linux-kernel - RE: [PATCH v2 11/13] iommu/vt-d: Make posted MSI an opt-in cmdline option

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Date: Fri, 12 Apr 2024 09:31:32 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>, LKML
	<linux-kernel@...r.kernel.org>, X86 Kernel <x86@...nel.org>, Peter Zijlstra
	<peterz@...radead.org>, "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	Thomas Gleixner <tglx@...utronix.de>, Lu Baolu <baolu.lu@...ux.intel.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Hansen, Dave"
	<dave.hansen@...el.com>, Joerg Roedel <joro@...tes.org>, "H. Peter Anvin"
	<hpa@...or.com>, Borislav Petkov <bp@...en8.de>, Ingo Molnar
	<mingo@...hat.com>
CC: "Luse, Paul E" <paul.e.luse@...el.com>, "Williams, Dan J"
	<dan.j.williams@...el.com>, Jens Axboe <axboe@...nel.dk>, "Raj, Ashok"
	<ashok.raj@...el.com>, "maz@...nel.org" <maz@...nel.org>, "seanjc@...gle.com"
	<seanjc@...gle.com>, Robin Murphy <robin.murphy@....com>,
	"jim.harris@...sung.com" <jim.harris@...sung.com>, "a.manzanares@...sung.com"
	<a.manzanares@...sung.com>, Bjorn Helgaas <helgaas@...nel.org>, "Zeng, Guang"
	<guang.zeng@...el.com>, "robert.hoo.linux@...il.com"
	<robert.hoo.linux@...il.com>
Subject: RE: [PATCH v2 11/13] iommu/vt-d: Make posted MSI an opt-in cmdline
 option

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Saturday, April 6, 2024 6:31 AM
> 
> +#ifdef CONFIG_X86_POSTED_MSI
> +		else if (!strncmp(str, "posted_msi", 10)) {
> +			if (disable_irq_post || disable_irq_remap)
> +				pr_warn("Posted MSI not enabled due to
> conflicting options!");
> +			else
> +				enable_posted_msi = 1;
> +		}
> +#endif

the check of disable_irq_remap is unnecessary. It's unlikely to have
a configuration with disable_irq_post=0 while disable_irq_remap=1
given the latter has bigger scope.

but thinking more do we really need a check here? there is no order
guarantee that "posted_msi" is parsed after the parameters deciding
the value of two disable variables.

it probably makes more sense to just set enable_posted_msi here
and then do all required checks when picking up the irqchip in
intel_irq_remapping_alloc().