[Xen-devel] [PATCH v3 1/2] xen/pt: fix some pass-thru devices don't work across reboot

[Chao Gao <chao.gao@xxxxxxxxx>]

I find some pass-thru devices don't work any more across guest
reboot. Assigning it to another domain also meets the same issue. And
the only way to make it work again is un-binding and binding it to
pciback. Someone reported this issue one year ago [1].

If the device's driver doesn't disable MSI-X during shutdown or qemu is
killed/crashed before the domain shutdown, this domain's pirq won't be
unmapped. Then xen takes over this work, unmapping all pirq-s, when
destroying guest. But as pciback has already disabled meory decoding before
xen unmapping pirq, Xen has to sets the host_maskall flag and maskall bit
to mask a MSI rather than sets maskbit in MSI-x table. The call trace of
this process is:

->arch_domain_destroy
    ->free_domain_pirqs
        ->unmap_domain_pirq (if pirq isn't unmapped by qemu)
            ->pirq_guest_force_unbind
                ->__pirq_guest_unbind
                    ->mask_msi_irq(=desc->handler->disable())
                        ->the warning in msi_set_mask_bit()

The host_maskall bit will prevent guests from clearing the maskall bit
even the device is assigned to another guest later. Then guests cannot
receive MSIs from this device.

To fix this issue, a pirq is unmapped before memory decoding is disabled by
pciback. Specifically, when a device is detached from a guest, all established
mappings between pirq and msi are destroying before changing the ownership.

[1]: https://lists.xenproject.org/archives/html/xen-devel/2017-09/msg02520.html

Signed-off-by: Chao Gao <chao.gao@xxxxxxxxx>
---
Applied this patch, qemu would report the error below:
    [00:05.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1, 
pirq: 302, gvec: 0xd5)
    [00:05.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1, 
pirq: 301, gvec: 0xe5)
    [00:04.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1, 
pirq: 359, gvec: 0x41)
    [00:04.0] msi_msix_disable: Error: Unbinding of MSI-X failed. (err: 1, 
pirq: 358, gvec: 0x51)

Despite of the error, guest shutdown or device hotplug finishs smoothly.
It seems to me that qemu tries to unbind a msi which is already unbound by
the code added by this patch. I am not sure whether it is acceptable to
leave this error there.
---
 xen/drivers/passthrough/io.c  | 57 +++++++++++++++++++++++++++++--------------
 xen/drivers/passthrough/pci.c | 49 +++++++++++++++++++++++++++++++++++++
 xen/include/xen/iommu.h       |  1 +
 3 files changed, 89 insertions(+), 18 deletions(-)

diff --git a/xen/drivers/passthrough/io.c b/xen/drivers/passthrough/io.c
index a6eb8a4..56ee1ef 100644
--- a/xen/drivers/passthrough/io.c
+++ b/xen/drivers/passthrough/io.c
@@ -619,6 +619,42 @@ int pt_irq_create_bind(
     return 0;
 }
 
+static void pt_irq_destroy_bind_common(struct domain *d, struct pirq *pirq)
+{
+    struct hvm_pirq_dpci *pirq_dpci = pirq_dpci(pirq);
+
+    ASSERT(spin_is_locked(&d->event_lock));
+
+    if ( pirq_dpci && (pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) &&
+         list_empty(&pirq_dpci->digl_list) )
+    {
+        pirq_guest_unbind(d, pirq);
+        msixtbl_pt_unregister(d, pirq);
+        if ( pt_irq_need_timer(pirq_dpci->flags) )
+            kill_timer(&pirq_dpci->timer);
+        pirq_dpci->flags = 0;
+        /*
+         * See comment in pt_irq_create_bind's PT_IRQ_TYPE_MSI before the
+         * call to pt_pirq_softirq_reset.
+         */
+        pt_pirq_softirq_reset(pirq_dpci);
+
+        pirq_cleanup_check(pirq, d);
+    }
+}
+
+void pt_irq_destroy_bind_msi(struct domain *d, struct pirq *pirq)
+{
+    struct hvm_pirq_dpci *pirq_dpci = pirq_dpci(pirq);
+
+    ASSERT(spin_is_locked(&d->event_lock));
+
+    if ( pirq_dpci && pirq_dpci->gmsi.posted )
+        pi_update_irte(NULL, pirq, 0);
+
+    pt_irq_destroy_bind_common(d, pirq);
+}
+
 int pt_irq_destroy_bind(
     struct domain *d, const struct xen_domctl_bind_pt_irq *pt_irq_bind)
 {
@@ -727,26 +763,11 @@ int pt_irq_destroy_bind(
         }
         else
             what = "bogus";
-    }
-    else if ( pirq_dpci && pirq_dpci->gmsi.posted )
-        pi_update_irte(NULL, pirq, 0);
-
-    if ( pirq_dpci && (pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) &&
-         list_empty(&pirq_dpci->digl_list) )
-    {
-        pirq_guest_unbind(d, pirq);
-        msixtbl_pt_unregister(d, pirq);
-        if ( pt_irq_need_timer(pirq_dpci->flags) )
-            kill_timer(&pirq_dpci->timer);
-        pirq_dpci->flags = 0;
-        /*
-         * See comment in pt_irq_create_bind's PT_IRQ_TYPE_MSI before the
-         * call to pt_pirq_softirq_reset.
-         */
-        pt_pirq_softirq_reset(pirq_dpci);
 
