linux-kernel - [RFC 17/18] pci: Don't clear bus master is persistence enabled

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Message-ID: <20240205120203.60312-18-jgowans@amazon.com>
Date: Mon, 5 Feb 2024 12:02:02 +0000
From: James Gowans <jgowans@...zon.com>
To: <linux-kernel@...r.kernel.org>
CC: Eric Biederman <ebiederm@...ssion.com>, <kexec@...ts.infradead.org>,
	"Joerg Roedel" <joro@...tes.org>, Will Deacon <will@...nel.org>,
	<iommu@...ts.linux.dev>, Alexander Viro <viro@...iv.linux.org.uk>, "Christian
 Brauner" <brauner@...nel.org>, <linux-fsdevel@...r.kernel.org>, Paolo Bonzini
	<pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>,
	<kvm@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>,
	<linux-mm@...ck.org>, Alexander Graf <graf@...zon.com>, David Woodhouse
	<dwmw@...zon.co.uk>, "Jan H . Schoenherr" <jschoenh@...zon.de>, Usama Arif
	<usama.arif@...edance.com>, Anthony Yznaga <anthony.yznaga@...cle.com>,
	Stanislav Kinsburskii <skinsburskii@...ux.microsoft.com>,
	<madvenka@...ux.microsoft.com>, <steven.sistare@...cle.com>,
	<yuleixzhang@...cent.com>
Subject: [RFC 17/18] pci: Don't clear bus master is persistence enabled

In order for persistent devices to continue to DMA during kexec the bus
mastering capability needs to remain on. Do not disable bus mastering if
pkernfs is enabled, indicating that persistent devices are enabled.

Only persistent devices should have bus mastering left on during kexec
but this serves as a rough approximation of the functionality needed for
this pkernfs RFC.
---
 drivers/pci/pci-driver.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
index 51ec9e7e784f..131127967811 100644
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -9,6 +9,7 @@
 #include <linux/init.h>
 #include <linux/device.h>
 #include <linux/mempolicy.h>
+#include <linux/pkernfs.h>
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <linux/sched.h>
@@ -519,7 +520,8 @@ static void pci_device_shutdown(struct device *dev)
 	 * If it is not a kexec reboot, firmware will hit the PCI
 	 * devices with big hammer and stop their DMA any way.
 	 */
-	if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
+	if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot)
+			&& !pkernfs_enabled())
 		pci_clear_master(pci_dev);
 }
 
-- 
2.40.1