Patch "iommu/vt-d: Flush old iommu caches for kdump when the device gets context mapped" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

iommu/vt-d: Flush old iommu caches for kdump when the device gets context mapped

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iommu-vt-d-flush-old-iommu-caches-for-kdump-when-the-device-gets-context-mapped.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Xunlei Pang <[email protected]>
Date: Mon, 5 Dec 2016 20:09:07 +0800
Subject: iommu/vt-d: Flush old iommu caches for kdump when the device gets context mapped

From: Xunlei Pang <[email protected]>

commit aec0e86172a79eb5e44aff1055bb953fe4d47c59 upstream.

We met the DMAR fault both on hpsa P420i and P421 SmartArray controllers
under kdump, it can be steadily reproduced on several different machines,
the dmesg log is like:
HP HPSA Driver (v 3.4.16-0)
hpsa 0000:02:00.0: using doorbell to reset controller
hpsa 0000:02:00.0: board ready after hard reset.
hpsa 0000:02:00.0: Waiting for controller to respond to no-op
DMAR: Setting identity map for device 0000:02:00.0 [0xe8000 - 0xe8fff]
DMAR: Setting identity map for device 0000:02:00.0 [0xf4000 - 0xf4fff]
DMAR: Setting identity map for device 0000:02:00.0 [0xbdf6e000 - 0xbdf6efff]
DMAR: Setting identity map for device 0000:02:00.0 [0xbdf6f000 - 0xbdf7efff]
DMAR: Setting identity map for device 0000:02:00.0 [0xbdf7f000 - 0xbdf82fff]
DMAR: Setting identity map for device 0000:02:00.0 [0xbdf83000 - 0xbdf84fff]
DMAR: DRHD: handling fault status reg 2
DMAR: [DMA Read] Request device [02:00.0] fault addr fffff000 [fault reason 06] PTE Read access is not set hpsa 0000:02:00.0: controller message 03:00 timed out
hpsa 0000:02:00.0: no-op failed; re-trying

After some debugging, we found that the fault addr is from DMA initiated at the driver probe stage after reset(not in-flight DMA), and the corresponding pte entry value is correct, the fault is likely due to the old iommu caches of the in-flight DMA before it.

Thus we need to flush the old cache after context mapping is setup for the device, where the device is supposed to finish reset at its driver probe stage and no in-flight DMA exists hereafter.

I'm not sure if the hardware is responsible for invalidating all the related caches allocated in the iommu hardware before, but seems not the case for hpsa, actually many device drivers have problems in properly resetting the hardware. Anyway flushing (again) by software in kdump kernel when the device gets context mapped which is a quite infrequent operation does little harm.

With this patch, the problematic machine can survive the kdump tests.

---
 drivers/iommu/intel-iommu.c |   19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

@@ -2037,6 +2037,25 @@ static int domain_context_mapping_one(st
 	if (context_present(context))
 		goto out_unlock;
 
+	/*
+	 * For kdump cases, old valid entries may be cached due to the
+	 * in-flight DMA and copied pgtable, but there is no unmapping
+	 * behaviour for them, thus we need an explicit cache flush for
+	 * the newly-mapped device. For kdump, at this point, the device
+	 * is supposed to finish reset at its driver probe stage, so no
+	 * in-flight DMA will exist, and we don't need to worry anymore
+	 * hereafter.
+	 */
+	if (context_copied(context)) {
+		u16 did_old = context_domain_id(context);
+
+		if (did_old >= 0 && did_old < cap_ndoms(iommu->cap))
+			iommu->flush.flush_context(iommu, did_old,
+						   (((u16)bus) << 8) | devfn,
+						   DMA_CCMD_MASK_NOBIT,
+						   DMA_CCMD_DEVICE_INVL);
+	}
+
 	pgd = domain->pgd;
 
 	context_clear_entry(context);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/iommu-vt-d-flush-old-iommu-caches-for-kdump-when-the-device-gets-context-mapped.patch