linux-kernel - Re: [PATCH v3 4/8] x86/psp: Add IRQ support

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Message-ID: <20230328182933.GA1403032@vm02.guest.corp.microsoft.com>
Date:   Tue, 28 Mar 2023 18:29:33 +0000
From:   Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Subject: Re: [PATCH v3 4/8] x86/psp: Add IRQ support

On Wed, Mar 22, 2023 at 11:07:25AM +0100, Thomas Gleixner wrote:
> On Tue, Mar 21 2023 at 20:16, Jeremi Piotrowski wrote:
> > On 21/03/2023 11:31, Thomas Gleixner wrote:
> >  
> >>  1) What's so special about this PSP device that it requires a vector
> >>     directly from the vector domain and evades interrupt remapping?
> >
> > The PSP interrupt configuration requires passing an APIC id and interrupt
> > vector that it will assert. The closest thing I found that provides me with
> > those was the x86_vector_domain. Here's the link to the ACPI interface, the
> > relevant info is on pages 13-15 (it's not very detailed, but that's all I
> > had when implementing this):
> > https://www.amd.com/system/files/TechDocs/58028_1.00-PUB.pdf
> 
> That seriously expects an (extended) APIC-ID so that firmware can fiddle
> with X2APIC ICR directly.
> 
> Why can't firmware people just use something which is properly
> manageable by the OS, e.g. a MSI message or something like the ACPI
> interrupt? Because that would just be too useful and not require
> horrible hacks.
> 
> So my initial suggestion to piggy pack that on device MSI is moot. Let
> me think about it.
> 
> Thanks,
> 
>         tglx
> 
> 

So this is what it looks when done properly with an irq_domain. It definitely
feels less like a hack to me now (thank you): setting affinity works and the
irq is enabled only when requested. The lack of support for interrupt remapping
and the need to configure with APIC-ID/vector comes from the fact that for
firmware designers this PSP operates at the same level as the AMD IOMMU (and
the IOMMU is responsible for interrupt remapping).

Let me know what you think.

Jeremi

View attachment "0001-Drivers-hv-psp-Add-IRQ-support.patch" of type "text/x-diff" (7864 bytes)