Introduce helpers pte_{set,get}_mfn() to simplify setting and getting
of mfn.

Also, introduce PTE_PPN_MASK and add BUILD_BUG_ON() to be sure that
PTE_PPN_MASK remains the same for all MMU modes except Sv32.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
Changes in V4-V5:
 - Nothing changed. Only Rebase.
---
Changes in V3:
 - Add Acked-by: Jan Beulich <jbeulich@suse.com>.
---
Changes in V2:
 - Patch "[PATCH v1 4/6] xen/riscv: define pt_t and pt_walk_t structures" was
   renamed to xen/riscv: introduce pte_{set,get}_mfn() as after dropping of
   bitfields for PTE structure, this patch introduce only pte_{set,get}_mfn().
 - As pt_t and pt_walk_t were dropped, update implementation of
   pte_{set,get}_mfn() to use bit operations and shifts instead of bitfields.
 - Introduce PTE_PPN_MASK to be able to use MASK_INSR for setting/getting PPN.
 - Add BUILD_BUG_ON(RV_STAGE1_MODE > SATP_MODE_SV57) to be sure that when
   new MMU mode will be added, someone checks that PPN is still bits 53:10.
---
 xen/arch/riscv/include/asm/page.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/xen/arch/riscv/include/asm/page.h b/xen/arch/riscv/include/asm/page.h
index ddcc4da0a3..66cb192316 100644
--- a/xen/arch/riscv/include/asm/page.h
+++ b/xen/arch/riscv/include/asm/page.h
@@ -112,6 +112,30 @@ typedef struct {
 #endif
 } pte_t;
 
+#if RV_STAGE1_MODE != SATP_MODE_SV32
+#define PTE_PPN_MASK _UL(0x3FFFFFFFFFFC00)
+#else
+#define PTE_PPN_MASK _U(0xFFFFFC00)
+#endif
+
+static inline void pte_set_mfn(pte_t *p, mfn_t mfn)
+{
+    /*
+     * At the moment spec provides Sv32 - Sv57.
+     * If one day new MMU mode will be added it will be needed
+     * to check that PPN mask still continue to cover bits 53:10.
+     */
+    BUILD_BUG_ON(RV_STAGE1_MODE > SATP_MODE_SV57);
+
+    p->pte &= ~PTE_PPN_MASK;
+    p->pte |= MASK_INSR(mfn_x(mfn), PTE_PPN_MASK);
+}
+
+static inline mfn_t pte_get_mfn(pte_t p)
+{
+    return _mfn(MASK_EXTR(p.pte, PTE_PPN_MASK));
+}
+
 static inline bool pte_is_valid(pte_t p)
 {
     return p.pte & PTE_VALID;
-- 
2.51.0