[Xen-devel] [PATCH] libxl: disallow PCI device assignment for HVM guest when PoD is enabled

[Wei Liu <wei.liu2@xxxxxxxxxx>]

This replicates a Xend behavior, see ec789523749 ("xend: Dis-allow
device assignment if PoD is enabled.").

This change is restricted to HVM guest, as only VT-d is relevant in the
counterpart in Xend. We're late in release cycle so the change should
only do what's necessary. Probably we can revisit it if we need to do
the same thing for PV guest in the future.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
Cc: Xiantao Zhang <xiantao.zhang@xxxxxxxxx>
---
 tools/libxl/libxl_create.c |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index e03bb55..b7adf34 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -706,6 +706,7 @@ static void initiate_domain_create(libxl__egc *egc,
     libxl_ctx *ctx = libxl__gc_owner(gc);
     uint32_t domid;
     int i, ret;
+    bool pod_enabled = false;
 
     /* convenience aliases */
     libxl_domain_config *const d_config = dcs->guest_config;
@@ -714,6 +715,27 @@ static void initiate_domain_create(libxl__egc *egc,
 
     domid = 0;
 
+    /* If target_memkb is smaller than max_memkb, the subsequent call
+     * to libxc when building HVM domain will enable PoD mode.
+     */
+    pod_enabled = (d_config->c_info.type == LIBXL_DOMAIN_TYPE_HVM) &&
+        (d_config->b_info.target_memkb < d_config->b_info.max_memkb);
+
+    /* We cannot have PoD and PCI device assignment at the same time
+     * for HVM guest. It was reported that VT-d engine cannot
+     * work with PoD enabled because it needs to populated entire page
+     * table for guest. Also a quick grep through AMD IOMMU related
+     * code suggests it has not coped with PoD as well. Just to stay
+     * on the safe side, we disable PCI device assignment with PoD all
+     * together, regardless of the underlying IOMMU in use.
+     */
+    if (d_config->c_info.type == LIBXL_DOMAIN_TYPE_HVM &&
+        d_config->num_pcidevs && pod_enabled) {
+        ret = ERROR_INVAL;
+        LOG(ERROR, "PCI device assignment for HVM guest failed due to PoD 
enabled");
+        goto error_out;
+    }
+
     ret = libxl__domain_create_info_setdefault(gc, &d_config->c_info);
     if (ret) goto error_out;
 
-- 
1.7.10.4


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