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Re: [Xen-devel] [PATCH v5 05/10] domain: introduce XEN_DOMCTL_CDF_iommu flag



Hi Paul,

On 14/08/2019 14:38, Paul Durrant wrote:
This patch introduces a common domain creation flag to determine whether
the domain is permitted to make use of the IOMMU. Currently the flag is
always set (for both dom0 and domU) if the IOMMU is globally enabled
(i.e. iommu_enabled == 1). sanitise_domain_config() is modified to reject
the flag if !iommu_enabled.

A new helper function, is_iommu_enabled(), is added to test the flag and
iommu_domain_init() will return immediately if !is_iommu_enabled(). This is
slightly different to the previous behaviour based on !iommu_enabled where
the call to arch_iommu_domain_init() was made regardless, however it appears
that this call was only necessary to initialize the dt_devices list for ARM
such that iommu_release_dt_devices() can be called unconditionally by
domain_relinquish_resources(). Adding a simple check of is_iommu_enabled()
into iommu_release_dt_devices() keeps this unconditional call working.

No functional change should be observed with this patch applied.

Subsequent patches will allow the toolstack to control whether use of the
IOMMU is enabled for a domain.

NOTE: The introduction of the is_iommu_enabled() helper function might
       seem excessive but its use is expected to increase with subsequent
       patches. Also, having iommu_domain_init() bail before calling
       arch_iommu_domain_init() is not strictly necessary, but I think the
       consequent addition of the call to is_iommu_enabled() in
       iommu_release_dt_devices() makes the code clearer.

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

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

v5:
  - Move is_iommu_enabled() check into iommu_domain_init()
  - Reject XEN_DOMCTL_CDF_iommu in sanitise_domain_config() if !iommu_enabled
  - Use evaluate_nospec() in defintion of is_iommu_enabled()
---
  tools/libxl/libxl_create.c            | 8 ++++++++
  xen/arch/arm/domain.c                 | 1 -
  xen/arch/arm/setup.c                  | 3 +++
  xen/arch/x86/setup.c                  | 3 +++
  xen/common/domain.c                   | 9 ++++++++-
  xen/drivers/passthrough/device_tree.c | 3 +++
  xen/drivers/passthrough/iommu.c       | 6 +++---
  xen/include/public/domctl.h           | 4 ++++
  xen/include/xen/sched.h               | 5 +++++
  9 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 03ce166f4f..050ef042cd 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -555,6 +555,7 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config 
*d_config,
              .max_grant_frames = b_info->max_grant_frames,
              .max_maptrack_frames = b_info->max_maptrack_frames,
          };
+        libxl_physinfo physinfo;
if (info->type != LIBXL_DOMAIN_TYPE_PV) {
              create.flags |= XEN_DOMCTL_CDF_hvm_guest;
@@ -564,6 +565,13 @@ int libxl__domain_make(libxl__gc *gc, libxl_domain_config 
*d_config,
                  libxl_defbool_val(info->oos) ? 0 : XEN_DOMCTL_CDF_oos_off;
          }
+ rc = libxl_get_physinfo(ctx, &physinfo);
+        if (rc < 0)
+            goto out;
+
+        if (physinfo.cap_hvm_directio)
+            create.flags |= XEN_DOMCTL_CDF_iommu;

This is not going to work well on Arm as XEN_SYSCTL_PHYSCAP_directio is never 
set.

+
          /* 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/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 941bbff4fe..3ff19bc1ca 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -673,7 +673,6 @@ int arch_domain_create(struct domain *d,
ASSERT(config != NULL); - /* p2m_init relies on some value initialized by the IOMMU subsystem */

Even with this patch, I still think iommu_domain_init() is required before calling p2m_init(). For instance, this function will set the features flag.

      if ( (rc = iommu_domain_init(d)) != 0 )
          goto fail;

Cheers,

--
Julien Grall

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