linux-kernel - Re: [RFC PATCH 5/5] xen/privcmd: add IOCTL_PRIVCMD_GSI_FROM

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Date:   Wed, 15 Mar 2023 15:26:17 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Huang Rui <ray.huang@....com>
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        Stewart Hildebrand <Stewart.Hildebrand@....com>,
        Xenia Ragiadakou <burzalodowa@...il.com>,
        Honglei Huang <honglei1.huang@....com>,
        Julia Zhang <julia.zhang@....com>,
        Chen Jiqian <Jiqian.Chen@....com>
Subject: Re: [RFC PATCH 5/5] xen/privcmd: add IOCTL_PRIVCMD_GSI_FROM_IRQ

On Sun, Mar 12, 2023 at 08:01:57PM +0800, Huang Rui wrote:
> From: Chen Jiqian <Jiqian.Chen@....com>
> 
> When hypervisor get an interrupt, it needs interrupt's
> gsi number instead of irq number. Gsi number is unique
> in xen, but irq number is only unique in one domain.
> So, we need to record the relationship between irq and
> gsi when dom0 initialized pci devices, and provide syscall
> IOCTL_PRIVCMD_GSI_FROM_IRQ to translate irq to gsi. So
> that, we can map pirq successfully in hypervisor side.

GSI is not only unique in Xen, it's an ACPI provided value that's
unique in the platform.  The text above make it look like GSI is some
kind of internal Xen reference to an interrupt, but it's not.

How does a PV domain deal with this? I would assume there Linux will
also end up with IRQ != GSI, and hence will need some kind of
translation?

Thanks, Roger.