[Xen-devel] [PATCH v6 10/10] introduce a 'passthrough' configuration option to xl.cfg...

[Paul Durrant <paul.durrant@citrix.com>]

...and hence the ability to disable IOMMU mappings, and control EPT
sharing.

This patch introduces a new 'libxl_passthrough' enumeration into
libxl_domain_create_info. The value will be set by xl either when it parses
a new 'passthrough' option in xl.cfg, or implicitly if there is passthrough
hardware specified for the domain.

If the value of the passthrough configuration option is 'disabled' then
the XEN_DOMCTL_CDF_iommu flag will be clear in the xen_domctl_createdomain
flags, thus allowing the toolstack to control whether the domain gets
IOMMU mappings or not (where previously they were globally set).

If the value of the passthrough configuration option is 'sync_pt' then
a new 'iommu_opts' field in xen_domctl_createdomain will be set with the
value XEN_DOMCTL_IOMMU_no_sharept. This will override the global default
set in iommu_hap_pt_share, thus allowing the toolstack to control whether
EPT sharing is used for the domain.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
---
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Wei Liu <wl@xen.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Julien Grall <julien.grall@arm.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Tim Deegan <tim@xen.org>
Cc: Anthony PERARD <anthony.perard@citrix.com>
Cc: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>

Previously part of series https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg02267.html

v6:
 - Remove the libxl_physinfo() call since it's usefulness is limited to x86

v5:
 - Expand xen_domctl_createdomain flags field and hence bump interface
   version
 - Fix spelling mistakes in context line
---
 docs/man/xl.cfg.5.pod.in        | 52 +++++++++++++++++++++++++++++++++
 tools/libxl/libxl.h             |  5 ++++
 tools/libxl/libxl_create.c      |  9 ++++++
 tools/libxl/libxl_types.idl     |  7 +++++
 tools/xl/xl_parse.c             | 38 ++++++++++++++++++++++++
 xen/arch/arm/domain.c           | 10 ++++++-
 xen/arch/x86/domain.c           |  2 +-
 xen/common/domain.c             |  7 +++++
 xen/drivers/passthrough/iommu.c | 13 ++++++++-
 xen/include/public/domctl.h     |  6 +++-
 xen/include/xen/iommu.h         | 19 ++++++++----
 11 files changed, 158 insertions(+), 10 deletions(-)

diff --git a/docs/man/xl.cfg.5.pod.in b/docs/man/xl.cfg.5.pod.in
index c99d40307e..fd35685e9e 100644
--- a/docs/man/xl.cfg.5.pod.in
+++ b/docs/man/xl.cfg.5.pod.in
@@ -605,6 +605,58 @@ option should only be used with a trusted device tree.
 Note that the partial device tree should avoid using the phandle 65000
 which is reserved by the toolstack.
 
+=item B<passthrough="STRING">
+
+Specify whether IOMMU mappings are enabled for the domain and hence whether
+it will be enabled for passthrough hardware. Valid values for this option
+are:
+
+=over 4
+
+=item B<disabled>
+
+IOMMU mappings are disabled for the domain and so hardware may not be
+passed through.
+
+This option is the default if no passthrough hardware is specified
+in the domain's configuration.
+
+=item B<sync_pt>
+
+This option means that IOMMU mappings will be synchronized with the
+domain's P2M table as follows:
+
+For a PV domain, all writable pages assigned to the domain are identity
+mapped by MFN in the IOMMU page table. Thus a device driver running in the
+domain may program passthrough hardware for DMA using MFN values
+(i.e. host/machine frame numbers) looked up in its P2M.
+
+For an HVM domain, all non-foreign RAM pages present in its P2M will be
+mapped by GFN in the IOMMU page table. Thus a device driver running in the
+domain may program passthrough hardware using GFN values (i.e. guest
+physical frame numbers) without any further translation.
+
+This option is the default if the domain is PV and passthrough hardware
+is specified in the configuration.
+
+This option is not available on Arm.
+
+=item B<share_pt>
+
+This option is unavailable for a PV domain. For an HVM domain, this option
+means that the IOMMU will be programmed to directly reference the domain's
+P2M table as its page table. From the point of view of a device driver
+running in the domain this is functionally equivalent to B<sync_pt> but
+places less load on the hypervisor and so should generally be selected in
+preference. However, the availability of this option is hardware specific
+and thus, if it is specified for a domain running on hardware that does
+not allow it (e.g. AMD), B<sync_pt> will be used instead.
+
+This option is the default if the domain is HVM and passthrough hardware
+is specified in the configuration.
+
+=back
+
 =back
 
 =head2 Devices
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index 9bacfb97f0..5de7c07a41 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -394,6 +394,11 @@
  */
 #define LIBXL_HAVE_EXTENDED_VKB 1
 
+/*
+ * libxl_domain_create_info has libxl_passthrough enumeration.
+ */
+#define LIBXL_HAVE_CREATEINFO_PASSTHROUGH 1
+
 /*
  * libxl ABI compatibility
  *
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 03ce166f4f..f288e13dc1 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -564,6 +564,15 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config *d_config,
                 libxl_defbool_val(info->oos) ? 0 : XEN_DOMCTL_CDF_oos_off;
         }
 