-        pirq_cleanup_check(pirq, d);
+        pt_irq_destroy_bind_common(d, pirq);
     }
+    else
+        pt_irq_destroy_bind_msi(d, pirq);
 
     spin_unlock(&d->event_lock);
 
diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 1277ce2..88a8007 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -368,6 +368,7 @@ static struct pci_dev *alloc_pdev(struct pci_seg *pseg, u8 
bus, u8 devfn)
             return NULL;
         }
         spin_lock_init(&msix->table_lock);
+        msix->warned = DOMID_INVALID;
         pdev->msix = msix;
     }
 
@@ -1514,6 +1515,52 @@ static int assign_device(struct domain *d, u16 seg, u8 
bus, u8 devfn, u32 flag)
     return rc;
 }
 
+/*
+ * Unmap established mappings between domain's pirq and device's MSI.
+ * These mappings were set up by qemu/guest and are expected to be
+ * destroyed when changing the device's ownership.
+ */
+static void pci_unmap_msi(struct pci_dev *pdev)
+{
+    struct msi_desc *entry, *tmp;
+
+    ASSERT(pcidevs_locked());
+
+    if ( !pdev->domain )
+        return;
+
+    spin_lock(&pdev->domain->event_lock);
+    list_for_each_entry_safe( entry, tmp, &pdev->msi_list, list )
+    {
+        struct pirq *info;
+        struct hvm_pirq_dpci *pirq_dpci;
+        int pirq = domain_irq_to_pirq(pdev->domain, entry->irq), pirq_orig;
+
+        pirq_orig = pirq;
+
+        if ( !pirq )
+            continue;
+
+        /* For forcibly unmapped pirq, lookup radix tree with absolute value */
+        if ( pirq < 0)
+            pirq = -pirq;
+
+        info = pirq_info(pdev->domain, pirq);
+        if ( !info )
+            continue;
+        pirq_dpci = pirq_dpci(info);
+
+        if ( pirq_dpci &&
+             (pirq_dpci->flags & HVM_IRQ_DPCI_MACH_MSI) &&
+             (pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI) )
+            pt_irq_destroy_bind_msi(pdev->domain, info);
+
+        if ( pirq_orig > 0 )
+            unmap_domain_pirq(pdev->domain, pirq_orig);
+    }
+    spin_unlock(&pdev->domain->event_lock);
+}
+
 /* caller should hold the pcidevs_lock */
 int deassign_device(struct domain *d, u16 seg, u8 bus, u8 devfn)
 {
@@ -1529,6 +1576,8 @@ int deassign_device(struct domain *d, u16 seg, u8 bus, u8 
devfn)
     if ( !pdev )
         return -ENODEV;
 
+    pci_unmap_msi(pdev);
+
     while ( pdev->phantom_stride )
     {
         devfn += pdev->phantom_stride;
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 3d78126..8aecf43 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -108,6 +108,7 @@ struct pirq;
 int hvm_do_IRQ_dpci(struct domain *, struct pirq *);
 int pt_irq_create_bind(struct domain *, const struct xen_domctl_bind_pt_irq *);
 int pt_irq_destroy_bind(struct domain *, const struct xen_domctl_bind_pt_irq 
*);
+void pt_irq_destroy_bind_msi(struct domain *d, struct pirq *pirq);
 
 void hvm_dpci_isairq_eoi(struct domain *d, unsigned int isairq);
 struct hvm_irq_dpci *domain_get_irq_dpci(const struct domain *);
-- 
1.8.3.1


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