[PATCH v2 13/17] xen/riscv: Implement p2m_entry_from_mfn() and support PBMT configuration

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

This patch adds the initial logic for constructing PTEs from MFNs in the RISC-V
p2m subsystem. It includes:
- Implementation of p2m_entry_from_mfn(): Generates a valid PTE using the
  given MFN, p2m_type_t, and p2m_access_t, including permission encoding and
  PBMT attribute setup.
- New helper p2m_set_permission(): Encodes access rights (r, w, x) into the
  PTE based on both p2m type and access permissions.
- p2m_type_radix_set(): Stores the p2m type in a radix tree keyed by the PTE
  for later retrieval.

PBMT type encoding support:
- Introduces an enum pbmt_type_t to represent the PBMT field values.
- Maps types like p2m_mmio_direct_dev to pbmt_io, others default to pbmt_pma.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in V2:
 - New patch. It was a part of a big patch "xen/riscv: implement p2m mapping
   functionality" which was splitted to smaller.
---
 xen/arch/riscv/include/asm/page.h |   8 +++
 xen/arch/riscv/p2m.c              | 103 ++++++++++++++++++++++++++++--
 2 files changed, 107 insertions(+), 4 deletions(-)

diff --git a/xen/arch/riscv/include/asm/page.h 
b/xen/arch/riscv/include/asm/page.h
index c67b9578c9..1d1054fa5c 100644
--- a/xen/arch/riscv/include/asm/page.h
+++ b/xen/arch/riscv/include/asm/page.h
@@ -76,6 +76,14 @@
 #define PTE_SMALL       BIT(10, UL)
 #define PTE_POPULATE    BIT(11, UL)
 
+enum pbmt_type_t {
+    pbmt_pma,
+    pbmt_nc,
+    pbmt_io,
+    pbmt_rsvd,
+    pbmt_max,
+};
+
 #define PTE_ACCESS_MASK (PTE_READABLE | PTE_WRITABLE | PTE_EXECUTABLE)
 
 #define PTE_PBMT_MASK   (PTE_PBMT_NOCACHE | PTE_PBMT_IO)
diff --git a/xen/arch/riscv/p2m.c b/xen/arch/riscv/p2m.c
index 6b11e87b22..cba04acf38 100644
--- a/xen/arch/riscv/p2m.c
+++ b/xen/arch/riscv/p2m.c
@@ -345,6 +345,26 @@ static pte_t *p2m_get_root_pointer(struct p2m_domain *p2m, 
gfn_t gfn)
     return __map_domain_page(p2m->root + root_table_indx);
 }
 
+static int p2m_type_radix_set(struct p2m_domain *p2m, pte_t pte, p2m_type_t t)
+{
+    int rc;
+    gfn_t gfn = mfn_to_gfn(p2m->domain, mfn_from_pte(pte));
+
+    rc = radix_tree_insert(&p2m->p2m_type, gfn_x(gfn),
+                           radix_tree_int_to_ptr(t));
+    if ( rc == -EEXIST )
+    {
+        /* If a setting already exists, change it to the new one */
+        radix_tree_replace_slot(
+            radix_tree_lookup_slot(
+                &p2m->p2m_type, gfn_x(gfn)),
+            radix_tree_int_to_ptr(t));
+        rc = 0;
+    }
+
+    return rc;
+}
+
 static p2m_type_t p2m_type_radix_get(struct p2m_domain *p2m, pte_t pte)
 {
     void *ptr;
@@ -389,12 +409,87 @@ static inline void p2m_remove_pte(pte_t *p, bool 
clean_pte)
     p2m_write_pte(p, pte, clean_pte);
 }
 
-static pte_t p2m_entry_from_mfn(struct p2m_domain *p2m, mfn_t mfn,
-                                p2m_type_t t, p2m_access_t a)
+static void p2m_set_permission(pte_t *e, p2m_type_t t, p2m_access_t a)
 {
-    panic("%s: hasn't been implemented yet\n", __func__);
+    /* First apply type permissions */
+    switch ( t )
+    {
+    case p2m_ram_rw:
+        e->pte |= PTE_ACCESS_MASK;
+        break;
+
+    case p2m_mmio_direct_dev:
+        e->pte |= (PTE_READABLE | PTE_WRITABLE);
+        e->pte &= ~PTE_EXECUTABLE;
+        break;
+
+    case p2m_invalid:
+        e->pte &= ~PTE_ACCESS_MASK;
+        break;
+
+    default:
+        BUG();
+        break;
+    }
+
+    /* Then restrict with access permissions */
+    switch ( a )
+    {
+    case p2m_access_rwx:
+        break;
+    case p2m_access_wx:
+        e->pte &= ~PTE_READABLE;
+        break;
+    case p2m_access_rw:
+        e->pte &= ~PTE_EXECUTABLE;
+        break;
+    case p2m_access_w:
+        e->pte &= ~(PTE_READABLE | PTE_EXECUTABLE);
+        e->pte &= ~PTE_EXECUTABLE;
+        break;
+    case p2m_access_rx:
+    case p2m_access_rx2rw:
+        e->pte &= ~PTE_WRITABLE;
+        break;
+    case p2m_access_x:
+        e->pte &= ~(PTE_READABLE | PTE_WRITABLE);
+        break;
+    case p2m_access_r:
+        e->pte &= ~(PTE_WRITABLE | PTE_EXECUTABLE);
+        break;
+    case p2m_access_n:
+    case p2m_access_n2rwx:
+        e->pte &= ~PTE_ACCESS_MASK;
+        break;
+    default:
+        BUG();
+        break;
+    }
+}
+
+static pte_t p2m_entry_from_mfn(struct p2m_domain *p2m, mfn_t mfn, p2m_type_t 
t, p2m_access_t a)
+{
+    pte_t e = (pte_t) { 1 };
+
+    switch ( t )
+    {
+    case p2m_mmio_direct_dev:
+        e.pte |= PTE_PBMT_IO;
+        break;
+
+    default:
+        break;
+    }
+
+    p2m_set_permission(&e, t, a);
+
+    ASSERT(!(mfn_to_maddr(mfn) & ~PADDR_MASK));
+
+    pte_set_mfn(&e, mfn);
+
+    BUG_ON(p2m_type_radix_set(p2m, e, t));
 
-    return (pte_t) { .pte = 0 };
+    return e;
 }
 
 #define GUEST_TABLE_MAP_NONE 0
-- 
2.49.0