMCFG case, the ACPI case >> described here wouldn't be covered - Linux'es ACPICA creates >> cachable mappings regardless of whether a SystemMemory is >> RAM or MMIO (thus risking problems even on native). > > Eww. That looks like a bug in the ACPICA? Perhaps my recollection > is incorrect but shouldn't MMIO regions mostly be UC. Only drivers > that know what they are doing (say graphic cards) can choose to > set that to WC? As said - by virtue of the MTRRs being set up right, this works in general. But I do indeed think that this is a latent bug in the ACPICA glue code (the more considering that it's supposed to be arch invariant, yet non-x86 platforms don't necessarily have concepts similar to x86's MTRRs). > Or by cachable mappings you mean WB? Yes, that's the main kind of caching done these days (who cares about WT)? And to avoid misunderstanding - WC to me is not really a cachable memory type, and ACPICA doesn't use it. Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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