[Xen-devel] [PATCH] xl, libxl: Add per-device and global permissive config options for pci passthrough

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

By default pciback only allows PV guests to write "known safe" values into
PCI config space.  But many devices require writes to other areas of config
space in order to operate properly.  One way to do that is with the "quirks"
interface, which specifies areas known safe to a particular device; the
other way is to mark a device as "permissive", which tells pciback to allow
all config space writes for that domain and device.

This adds a "permissive" flag to the libxl_pci struct and teaches libxl how
to write the appropriate value into sysfs to enable the permissive feature for
devices being passed through.  It also adds the permissive config options either
on a per-device basis, or as a global option in the xl command-line.

Because of the potential stability and security implications of enabling
permissive, the flag is left off by default.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

diff -r f744e82ea740 -r 980c34bd5e51 docs/man/xl.cfg.pod.5
--- a/docs/man/xl.cfg.pod.5     Wed Feb 29 16:30:34 2012 +0000
+++ b/docs/man/xl.cfg.pod.5     Tue Mar 27 18:02:41 2012 +0100
@@ -294,10 +294,25 @@ XXX
 
 XXX
 
+=item B<permissive=BOOLEAN>
+
+By default pciback only allows PV guests to write "known safe" values into
+PCI config space.  But many devices require writes to other areas of config
+space in order to operate properly.  This tells the pciback driver to
+allow all writes to PCI config space for this domain and this device.  This
+option should be enabled with caution, as there may be stability or security 
+implications of doing so.
+
 =back
 
 =back
 
+=item B<pci_permissive=BOOLEAN>
+
+Changes the default value of 'permissive' for all PCI devices for this
+VM.  This can still be overriden on a per-device basis. See the
+"pci=" section for more information on the "permissive" flag.
+
 =back
 
 =head2 Paravirtualised (PV) Guest Specific Options
diff -r f744e82ea740 -r 980c34bd5e51 tools/libxl/libxl_pci.c
--- a/tools/libxl/libxl_pci.c   Wed Feb 29 16:30:34 2012 +0000
+++ b/tools/libxl/libxl_pci.c   Tue Mar 27 18:02:41 2012 +0100
@@ -165,6 +165,8 @@ int libxl_device_pci_parse_bdf(libxl_ctx
                     pcidev->msitranslate = atoi(tok);
                 }else if ( !strcmp(optkey, "power_mgmt") ) {
                     pcidev->power_mgmt = atoi(tok);
+                }else if ( !strcmp(optkey, "permissive") ) {
+                    pcidev->permissive = atoi(tok);
                 }else{
                     LIBXL__LOG(ctx, LIBXL__LOG_WARNING,
                            "Unknown PCI BDF option: %s", optkey);
@@ -198,7 +200,10 @@ static void libxl_create_pci_backend_dev
     if (pcidev->vdevfn)
         flexarray_append_pair(back, libxl__sprintf(gc, "vdevfn-%d", num), 
libxl__sprintf(gc, "%x", pcidev->vdevfn));
     flexarray_append(back, libxl__sprintf(gc, "opts-%d", num));
-    flexarray_append(back, libxl__sprintf(gc, "msitranslate=%d,power_mgmt=%d", 
pcidev->msitranslate, pcidev->power_mgmt));
+    flexarray_append(back,
+              libxl__sprintf(gc, "msitranslate=%d,power_mgmt=%d,permissive=%d",
+                             pcidev->msitranslate, pcidev->power_mgmt,
+                             pcidev->permissive));
     flexarray_append_pair(back, libxl__sprintf(gc, "state-%d", num), 
libxl__sprintf(gc, "%d", 1));
 }
 
