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Re: [PATCH] VT-d: Tylersburg errata apply to further steppings

  • To: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 3 Aug 2021 15:06:50 +0200
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Delivery-date: Tue, 03 Aug 2021 13:07:05 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 03.08.2021 15:01, Marek Marczykowski-Górecki wrote:
> On Tue, Aug 03, 2021 at 02:29:01PM +0200, Jan Beulich wrote:
>> On 03.08.2021 14:21, Marek Marczykowski-Górecki wrote:
>>> If we would have an option (in
>>> toolstack, or Xen) to force interrupt remapping, then indeed when it's
>>> broken, PCI passthrough should be refused (or maybe even system should
>>> refuse to boot if we'd have something like iommu=intremap=require). But
>>> none of those actually exists.
>> "iommu=force" actually does prevent boot from completing when
>> interrupt remapping is available, but then gets turned off for
>> some reason. See iommu_setup()'s
>>     bool_t force_intremap = force_iommu && iommu_intremap;
> Ok, then, just setting iommu_intremap=false should do the right thing,

... if "iommu=force" is in use (but not otherwise), ...

> if platform_quirks_init() is called somewhere between the above line,
> and actual enforcement of iommu=force few lines later. I couldn't
> quickly find if that is the case - is it?

-> iommu_hardware_setup()
-> iommu_init_ops->setup() (i.e. vtd_setup())
-> platform_quirks_init()




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