[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v3] IOMMU: keep disabled until iommu_setup() is called
>>> On 24.10.12 at 17:49, Jan Beulich wrote: > The iommu is enabled by default when xen is booting and later disabled > in iommu_setup() when no iommu is present. > > But under some circumstances iommu code can be called before > iommu_setup() is processed. If there is no iommu available xen crashes. > > This can happen for example when panic(...) is called as introduced > with the patch "x86-64: detect processors subject to AMD erratum #121 > and refuse to boot" since xen 4.1.3, resulting in > find_iommu_for_device() to be called in the context of > disable_IO_APIC() / __stop_this_cpu(). > > This patch fixes this by keeping the iommu disabled until iommu_setup() > is entered. > > Originally-by: Ronny Hegewald <ronny.hegewald@xxxxxxxxx> > > In order for iommu_enable to be off initially, iommu_supports_eim() > must not depend on it anymore, nor must acpi_parse_dmar(). The former > in turn requires that iommu_intremap gets uncoupled from iommu_enabled > (in particular, failure during IOMMU setup should no longer result in > iommu_intremap getting cleared by generic code; IOMMU specific code > can still do so provided in can live with the consequences). > > This could have the nice side effect of allowing to use "iommu=off" > even when x2APIC was pre-enabled by the BIOS (in which case interrupt > remapping is a requirement, but DMA translation [obviously] isn't), but > that doesn't currently work (and hence x2apic_bsp_setup() forces the > IOMMU on rather than just interrupt remapping). > > For consistency with VT-d, make the AMD IOMMU code also skip all ACPI > table parsing when neither iommu_enable nor iommu_intremap are set. > > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> So after having got acks from both Intel and AMD, I committed this to -unstable, but I'm rather hesitant to backport this onto the 4.x branches (not the least because in the end this is just cosmetic for the problem you reported - the box would not boot in either case, just that with the patch it is more obvious why). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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