[PATCH v8 4/4] xen/arm: grant: Add another entry to map MFN 1:1 in dom0 p2m

[Julien Grall <julien.grall@linaro.org>]

Grant mapping can be used for DMA request. The dev_bus_addr returned by the
hypercall is the MFN (not the IPA). Currently Linux is using this address (via
swiotlb) to program the DMA.
When the device is protected by IOMMU the request will fail. We have to
add 1:1 mapping in the domain p2m to allow DMA request working.

This is valid because DOM0 has its memory mapped 1:1 and therefore we know
that RAM and devices cannot clash.

The grant mapping code already handle this case for x86 PV guests. Reuse the
same code path for ARM guest.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Cc: Jan Beulich <jbeulich@suse.com>

---
    The patch has been heavily rework to use iommu_{,un}map_page. I dropped
    all the acks.

    Changes in v8:
        - Rework differently the 1:1 mapping by using iommu_{,un}map_page
        helpers.

    Changes in v5:
        - Update commit message

    Changes in v4:
        - Patch added
---
 xen/arch/arm/p2m.c                 |    2 ++
 xen/common/grant_table.c           |    4 ++--
 xen/drivers/passthrough/arm/smmu.c |   44 ++++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/grant_table.h  |    2 ++
 xen/include/asm-arm/p2m.h          |    2 ++
 xen/include/asm-x86/grant_table.h  |    2 ++
 6 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 96bc0ef..810459a 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -227,6 +227,7 @@ static lpae_t mfn_to_p2m_entry(unsigned long mfn, unsigned int mattr,
         e.p2m.write = 0;
         break;
 
+    case p2m_iommu_map_rw:
     case p2m_map_foreign:
     case p2m_grant_map_rw:
     case p2m_mmio_direct:
@@ -234,6 +235,7 @@ static lpae_t mfn_to_p2m_entry(unsigned long mfn, unsigned int mattr,
         e.p2m.write = 1;
         break;
 
+    case p2m_iommu_map_ro:
     case p2m_grant_map_ro:
     case p2m_invalid:
         e.p2m.xn = 1;
diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index 2c93d9c..7e549f2 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -727,7 +727,7 @@ __gnttab_map_grant_ref(
 
     double_gt_lock(lgt, rgt);
 
-    if ( !paging_mode_translate(ld) && need_iommu(ld) )
+    if ( gnttab_need_iommu_mapping(ld) && need_iommu(ld) )
     {
         unsigned int wrc, rdc;
         int err = 0;
@@ -935,7 +935,7 @@ __gnttab_unmap_common(
             act->pin -= GNTPIN_hstw_inc;
     }
 
-    if ( !paging_mode_translate(ld) && need_iommu(ld) )
+    if ( gnttab_need_iommu_mapping(ld) && need_iommu(ld) )
     {
         unsigned int wrc, rdc;
         int err = 0;
diff --git a/xen/drivers/passthrough/arm/smmu.c b/xen/drivers/passthrough/arm/smmu.c
index 21b4572..9f85800 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -1536,6 +1536,48 @@ static void arm_smmu_iommu_domain_teardown(struct domain *d)
     xfree(smmu_domain);
 }
 
+static int arm_smmu_map_page(struct domain *d, unsigned long gfn,
+                             unsigned long mfn, unsigned int flags)
+{
+    p2m_type_t t;
+
+    /* This function should only be used by gnttab code when the domain
+     * is direct mapped and gfn == mfn.
+     */
+    if ( !is_domain_direct_mapped(d) || gfn != mfn )
+        return -EINVAL;
+
+    /* We only support readable and writable flags */
+    if ( !(flags & (IOMMUF_readable | IOMMUF_writable)) )
+        return -EINVAL;
+
+    /* The function guest_physmap_add_entry replace the current mapping
+     * if there is already one...
+     */
+    t = (flags & IOMMUF_writable)? p2m_iommu_map_rw : p2m_iommu_map_ro;
+
+    /* Grant mapping can be used for DMA request. The dev_bus_addr returned by
+     * the hypercall is the MFN (not the IPA). For device protected by
+     * an IOMMU, Xen needs to add a 1:1 mapping in the domain p2m to
+     * allow DMA request working.
+     * This is only valid when the domain is directed mapped
+     */
+    return guest_physmap_add_entry(d, gfn, mfn, 0, t);
+}
+
+static int arm_smmu_unmap_page(struct domain *d, unsigned long gfn)
+{
+    /* This function should only be used by gnttab code when the domain
+     * is direct mapped
+     */
+    if ( !is_domain_direct_mapped(d) )
+        return -EINVAL;
+
+    guest_physmap_remove_page(d, gfn, gfn, 0);
+
+    return 0;
+}
+
 static const struct iommu_ops arm_smmu_iommu_ops = {
     .init = arm_smmu_iommu_domain_init,
     .hwdom_init = arm_smmu_iommu_hwdom_init,
@@ -1544,6 +1586,8 @@ static const struct iommu_ops arm_smmu_iommu_ops = {
     .iotlb_flush_all = arm_smmu_iotlb_flush_all,
     .assign_dt_device = arm_smmu_attach_dev,
     .reassign_dt_device = arm_smmu_reassign_dt_dev,
+    .map_page = arm_smmu_map_page,
+    .unmap_page = arm_smmu_unmap_page,
 };
 
 static int __init smmu_init(struct dt_device_node *dev,
diff --git a/xen/include/asm-arm/grant_table.h b/xen/include/asm-arm/grant_table.h
index 6e0cc59..673bcdd 100644
--- a/xen/include/asm-arm/grant_table.h
+++ b/xen/include/asm-arm/grant_table.h
@@ -33,6 +33,8 @@ static inline int replace_grant_supported(void)
     ( ((i >= nr_grant_frames(d->grant_table)) &&                         \
      (i < max_nr_grant_frames)) ? 0 : (d->arch.grant_table_gpfn[i]))
 
+#define gnttab_need_iommu_mapping(d)    is_domain_direct_mapped(d)
+
 #endif /* __ASM_GRANT_TABLE_H__ */
 /*
  * Local variables:
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index bd71abe..b68d5b8 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -45,6 +45,8 @@ typedef enum {
     p2m_map_foreign,    /* Ram pages from foreign domain */
     p2m_grant_map_rw,   /* Read/write grant mapping */
     p2m_grant_map_ro,   /* Read-only grant mapping */
+    p2m_iommu_map_rw,   /* Read/write iommu mapping */
+    p2m_iommu_map_ro,   /* Read-only iommu mapping */
     p2m_max_real_type,  /* Types after this won't be store in the p2m */
 } p2m_type_t;
 
diff --git a/xen/include/asm-x86/grant_table.h b/xen/include/asm-x86/grant_table.h
index 3013869..e5ccf2b 100644
--- a/xen/include/asm-x86/grant_table.h
+++ b/xen/include/asm-x86/grant_table.h
@@ -65,6 +65,8 @@ static inline void gnttab_clear_flag(unsigned int nr, uint16_t *st)
 /* Done implicitly when page tables are destroyed. */
 #define gnttab_release_host_mappings(domain) ( paging_mode_external(domain) )
 
+#define gnttab_need_iommu_mapping(d)    !paging_mode_translate(d)
+
 static inline int replace_grant_supported(void)
 {
     return 1;
-- 
1.7.10.4