+        LOG(DETAIL, "passthrough: %s",
+            libxl_passthrough_to_string(info->passthrough));
+
+        if (info->passthrough != LIBXL_PASSTHROUGH_DISABLED)
+            create.flags |= XEN_DOMCTL_CDF_iommu;
+
+        if (info->passthrough == LIBXL_PASSTHROUGH_SYNC_PT)
+            create.iommu_opts |= XEN_DOMCTL_IOMMU_no_sharept;
+
         /* Ultimately, handle is an array of 16 uint8_t, same as uuid */
         libxl_uuid_copy(ctx, (libxl_uuid *)&create.handle, &info->uuid);
 
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index b61399ce36..7e37de8646 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -263,6 +263,12 @@ libxl_vkb_backend = Enumeration("vkb_backend", [
     (2, "LINUX")
     ])
 
+libxl_passthrough = Enumeration("passthrough", [
+    (0, "disabled"),
+    (1, "sync_pt"),
+    (2, "share_pt"),
+    ])
+
 #
 # Complex libxl types
 #
@@ -408,6 +414,7 @@ libxl_domain_create_info = Struct("domain_create_info",[
     ("pool_name",    string),
     ("run_hotplug_scripts",libxl_defbool),
     ("driver_domain",libxl_defbool),
+    ("passthrough",  libxl_passthrough),
     ], dir=DIR_IN)
 
 libxl_domain_restore_params = Struct("domain_restore_params", [
diff --git a/tools/xl/xl_parse.c b/tools/xl/xl_parse.c
index e105bda2bb..c904604008 100644
--- a/tools/xl/xl_parse.c
+++ b/tools/xl/xl_parse.c
@@ -2326,6 +2326,44 @@ skip_vfb:
         }
     }
 
+    if (!xlu_cfg_get_string(config, "passthrough", &buf, 0)) {
+        libxl_passthrough o;
+
+        e = libxl_passthrough_from_string(buf, &o);
+        if (e) {
+            fprintf(stderr,
+                    "ERROR: unknown passthrough option '%s'\n",
+                    buf);
+            exit(-ERROR_FAIL);
+        }
+
+        switch (o) {
+        case LIBXL_PASSTHROUGH_DISABLED:
+            if (d_config->num_pcidevs || d_config->num_dtdevs) {
+                fprintf(stderr,
+                        "ERROR: passthrough disabled but devices are specified\n");
+                exit(-ERROR_FAIL);
+            }
+        case LIBXL_PASSTHROUGH_SHARE_PT:
+            if (c_info->type == LIBXL_DOMAIN_TYPE_PV) {
+                fprintf(stderr,
+                        "ERROR: passthrough=\"share_pt\" not valid for PV domain\n");
+                exit(-ERROR_FAIL);
+            }
+        default:
+            break;
+        }
+
+        c_info->passthrough = o;
+    } else if (d_config->num_pcidevs || d_config->num_dtdevs) {
+        /*
+         * Passthrough devices are specified so set an appropriate
+         * default value.
+         */
+        c_info->passthrough = (c_info->type == LIBXL_DOMAIN_TYPE_PV) ?
+            LIBXL_PASSTHROUGH_SYNC_PT : LIBXL_PASSTHROUGH_SHARE_PT;
+    }
+
     if (!xlu_cfg_get_list(config, "usbctrl", &usbctrls, 0, 0)) {
         d_config->num_usbctrls = 0;
         d_config->usbctrls = NULL;
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 941bbff4fe..b12de6ff3d 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -614,6 +614,14 @@ int arch_sanitise_domain_config(struct xen_domctl_createdomain *config)
         return -EINVAL;
     }
 
+    /* Always share P2M Table between the CPU and the IOMMU */
+    if ( config->iommu_opts & XEN_DOMCTL_IOMMU_no_sharept )
+    {
+        dprintk(XENLOG_INFO,
+                "Unsupported iommu option: XEN_DOMCTL_IOMMU_no_sharept\n");
+        return -EINVAL;
+    }
+
     /* Fill in the native GIC version, passed back to the toolstack. */
     if ( config->arch.gic_version == XEN_DOMCTL_CONFIG_GIC_NATIVE )
     {
@@ -674,7 +682,7 @@ int arch_domain_create(struct domain *d,
     ASSERT(config != NULL);
 
     /* p2m_init relies on some value initialized by the IOMMU subsystem */
-    if ( (rc = iommu_domain_init(d)) != 0 )
+    if ( (rc = iommu_domain_init(d, config->iommu_opts)) != 0 )
         goto fail;
 
     if ( (rc = p2m_init(d)) != 0 )
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index f144d8fe9a..4f7dad49c5 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -604,7 +604,7 @@ int arch_domain_create(struct domain *d,
     if ( (rc = init_domain_irq_mapping(d)) != 0 )
         goto fail;
 