@@ -708,6 +713,20 @@ static int do_pci_add(libxl__gc *gc, uin
             }
         }
         fclose(f);
+
+        /* Don't restrict writes to the PCI config space from this VM */
+        if(pcidev->permissive) {
+            sysfs_path = libxl__sprintf(gc, SYSFS_PCIBACK_DRIVER"/permissive");
+            f = fopen(sysfs_path, "w");
+            if (f == NULL) {
+                LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "Couldn't open %s",
+                                 sysfs_path);
+                goto out;
+            }
+            fprintf(f, PCI_BDF, pcidev->domain, pcidev->bus,
+                    pcidev->dev, pcidev->func);
+            fclose(f);
+        }
         break;
     }
     default:
@@ -1101,6 +1120,9 @@ static void libxl__device_pci_from_xs_be
             } else if (!strcmp(p, "power_mgmt")) {
                 p = strtok_r(NULL, ",=", &saveptr);
                 pci->power_mgmt = atoi(p);
+            } else if (!strcmp(p, "permissive")) {
+                p = strtok_r(NULL, ",=", &saveptr);
+                pci->permissive = atoi(p);
             }
         } while ((p = strtok_r(NULL, ",=", &saveptr)) != NULL);
     }
diff -r f744e82ea740 -r 980c34bd5e51 tools/libxl/libxl_types.idl
--- a/tools/libxl/libxl_types.idl       Wed Feb 29 16:30:34 2012 +0000
+++ b/tools/libxl/libxl_types.idl       Tue Mar 27 18:02:41 2012 +0100
@@ -352,6 +352,7 @@ libxl_device_pci = Struct("device_pci", 
     ("vfunc_mask", uint32),
     ("msitranslate", bool),
     ("power_mgmt", bool),
+    ("permissive", bool),
     ])
 
 libxl_diskinfo = Struct("diskinfo", [
diff -r f744e82ea740 -r 980c34bd5e51 tools/libxl/xl_cmdimpl.c
--- a/tools/libxl/xl_cmdimpl.c  Wed Feb 29 16:30:34 2012 +0000
+++ b/tools/libxl/xl_cmdimpl.c  Tue Mar 27 18:02:41 2012 +0100
@@ -518,6 +518,7 @@ static void parse_config_data(const char
     XLU_ConfigList *cpus, *vbds, *nics, *pcis, *cvfbs, *cpuids;
     int pci_power_mgmt = 0;
     int pci_msitranslate = 1;
+    int pci_permissive = 0;
     int e;
 
     libxl_domain_create_info *c_info = &d_config->c_info;
@@ -986,6 +987,9 @@ skip_vfb:
     if (!xlu_cfg_get_long (config, "pci_power_mgmt", &l, 0))
         pci_power_mgmt = l;
 
+    if (!xlu_cfg_get_long (config, "pci_permissive", &l, 0))
+        pci_permissive = l;
+
     /* To be reworked (automatically enabled) once the auto ballooning
      * after guest starts is done (with PCI devices passed in). */
     if (c_info->type == LIBXL_DOMAIN_TYPE_PV) {
@@ -1005,6 +1009,7 @@ skip_vfb:
 
             pcidev->msitranslate = pci_msitranslate;
             pcidev->power_mgmt = pci_power_mgmt;
+            pcidev->permissive = pci_permissive;
             if (!libxl_device_pci_parse_bdf(ctx, pcidev, buf))
                 d_config->num_pcidevs++;
         }
diff -r f744e82ea740 -r 980c34bd5e51 tools/libxl/xl_sxp.c
--- a/tools/libxl/xl_sxp.c      Wed Feb 29 16:30:34 2012 +0000
+++ b/tools/libxl/xl_sxp.c      Tue Mar 27 18:02:41 2012 +0100
@@ -199,9 +199,10 @@ void printf_info_sexp(int domid, libxl_d
                d_config->pcidevs[i].domain, d_config->pcidevs[i].bus,
                d_config->pcidevs[i].dev, d_config->pcidevs[i].func,
                d_config->pcidevs[i].vdevfn);
-        printf("\t\t\t(opts msitranslate %d power_mgmt %d)\n",
+        printf("\t\t\t(opts msitranslate %d power_mgmt %d permissive %d)\n",
                d_config->pcidevs[i].msitranslate,
-               d_config->pcidevs[i].power_mgmt);
+               d_config->pcidevs[i].power_mgmt,
+               d_config->pcidevs[i].permissive);
         printf("\t\t)\n");
         printf("\t)\n");
     }

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