Fix a limitation in bhyve that would limit the number of virtual machines to

the maximum number of VT-d domains (256 on a Sandybridge). We now allocate a
VT-d domain for a guest only if the administrator has explicitly configured
one or more PCI passthru device(s).

If there are no PCI passthru devices configured (the common case) then the
number of virtual machines is no longer limited by the maximum number of
VT-d domains.

Reviewed by: grehan@
Approved by: re@

3 files changed, 9 insertions, 1 deletions

diff --git a/sys/amd64/vmm/io/ppt.c b/sys/amd64/vmm/io/ppt.c
index 878bf8a..64d9ff5 100644
--- a/sys/amd64/vmm/io/ppt.c
+++ b/sys/amd64/vmm/io/ppt.c
@@ -592,3 +592,9 @@ ppt_setup_msix(struct vm *vm, int vcpu, int bus, int slot, int func,
 	return (0);
 }
 
+int
+ppt_num_devices(void)
+{
+
+	return (num_pptdevs);
+}
diff --git a/sys/amd64/vmm/io/ppt.h b/sys/amd64/vmm/io/ppt.h
index 63c8228..931893c 100644
--- a/sys/amd64/vmm/io/ppt.h
+++ b/sys/amd64/vmm/io/ppt.h
@@ -38,4 +38,5 @@ int	ppt_setup_msi(struct vm *vm, int vcpu, int bus, int slot, int func,
 		      int destcpu, int vector, int numvec);
 int	ppt_setup_msix(struct vm *vm, int vcpu, int bus, int slot, int func,
 		       int idx, uint32_t msg, uint32_t vector_control, uint64_t addr);
+int	ppt_num_devices(void);
 #endif
diff --git a/sys/amd64/vmm/vmm.c b/sys/amd64/vmm/vmm.c
index b4f3c33..5fc6b94 100644
--- a/sys/amd64/vmm/vmm.c
+++ b/sys/amd64/vmm/vmm.c
@@ -213,7 +213,8 @@ vmm_handler(module_t mod, int what, void *arg)
 	switch (what) {
 	case MOD_LOAD:
 		vmmdev_init();
-		iommu_init();
+		if (ppt_num_devices() > 0)
+			iommu_init();
 		error = vmm_init();
 		if (error == 0)
 			vmm_initialized = 1;