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From:   Dexuan Cui <decui@microsoft.com>
To:     "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "x86@kernel.org" <x86@kernel.org>
CC:     "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
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        Josh Poulson <jopoulso@microsoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>
Subject: [PATCH] x86/hyperv: suppress "PCI: Fatal: No config space access
 function found"
Thread-Topic: [PATCH] x86/hyperv: suppress "PCI: Fatal: No config space access
 function found"
Thread-Index: AdRPnqLjk5RKpcSXRi2tGnIAPJn6lQ==
Date:   Tue, 18 Sep 2018 22:29:50 +0000
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A Generatin-2 Linux VM on Hyper-V doesn't have the legacy PCI bus, and
users always see the scary warning, which is actually harmless. The patch
is made to suppress the warning.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
---
 arch/x86/hyperv/hv_init.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 20c876c..7abb09e 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -17,6 +17,7 @@
  *
  */
=20
+#include <linux/efi.h>
 #include <linux/types.h>
 #include <asm/apic.h>
 #include <asm/desc.h>
@@ -253,6 +254,22 @@ static int hv_cpu_die(unsigned int cpu)
 	return 0;
 }
=20
+static int __init hv_pci_init(void)
+{
+	int gen2vm =3D efi_enabled(EFI_BOOT);
+
+	/*
+	 * For Generation-2 VM, we exit from pci_arch_init() by returning 0.
+	 * The purpose is to suppress the harmless warning:
+	 * "PCI: Fatal: No config space access function found"
+	 */
+	if (gen2vm)
+		return 0;
+
+	/* For Generation-1 VM, we'll proceed in pci_arch_init().  */
+	return 1;
+}
+
 /*
  * This function is to be invoked early in the boot sequence after the
  * hypervisor has been detected.
@@ -329,6 +346,8 @@ void __init hyperv_init(void)
=20
 	hv_apic_init();
=20
+	x86_init.pci.arch_init =3D hv_pci_init;
+
 	/*
 	 * Register Hyper-V specific clocksource.
 	 */
--=20
2.7.4