[Xen-devel] [PATCH 2 of 2] xl, libxl: Add per-device and global permissive config options for pci passthrough

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

# HG changeset patch
# User George Dunlap <george.dunlap@xxxxxxxxxxxxx>
# Date 1333363500 -3600
# Node ID 62b1030a2485536caf995b825bee9e8255f914b3
# Parent  5386937e6c5c9afaa8a3cd56d391dcc9e40d0596
xl,libxl: Add per-device and global permissive config options for pci 
passthrough

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 5386937e6c5c -r 62b1030a2485 docs/man/xl.cfg.pod.5
--- a/docs/man/xl.cfg.pod.5     Mon Apr 02 11:29:34 2012 +0100
+++ b/docs/man/xl.cfg.pod.5     Mon Apr 02 11:45:00 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 5386937e6c5c -r 62b1030a2485 tools/libxl/libxl_pci.c
--- a/tools/libxl/libxl_pci.c   Mon Apr 02 11:29:34 2012 +0100
+++ b/tools/libxl/libxl_pci.c   Mon Apr 02 11:45:00 2012 +0100
@@ -55,7 +55,10 @@ 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));
 }
 
@@ -565,6 +568,29 @@ 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) {
+            int fd;
+            char *buf;
+
+            sysfs_path = libxl__sprintf(gc, SYSFS_PCIBACK_DRIVER"/permissive");
+            fd = open(sysfs_path, O_WRONLY);
+            if (fd < 0) {
+                LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "Couldn't open %s",
+                                 sysfs_path);
+                goto out;
+            }
+ 
+            buf = libxl__sprintf(gc, PCI_BDF, pcidev->domain, pcidev->bus,
+                                 pcidev->dev, pcidev->func);
+            rc = write(fd, buf, strlen(buf));
+            if (rc < 0)
+                LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR, "write to %s returned 
%d",
+                                 sysfs_path, rc);
+            close(fd);
+            goto out;
+        }
         break;
     }
     default:
@@ -958,6 +984,9 @@ 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 5386937e6c5c -r 62b1030a2485 tools/libxl/libxl_types.idl
--- a/tools/libxl/libxl_types.idl       Mon Apr 02 11:29:34 2012 +0100
+++ b/tools/libxl/libxl_types.idl       Mon Apr 02 11:45:00 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 5386937e6c5c -r 62b1030a2485 tools/libxl/libxlu_pci.c
--- a/tools/libxl/libxlu_pci.c  Mon Apr 02 11:29:34 2012 +0100
+++ b/tools/libxl/libxlu_pci.c  Mon Apr 02 11:45:00 2012 +0100
@@ -127,6 +127,8 @@ int xlu_pci_parse_bdf(XLU_Config *cfg, l
                     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{
                     XLU__PCI_ERR(cfg, "Unknown PCI BDF option: %s", optkey);
                 }
diff -r 5386937e6c5c -r 62b1030a2485 tools/libxl/xl_cmdimpl.c
--- a/tools/libxl/xl_cmdimpl.c  Mon Apr 02 11:29:34 2012 +0100
+++ b/tools/libxl/xl_cmdimpl.c  Mon Apr 02 11:45:00 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 (!xlu_pci_parse_bdf(config, pcidev, buf))
                 d_config->num_pcidevs++;
         }

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