RE: [PATCH V5 2/3] HYPERV/IOMMU: Add Hyper-V stub IOMMU driver

[Michael Kelley]

From: Tianyu.Lan@xxxxxxxxxxxxx <Tianyu.Lan@xxxxxxxxxxxxx> Sent: Friday, February 22, 2019 4:12 AM
> 
> On the bare metal, enabling X2APIC mode requires interrupt remapping
> function which helps to deliver irq to cpu with 32-bit APIC ID.
> Hyper-V doesn't provide interrupt remapping function so far and Hyper-V
> MSI protocol already supports to deliver interrupt to the CPU whose
> virtual processor index is more than 255. IO-APIC interrupt still has
> 8-bit APIC ID limitation.
> 
> This patch is to add Hyper-V stub IOMMU driver in order to enable
> X2APIC mode successfully in Hyper-V Linux guest. The driver returns X2APIC
> interrupt remapping capability when X2APIC mode is available. Otherwise,
> it creates a Hyper-V irq domain to limit IO-APIC interrupts' affinity
> and make sure cpus assigned with IO-APIC interrupt have 8-bit APIC ID.
> 
> Define 24 IO-APIC remapping entries because Hyper-V only expose one
> single IO-APIC and one IO-APIC has 24 pins according IO-APIC spec(
> https://pdos.csail.mit.edu/6.828/2016/readings/ia32/ioapic.pdf).
> 
> Signed-off-by: Lan Tianyu <Tianyu.Lan@xxxxxxxxxxxxx>
> ---
> Change since v4:
>        - Fix the loop of scan cpu's APIC id
> 
> Change since v3:
>        - Make Hyper-V IOMMU as Hyper-V default driver
>        - Fix hypervisor_is_type() input parameter
>        - Check possible cpu numbers during scan 0~255 cpu's apic id.
> 
> Change since v2:
>        - Improve comment about why save IO-APIC entry in the irq chip data.
>        - Some code improvement.
>        - Improve statement in the IOMMU Kconfig.
> 
> Change since v1:
>       - Remove unused pr_fmt
>       - Make ioapic_ir_domain as static variable
>       - Remove unused variables cfg and entry in the hyperv_irq_remapping_alloc()
>       - Fix comments

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>