vtd: add lookup_page method to iommu_ops

This patch adds a new method to the VT-d IOMMU implementation to find the
MFN currently mapped by the specified DFN along with a wrapper function
in generic IOMMU code to call the implementation if it exists.

NOTE: This patch only adds a Xen-internal interface. This will be used by
      a subsequent patch.
      Another subsequent patch will add similar functionality for AMD
      IOMMUs.
Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>

xen/drivers/passthrough/iommu.c

@@ -333,6 +333,17 @@ int iommu_unmap_page(struct domain *d, dfn_t dfn)
     return rc;
 }
 
+int iommu_lookup_page(struct domain *d, dfn_t dfn, mfn_t *mfn,
+                      unsigned int *flags)
+{
+    const struct domain_iommu *hd = dom_iommu(d);
+
+    if ( !iommu_enabled || !hd->platform_ops )
+        return -EOPNOTSUPP;
+
+    return hd->platform_ops->lookup_page(d, dfn, mfn, flags);
+}
+
 static void iommu_free_pagetables(unsigned long unused)
 {
     do {

xen/drivers/passthrough/vtd/iommu.c

@@ -1833,6 +1833,46 @@ static int __must_check intel_iommu_unmap_page(struct domain *d,
     return dma_pte_clear_one(d, dfn_to_daddr(dfn));
 }
 
+static int intel_iommu_lookup_page(struct domain *d, dfn_t dfn, mfn_t *mfn,
+                                   unsigned int *flags)
+{
+    struct domain_iommu *hd = dom_iommu(d);
+    struct dma_pte *page, val;
+    u64 pg_maddr;
+
+    /*
+     * If VT-d shares EPT page table or if the domain is the hardware
+     * domain and iommu_passthrough is set then pass back the dfn.
+     */
+    if ( iommu_use_hap_pt(d) ||
+         (iommu_hwdom_passthrough && is_hardware_domain(d)) )
+        return -EOPNOTSUPP;
+
+    spin_lock(&hd->arch.mapping_lock);
+
+    pg_maddr = addr_to_dma_page_maddr(d, dfn_to_daddr(dfn), 0);
+    if ( !pg_maddr )
+    {
+        spin_unlock(&hd->arch.mapping_lock);
+        return -ENOMEM;
+    }
+
+    page = map_vtd_domain_page(pg_maddr);
+    val = page[dfn_x(dfn) & LEVEL_MASK];
+
+    unmap_vtd_domain_page(page);
+    spin_unlock(&hd->arch.mapping_lock);
+
+    if ( !dma_pte_present(val) )
+        return -ENOENT;
+
+    *mfn = maddr_to_mfn(dma_pte_addr(val));
+    *flags = dma_pte_read(val) ? IOMMUF_readable : 0;
+    *flags |= dma_pte_write(val) ? IOMMUF_writable : 0;
+
+    return 0;
+}
+
 int iommu_pte_flush(struct domain *d, uint64_t dfn, uint64_t *pte,
                     int order, int present)
 {
@@ -2658,6 +2698,7 @@ const struct iommu_ops intel_iommu_ops = {
     .teardown = iommu_domain_teardown,
     .map_page = intel_iommu_map_page,
     .unmap_page = intel_iommu_unmap_page,
+    .lookup_page = intel_iommu_lookup_page,
     .free_page_table = iommu_free_page_table,
     .reassign_device = reassign_device_ownership,
     .get_device_group_id = intel_iommu_group_id,

xen/drivers/passthrough/vtd/iommu.h

@@ -272,6 +272,9 @@ struct dma_pte {
 #define dma_set_pte_prot(p, prot) do { \
         (p).val = ((p).val & ~DMA_PTE_PROT) | ((prot) & DMA_PTE_PROT); \
     } while (0)
+#define dma_pte_prot(p) ((p).val & DMA_PTE_PROT)
+#define dma_pte_read(p) (dma_pte_prot(p) & DMA_PTE_READ)
+#define dma_pte_write(p) (dma_pte_prot(p) & DMA_PTE_WRITE)
 #define dma_pte_addr(p) ((p).val & PADDR_MASK & PAGE_MASK_4K)
 #define dma_set_pte_addr(p, addr) do {\
             (p).val |= ((addr) & PAGE_MASK_4K); } while (0)

xen/include/xen/iommu.h

@@ -92,6 +92,8 @@ void iommu_teardown(struct domain *d);
 int __must_check iommu_map_page(struct domain *d, dfn_t dfn,
                                 mfn_t mfn, unsigned int flags);
 int __must_check iommu_unmap_page(struct domain *d, dfn_t dfn);
+int __must_check iommu_lookup_page(struct domain *d, dfn_t dfn, mfn_t *mfn,
+                                   unsigned int *flags);
 
 enum iommu_feature
 {
@@ -183,9 +185,17 @@ struct iommu_ops {
 #endif /* HAS_PCI */
 
     void (*teardown)(struct domain *d);
+
+    /*
+     * This block of operations must be appropriately locked against each
+     * other by the caller in order to have meaningful results.
+     */
     int __must_check (*map_page)(struct domain *d, dfn_t dfn, mfn_t mfn,
                                  unsigned int flags);
     int __must_check (*unmap_page)(struct domain *d, dfn_t dfn);
+    int __must_check (*lookup_page)(struct domain *d, dfn_t dfn, mfn_t *mfn,
+                                    unsigned int *flags);
+
     void (*free_page_table)(struct page_info *);
 #ifdef CONFIG_X86
     void (*update_ire_from_apic)(unsigned int apic, unsigned int reg, unsigned int value);