[Xen-devel] [PATCH v1 09/10] xen/arm: Add use_iommu flag to xen_arch_domainconfig

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

This flag is intended to let Xen know that the guest has devices
which will most likely be used for passthrough and as the result
the use of IOMMU is expected for this domain.
The primary aim of this knowledge is to help the IOMMUs that don't
share page tables with the CPU on ARM be ready before P2M code starts
updating IOMMU mapping.
So, if this flag is set the non-shared IOMMUs will populate
their page tables at the domain creation time and thereby will be able
to handle IOMMU mapping updates from *the very beginning*.

In order to retain the current behavior for x86 still call
iommu_domain_init() with use_iommu flag being forced to false.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>

---
   Changes in V1:
      - Treat use_iommu flag as the ARM decision only. Don't use
        common domain creation flag for it, use ARM config instead.
      - Clarify patch subject/description.
---
 tools/libxl/libxl_arm.c       | 10 ++++++++++
 xen/arch/arm/domain.c         |  2 +-
 xen/include/public/arch-arm.h |  5 +++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/libxl/libxl_arm.c b/tools/libxl/libxl_arm.c
index d842d88..9c4705e 100644
--- a/tools/libxl/libxl_arm.c
+++ b/tools/libxl/libxl_arm.c
@@ -78,6 +78,16 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
         return ERROR_FAIL;
     }
 
+    /* TODO Are these assumptions enough to make decision about using IOMMU? */
+    if ((d_config->num_dtdevs && d_config->dtdevs) ||
+        (d_config->num_pcidevs && d_config->pcidevs))
+        xc_config->use_iommu = 1;
+    else
+        xc_config->use_iommu = 0;
+
+    LOG(DEBUG, "The use of IOMMU %s expected for this domain",
+        xc_config->use_iommu ? "is" : "isn't");
+
     return 0;
 }
 
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index ec19310..81c4b90 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -569,7 +569,7 @@ int arch_domain_create(struct domain *d, unsigned int 
domcr_flags,
     ASSERT(config != NULL);
 
     /* p2m_init relies on some value initialized by the IOMMU subsystem */
-    if ( (rc = iommu_domain_init(d, false)) != 0 )
+    if ( (rc = iommu_domain_init(d, config->use_iommu ? true : false)) != 0 )
         goto fail;
 
     if ( (rc = p2m_init(d)) != 0 )
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index bd974fb..cb33f75 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -322,6 +322,11 @@ struct xen_arch_domainconfig {
      *
      */
     uint32_t clock_frequency;
+    /*
+     * IN
+     * Inform the hypervisor that the use of IOMMU is expected for this domain.
+     */
+    uint8_t use_iommu;
 };
 #endif /* __XEN__ || __XEN_TOOLS__ */
 
-- 
2.7.4


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