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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        LKML <linux-kernel@vger.kernel.org>, X86 Kernel <x86@kernel.org>,
        iommu@lists.linux.dev, Lu Baolu <baolu.lu@linux.intel.com>,
        kvm@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
        Ingo Molnar <mingo@redhat.com>
Cc:     Raj Ashok <ashok.raj@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>, maz@kernel.org,
        peterz@infradead.org, seanjc@google.com,
        Robin Murphy <robin.murphy@arm.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>
Subject: Re: [PATCH RFC 11/13] iommu/vt-d: Add an irq_chip for posted MSIs
In-Reply-To: <20231112041643.2868316-12-jacob.jun.pan@linux.intel.com>
References: <20231112041643.2868316-1-jacob.jun.pan@linux.intel.com>
 <20231112041643.2868316-12-jacob.jun.pan@linux.intel.com>
Date:   Wed, 06 Dec 2023 21:44:02 +0100
Message-ID: <87wmtrt625.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Sat, Nov 11 2023 at 20:16, Jacob Pan wrote:
>  static void fill_msi_msg(struct msi_msg *msg, u32 index, u32 subhandle)
>  {
>  	memset(msg, 0, sizeof(*msg));
> @@ -1361,7 +1397,7 @@ static int intel_irq_remapping_alloc(struct irq_domain *domain,
>  
>  		irq_data->hwirq = (index << 16) + i;
>  		irq_data->chip_data = ird;
> -		irq_data->chip = &intel_ir_chip;
> +		irq_data->chip = posted_msi_supported() ? &intel_ir_chip_post_msi : &intel_ir_chip;

This is just wrong because you change the chip to posted for _ALL_
domains unconditionally.

The only domains which want this chip are the PCI/MSI domains. And those
are distinct from the domains which serve IO/APIC, HPET, no?

So you can set that chip only for PCI/MSI and just let IO/APIC, HPET
domains keep the original chip, which spares any modification of the
IO/APIC domain.