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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>,
        linux-kernel@vger.kernel.org
Cc:     Brijesh Singh <brijesh.singh@amd.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        "Kalra, Ashish" <ashish.kalra@amd.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org
Subject: Re: [PATCH v3 4/8] x86/psp: Add IRQ support
In-Reply-To: <89c227a5-0db6-7cbe-6beb-4035f58f036b@linux.microsoft.com>
References: <20230320191956.1354602-1-jpiotrowski@linux.microsoft.com>
 <20230320191956.1354602-5-jpiotrowski@linux.microsoft.com>
 <87h6ue9z0p.ffs@tglx>
 <89c227a5-0db6-7cbe-6beb-4035f58f036b@linux.microsoft.com>
Date:   Wed, 22 Mar 2023 11:07:25 +0100
Message-ID: <877cv99k0y.ffs@tglx>
MIME-Version: 1.0
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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