-    if ( (rc = iommu_domain_init(d)) != 0 )
+    if ( (rc = iommu_domain_init(d, config->iommu_opts)) != 0 )
         goto fail;
 
     psr_domain_init(d);
diff --git a/xen/common/domain.c b/xen/common/domain.c
index e832a5c4aa..142b08174b 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -308,6 +308,13 @@ static int sanitise_domain_config(struct xen_domctl_createdomain *config)
         return -EINVAL;
     }
 
+    if ( !(config->flags & XEN_DOMCTL_CDF_iommu) && config->iommu_opts )
+    {
+        dprintk(XENLOG_INFO,
+                "IOMMU options specified but IOMMU not enabled\n");
+        return -EINVAL;
+    }
+
     if ( config->max_vcpus < 1 )
     {
         dprintk(XENLOG_INFO, "No vCPUS\n");
diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index b24be5ffa6..a526aa6c09 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -159,7 +159,7 @@ static void __hwdom_init check_hwdom_reqs(struct domain *d)
     iommu_hwdom_strict = true;
 }
 
-int iommu_domain_init(struct domain *d)
+int iommu_domain_init(struct domain *d, unsigned int opts)
 {
     struct domain_iommu *hd = dom_iommu(d);
     int ret = 0;
@@ -176,6 +176,15 @@ int iommu_domain_init(struct domain *d)
     if ( ret )
         return ret;
 
+    /*
+     * Use shared page tables for HAP and IOMMU if the global option
+     * is enabled (from which we can infer the h/w is capable) and
+     * the domain options do not disallow it. HAP must, of course, also
+     * be enabled.
+     */
+    hd->hap_pt_share = hap_enabled(d) && iommu_hap_pt_share &&
+        !(opts & XEN_DOMCTL_IOMMU_no_sharept);
+
     /*
      * NB: 'relaxed' h/w domains don't need the IOMMU mappings to be kept
      *     in-sync with their assigned pages because all host RAM will be
@@ -187,6 +196,8 @@ int iommu_domain_init(struct domain *d)
     if ( !is_hardware_domain(d) || iommu_hwdom_strict )
         hd->need_sync = !iommu_use_hap_pt(d);
 
+    ASSERT(!(hd->need_sync && hd->hap_pt_share));
+
     return 0;
 }
 
diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h
index 3f82c78870..922ed50a11 100644
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -38,7 +38,7 @@
 #include "hvm/save.h"
 #include "memory.h"
 
-#define XEN_DOMCTL_INTERFACE_VERSION 0x00000011
+#define XEN_DOMCTL_INTERFACE_VERSION 0x00000012
 
 /*
  * NB. xen_domctl.domain is an IN/OUT parameter for this operation.
@@ -70,6 +70,10 @@ struct xen_domctl_createdomain {
 
     uint32_t flags;
 
+#define _XEN_DOMCTL_IOMMU_no_sharept  0
+#define XEN_DOMCTL_IOMMU_no_sharept   (1U<<_XEN_DOMCTL_IOMMU_no_sharept)
+    uint32_t iommu_opts;
+
     /*
      * Various domain limits, which impact the quantity of resources (global
      * mapping space, xenheap, etc) a guest may consume.
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 5e7ca98170..01025e372b 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -67,7 +67,7 @@ extern unsigned int iommu_dev_iotlb_timeout;
 int iommu_setup(void);
 int iommu_hardware_setup(void);
 
-int iommu_domain_init(struct domain *d);
+int iommu_domain_init(struct domain *d, unsigned int opts);
 void iommu_hwdom_init(struct domain *d);
 void iommu_domain_destroy(struct domain *d);
 
@@ -257,9 +257,17 @@ struct domain_iommu {
     DECLARE_BITMAP(features, IOMMU_FEAT_count);
 
     /*
-     * Does the guest reqire mappings to be synchonized, to maintain
-     * the default dfn == pfn map. (See comment on dfn at the top of
-     * include/xen/mm.h).
+     * Does the guest share HAP mapping with the IOMMU? This is always
+     * true for ARM systems and may be true for x86 systems where the
+     * the hardware is capable.
+     */
+    bool hap_pt_share;
+
+    /*
+     * Does the guest require mappings to be synchronized, to maintain
+     * the default dfn == pfn map? (See comment on dfn at the top of
+     * include/xen/mm.h). Note that hap_pt_share == false does not
+     * necessarily imply this is true.
      */
     bool need_sync;
 };
@@ -269,8 +277,7 @@ struct domain_iommu {
 #define iommu_clear_feature(d, f) clear_bit(f, dom_iommu(d)->features)
 
 /* Are we using the domain P2M table as its IOMMU pagetable? */
-#define iommu_use_hap_pt(d) \
-    (hap_enabled(d) && is_iommu_enabled(d) && iommu_hap_pt_share)
+#define iommu_use_hap_pt(d)       (dom_iommu(d)->hap_pt_share)
 
 /* Does the IOMMU pagetable need to be kept synchronized with the P2M */
 #ifdef CONFIG_HAS_PASSTHROUGH
-- 
2.20.1.2.gb21ebb671


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