linux-kernel - [PATCH 12/15] iommu/vt-d: Make posted MSI an opt-in cmdline option

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Date: Fri, 26 Jan 2024 15:42:34 -0800
From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
To: LKML <linux-kernel@...r.kernel.org>,
	X86 Kernel <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	iommu@...ts.linux.dev,
	Thomas Gleixner <tglx@...utronix.de>,
	"Lu Baolu" <baolu.lu@...ux.intel.com>,
	kvm@...r.kernel.org,
	Dave Hansen <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: Paul Luse <paul.e.luse@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Jens Axboe <axboe@...nel.dk>,
	Raj Ashok <ashok.raj@...el.com>,
	"Tian, Kevin" <kevin.tian@...el.com>,
	maz@...nel.org,
	seanjc@...gle.com,
	"Robin Murphy" <robin.murphy@....com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: [PATCH 12/15] iommu/vt-d: Make posted MSI an opt-in cmdline option

Add a command line opt-in option for posted MSI if CONFIG_X86_POSTED_MSI=y.

Also introduce a helper function for testing if posted MSI is supported on
the platform.

Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  1 +
 arch/x86/include/asm/irq_remapping.h            | 11 +++++++++++
 drivers/iommu/irq_remapping.c                   | 13 ++++++++++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 31b3a25680d0..35feefc0bdb0 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2212,6 +2212,7 @@
 			no_x2apic_optout
 				BIOS x2APIC opt-out request will be ignored
 			nopost	disable Interrupt Posting
+			posted_msi enable MSIs delivered as posted interrupts
 
 	iomem=		Disable strict checking of access to MMIO memory
 		strict	regions from userspace.
diff --git a/arch/x86/include/asm/irq_remapping.h b/arch/x86/include/asm/irq_remapping.h
index 7a2ed154a5e1..e46bde61029b 100644
--- a/arch/x86/include/asm/irq_remapping.h
+++ b/arch/x86/include/asm/irq_remapping.h
@@ -50,6 +50,17 @@ static inline struct irq_domain *arch_get_ir_parent_domain(void)
 	return x86_vector_domain;
 }
 
+#ifdef CONFIG_X86_POSTED_MSI
+extern int enable_posted_msi;
+
+static inline bool posted_msi_supported(void)
+{
+	return enable_posted_msi && irq_remapping_cap(IRQ_POSTING_CAP);
+}
+#else
+static inline bool posted_msi_supported(void) { return false; };
+#endif
+
 #else  /* CONFIG_IRQ_REMAP */
 
 static inline bool irq_remapping_cap(enum irq_remap_cap cap) { return 0; }
diff --git a/drivers/iommu/irq_remapping.c b/drivers/iommu/irq_remapping.c
index 83314b9d8f38..4047ac396728 100644
--- a/drivers/iommu/irq_remapping.c
+++ b/drivers/iommu/irq_remapping.c
@@ -24,6 +24,10 @@ int no_x2apic_optout;
 
 int disable_irq_post = 0;
 
+#ifdef CONFIG_X86_POSTED_MSI
+int enable_posted_msi;
+#endif
+
 static int disable_irq_remap;
 static struct irq_remap_ops *remap_ops;
 
@@ -70,7 +74,14 @@ static __init int setup_irqremap(char *str)
 			no_x2apic_optout = 1;
 		else if (!strncmp(str, "nopost", 6))
 			disable_irq_post = 1;
-
+#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
 		str += strcspn(str, ",");
 		while (*str == ',')
 			str++;
-- 
2.25.1