vmap_to_mfn() uses virt_to_maddr(), which is designed to work with VA from
either the direct map region or Xen's linkage region (XEN_VIRT_START).
An assertion will occur if it is used with other regions, in particular for
the VMAP region.

Since RISC-V lacks a hardware feature to request the MMU to translate a VA to
a PA (as Arm does, for example), software page table walking (pt_walk()) is
used for the VMAP region to obtain the mfn from pte_t.

To avoid introduce a circular dependency between asm/mm.h and asm/page.h by
including each other, the static inline function  _vmap_to_mfn() is introduced
in asm/page.h, as it uses struct pte_t and pte_is_mapping() from asm/page.h.
_vmap_to_mfn() is then reused in the definition of vmap_to_mfn() macro in
asm/mm.h.

Fixes: 7db8d2bd9b ("xen/riscv: add minimal stuff to mm.h to build full Xen")
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
Changes in v5:
- Minor code style fixes.
- Add Reviewed-by: Jan Beulich <jbeulich@suse.com>.
---
Changes in v4:
- Convert _vmap_to_mfn() macro to static inline function.
- Update the commit message: change macro to static inline function for
  _vmap_to_mfn().
---
Changes in v3:
- Move vmap_to_mfn_ to asm/page.h to deal with circular dependency.
- Convert vmap_to_mfn_() to macros.
- Rename vmap_to_mfn_ to _vmap_to_mfn.
- Update _vmap_to_mfn() to work with pte_t instead of pte_t*.
- Add parentheses around va argument for macros vmap_to_mfn().
- Updated the commit message.
---
Changes in v2:
 - Update defintion of vmap_to_mfn() as pt_walk() now returns pte_t
   instead of paddr_t.
 - Update the commit message.
---
 xen/arch/riscv/include/asm/mm.h   | 2 +-
 xen/arch/riscv/include/asm/page.h | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/xen/arch/riscv/include/asm/mm.h b/xen/arch/riscv/include/asm/mm.h
index 292aa48fc1..4035cd400a 100644
--- a/xen/arch/riscv/include/asm/mm.h
+++ b/xen/arch/riscv/include/asm/mm.h
@@ -23,7 +23,7 @@ extern vaddr_t directmap_virt_start;
 #define gaddr_to_gfn(ga)    _gfn(paddr_to_pfn(ga))
 #define mfn_to_maddr(mfn)   pfn_to_paddr(mfn_x(mfn))
 #define maddr_to_mfn(ma)    _mfn(paddr_to_pfn(ma))
-#define vmap_to_mfn(va)     maddr_to_mfn(virt_to_maddr((vaddr_t)(va)))
+#define vmap_to_mfn(va)     _vmap_to_mfn((vaddr_t)(va))
 #define vmap_to_page(va)    mfn_to_page(vmap_to_mfn(va))
 
 static inline void *maddr_to_virt(paddr_t ma)
diff --git a/xen/arch/riscv/include/asm/page.h b/xen/arch/riscv/include/asm/page.h
index 0439a1a9ee..bf8988f657 100644
--- a/xen/arch/riscv/include/asm/page.h
+++ b/xen/arch/riscv/include/asm/page.h
@@ -210,6 +210,15 @@ static inline pte_t pte_from_mfn(mfn_t mfn, unsigned int flags)
 
 pte_t pt_walk(vaddr_t va, unsigned int *pte_level);
 
+static inline mfn_t _vmap_to_mfn(vaddr_t va)
+{
+    pte_t entry = pt_walk(va, NULL);
+
+    BUG_ON(!pte_is_mapping(entry));
+
+    return mfn_from_pte(entry);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* ASM__RISCV__PAGE_H */
-- 
2.48.1