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

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Message-ID: <DM5PR2101MB0918926EDE4D256EC16637A7D77F0@DM5PR2101MB0918.namprd21.prod.outlook.com>
Date:   Fri, 22 Feb 2019 15:58:44 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Tianyu Lan <Tianyu.Lan@...rosoft.com>
CC:     Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "mchehab+samsung@...nel.org" <mchehab+samsung@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "nicolas.ferre@...rochip.com" <nicolas.ferre@...rochip.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        KY Srinivasan <kys@...rosoft.com>,
        vkuznets <vkuznets@...hat.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "sashal@...nel.org" <sashal@...nel.org>,
        "dan.carpenter@...cle.com" <dan.carpenter@...cle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>
Subject: RE: [PATCH V5 2/3] HYPERV/IOMMU: Add Hyper-V stub IOMMU driver

From: Tianyu.Lan@...rosoft.com <Tianyu.Lan@...rosoft.com> 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@...rosoft.com>
> ---
> 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@...rosoft.com>