[PATCH v3 14/20] xen/riscv: Implement p2m_pte_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_pte_from_mfn(): Generates a valid PTE using the
  given MFN, p2m_type_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_set_type(): Stores the p2m type in PTE's bits. The storage of types,
  which don't fit PTE bits, will be implemented separately later.

PBMT type encoding support:
- Introduces an enum pbmt_type_t to represent the PBMT field values.
- Maps types like p2m_mmio_direct_dev to p2m_mmio_direct_io, others default
  to pbmt_pma.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in V3:
 - s/p2m_entry_from_mfn/p2m_pte_from_mfn.
 - s/pbmt_type_t/pbmt_type.
 - s/pbmt_max/pbmt_count.
 - s/p2m_type_radix_set/p2m_set_type.
 - Rework p2m_set_type() to handle only types which are fited into PTEs bits.
   Other types will be covered separately.
   Update arguments of p2m_set_type(): there is no any reason for p2m anymore.
 - p2m_set_permissions() updates:
   - Update the code in p2m_set_permission() for cases p2m_raw_rw and
     p2m_mmio_direct_io to set proper type permissions.
   - Add cases for p2m_grant_map_rw and p2m_grant_map_ro.
   - Use ASSERT_UNEACHABLE() instead of BUG() in switch cases of
     p2m_set_permissions.
   - Add blank lines non-fall-through case blocks in switch cases.
 - Set MFN before permissions are set in p2m_pte_from_mfn().
 - Update prototype of p2m_entry_from_mfn().
---
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              | 81 +++++++++++++++++++++++++++++--
 2 files changed, 85 insertions(+), 4 deletions(-)

diff --git a/xen/arch/riscv/include/asm/page.h 
b/xen/arch/riscv/include/asm/page.h
index cb303af0c0..4fa0556073 100644
--- a/xen/arch/riscv/include/asm/page.h
+++ b/xen/arch/riscv/include/asm/page.h
@@ -74,6 +74,14 @@
 #define PTE_SMALL       BIT(10, UL)
 #define PTE_POPULATE    BIT(11, UL)
 
+enum pbmt_type {
+    pbmt_pma,
+    pbmt_nc,
+    pbmt_io,
+    pbmt_rsvd,
+    pbmt_count,
+};
+
 #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 2467e459cc..efc7320619 100644
--- a/xen/arch/riscv/p2m.c
+++ b/xen/arch/riscv/p2m.c
@@ -1,3 +1,4 @@
+#include <xen/bug.h>
 #include <xen/domain_page.h>
 #include <xen/mm.h>
 #include <xen/rwlock.h>
@@ -197,6 +198,18 @@ 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_set_type(pte_t *pte, p2m_type_t t)
+{
+    int rc = 0;
+
+    if ( t > p2m_ext_storage )
+        panic("unimplemeted\n");
+    else
+        pte->pte |= MASK_INSR(t, P2M_TYPE_PTE_BITS_MASK);
+
+    return rc;
+}
+
 static p2m_type_t p2m_get_type(const pte_t pte)
 {
     p2m_type_t type = MASK_EXTR(pte.pte, P2M_TYPE_PTE_BITS_MASK);
@@ -222,11 +235,71 @@ static inline void p2m_clean_pte(pte_t *p, bool clean_pte)
     p2m_write_pte(p, pte, clean_pte);
 }
 
-static pte_t p2m_pte_from_mfn(mfn_t mfn, p2m_type_t t)
+static void p2m_set_permission(pte_t *e, p2m_type_t t)
 {
-    panic("%s: hasn't been implemented yet\n", __func__);
+    e->pte &= ~PTE_ACCESS_MASK;
+
+    switch ( t )
+    {
+    case p2m_grant_map_rw:
+    case p2m_ram_rw:
+        e->pte |= PTE_READABLE | PTE_WRITABLE;
+        break;
+
+    case p2m_ext_storage:
+    case p2m_mmio_direct_io:
+        e->pte |= PTE_ACCESS_MASK;
+        break;
+
+    case p2m_invalid:
+        e->pte &= ~(PTE_ACCESS_MASK | PTE_VALID);
+        break;
+
+    case p2m_grant_map_ro:
+        e->pte |= PTE_READABLE;
+        break;
+
+    default:
+        ASSERT_UNREACHABLE();
+        break;
+    }
+}
+
+static pte_t p2m_pte_from_mfn(mfn_t mfn, p2m_type_t t, bool is_table)
+{
+    pte_t e = (pte_t) { PTE_VALID };
+
+    switch ( t )
+    {
+    case p2m_mmio_direct_io:
+        e.pte |= PTE_PBMT_IO;
+        break;
+
+    default:
+        break;
+    }
+
+    pte_set_mfn(&e, mfn);
+
+    ASSERT(!(mfn_to_maddr(mfn) & ~PADDR_MASK));
+
+    if ( !is_table )
+    {
+        p2m_set_permission(&e, t);
+
+        if ( t < p2m_ext_storage )
+            p2m_set_type(&e, t);
+        else
+            panic("unimplemeted\n");
+    }
+    else
+        /*
+         * According to the spec and table "Encoding of PTE R/W/X fields":
+         *   X=W=R=0 -> Pointer to next level of page table.
+         */
+        e.pte &= ~PTE_ACCESS_MASK;
 
-    return (pte_t) { .pte = 0 };
+    return e;
 }
 
 #define P2M_TABLE_MAP_NONE 0
@@ -469,7 +542,7 @@ static int p2m_set_entry(struct p2m_domain *p2m,
         p2m_clean_pte(entry, p2m->clean_pte);
     else
     {
-        pte_t pte = p2m_pte_from_mfn(mfn, t);
+        pte_t pte = p2m_pte_from_mfn(mfn, t, false);
 
         p2m_write_pte(entry, pte, p2m->clean_pte);
 
-- 
2.50.1