linux-kernel - Re: [PATCH] iommu/vt-d: Flush old iotlb for kdump when the device gets context mapped

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Date:   Thu, 1 Dec 2016 10:15:45 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     Joerg Roedel <joro@...tes.org>, Baoquan He <bhe@...hat.com>
Cc:     xlpang@...hat.com, Don Brace <don.brace@...rosemi.com>,
        Myron Stowe <myron.stowe@...hat.com>,
        kexec@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org,
        Myron Stowe <myron.stowe@...il.com>,
        Dave Young <dyoung@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] iommu/vt-d: Flush old iotlb for kdump when the device
 gets context mapped

On 11/30/2016 at 10:26 PM, Joerg Roedel wrote:
> On Wed, Nov 30, 2016 at 06:23:34PM +0800, Baoquan He wrote:
>> OK, talked with Xunlei. The old cache could be entry with present bit
>> set.
> -EPARSE
>
> Anyway, what I was trying to say is, that the IOMMU TLB is tagged with
> domain-ids, and that there is also a context-cache which maps device-ids
> to domain-ids.
>
> If we update the context entry then we need to flush only the context
> entry, as it will point to a new domain-id then and future IOTLB lookups
> in the IOMMU will be using the new domain-id and do not match the old
> entries.

Hi Joerg,

Thanks for the explanation, and we still need to flush context cache using old domain-id, right?
How about the following update?

index 3965e73..624eac9 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2024,6 +2024,25 @@ static int domain_context_mapping_one(struct dmar_domain *domain,
        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;