[Xen-devel] [PATCH v2 4/4] xen/x86: Allow stubdom access to irq created for msi.

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

From: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>

Stubdomains need to be given sufficient privilege over the guest which it
provides emulation for in order for PCI passthrough to work correctly.
When a HVM domain try to enable MSI, QEMU in stubdomain calls
PHYSDEVOP_map_pirq, but later it needs to call XEN_DOMCTL_bind_pt_irq as
part of xc_domain_update_msi_irq. Allow for that as part of
PHYSDEVOP_map_pirq.

Based on 
https://github.com/OpenXT/xenclient-oe/blob/5e0e7304a5a3c75ef01240a1e3673665b2aaf05e/recipes-extended/xen/files/stubdomain-msi-irq-access.patch
 by Eric Chanudet <chanudete@xxxxxxxxxxxx>.

Signed-off-by: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
This is only one part of fixing MSI with QEMU in stubdomain. The other
part is allowing stubdomain to actually enable MSI in PCI config space.
QEMU does that through pcifront/back connected to the stubdomain (see
hw/xen/xen_pt_msi.c:msi_msix_enable()), but pciback by default refuse
write to that register.
Easy, less safe solution: enable permissive mode for the device.
Safer solution - enable access to this register for stubdomain only
(pciback patch that add such flag + libxl patch to set it for relevant
 devices)
The whole story:
https://www.qubes-os.org/news/2017/10/18/msi-support/

Any other ideas? Which one is preferred upstream?
---
 xen/arch/x86/irq.c     | 23 +++++++++++++++++++++++
 xen/arch/x86/physdev.c |  9 +++++++++
 2 files changed, 32 insertions(+)

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index 8b44d6c..123ca69 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2674,6 +2674,21 @@ int allocate_and_map_msi_pirq(struct domain *d, int 
index, int *pirq_p,
         {
     case MAP_PIRQ_TYPE_MULTI_MSI:
             irq = create_irq(NUMA_NO_NODE);
+            if ( !(irq < nr_irqs_gsi || irq >= nr_irqs) &&
+                 current->domain->target == d )
+            {
+                ret = irq_permit_access(current->domain, irq);
+                if ( ret ) {
+                    dprintk(XENLOG_G_ERR,
+                            "dom%d: can't grant it's stubdom (%d) access to "
+                            "irq %d for msi: %d!\n",
+                            d->domain_id,
+                            current->domain->domain_id,
+                            irq,
+                            ret);
+                    return -EINVAL;
+                }
+            }
         }
 
         if ( irq < nr_irqs_gsi || irq >= nr_irqs )
@@ -2717,7 +2732,15 @@ int allocate_and_map_msi_pirq(struct domain *d, int 
index, int *pirq_p,
         case MAP_PIRQ_TYPE_MSI:
             if ( index == -1 )
         case MAP_PIRQ_TYPE_MULTI_MSI:
+            {
+                if ( current->domain->target == d &&
+                     irq_deny_access(current->domain, irq) )
+                    dprintk(XENLOG_G_ERR,
+                            "dom%d: can't revoke stubdom's access to irq 
%d!\n",
+                            d->domain_id,
+                            irq);
                 destroy_irq(irq);
+            }
             break;
         }
     }
diff --git a/xen/arch/x86/physdev.c b/xen/arch/x86/physdev.c
index 3a3c158..de59e39 100644
--- a/xen/arch/x86/physdev.c
+++ b/xen/arch/x86/physdev.c
@@ -164,6 +164,15 @@ int physdev_unmap_pirq(domid_t domid, int pirq)
 
     pcidevs_lock();
     spin_lock(&d->event_lock);
+    if ( current->domain->target == d)
+    {
+        int irq = domain_pirq_to_irq(d, pirq);
+        if ( irq <= 0 || irq_deny_access(current->domain, irq) )
+            dprintk(XENLOG_G_ERR,
+                    "dom%d: can't revoke stubdom's access to irq %d!\n",
+                    d->domain_id,
+                    irq);
+    }
     ret = unmap_domain_pirq(d, pirq);
     spin_unlock(&d->event_lock);
     pcidevs_unlock();
-- 
git-series 0.9.1

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