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Re: [Xen-devel] [PATCH v2 1/2] AMD/IOMMU: correct handling when XT's prereq features are unavailable

On 28.02.2020 13:41, Roger Pau Monné wrote:
> On Fri, Feb 28, 2020 at 01:10:59PM +0100, Jan Beulich wrote:
>> We should neither cause IOMMU initialization as a whole to fail in this
>> case (we should still be able to bring up the system in non-x2APIC or
>> x2APIC physical mode), nor should the remainder of the function be
>> skipped (as the main part of it won't get entered a 2nd time)
> I'm not sure I see why it won't get entered a second time. AFAICT
> init_done won't be set if amd_iommu_init fails, and hence will be
> called again with xt == false in iov_detect?
>> in such an
>> event. It is merely necessary for the function to indicate to the caller
>> (iov_supports_xt()) that setup failed as far as x2APIC is concerned.
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> LGTM, but it needs to go in with 2/2 AFAICT, or else you would report
> interrupt remapping enabled and x2APIC also enabled but won't handle
> correctly a 32 bit destination field.

Well, this is an improvement on its own imo, even if it doesn't
fully fix everything. The primary point here is to make IOMMU
initialization not fail altogether, when the system could be run
in xAPIC mode.


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