[PATCH v1 3/3] xen/riscv: update mfn calculation in pt_mapping_level()

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

When pt_update() is called with arguments (..., INVALID_MFN, ..., 0 or 1),
it indicates that a mapping is being destroyed/modifyed.

`mfn` should be set properly in cases when modifying/destroying a  mapping
to ensure the correct page table `level` is returned. In the  case of
`mfn` == INVALID_MFN, the `mask` will take into account only `vfn` and could
accidentally return an incorrect level.
For example,  if `vfn` is page table level 1 aligned, but it was mapped as
page table level 0, then without the check below it will return `level` = 1
because only `vfn`, which is page table level 1 aligned, is taken into
account when `mfn` == INVALID_MFN.

To address this issue, during the destruction/modification of a mapping,
physical address is calculated for provided `va`. This ensures that the
appropriate mask is generated, resulting in the correct calculation of
the level.

Fixes: c2f1ded524 ("xen/riscv: page table handling")
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/arch/riscv/pt.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/xen/arch/riscv/pt.c b/xen/arch/riscv/pt.c
index 865d60d1af..c8bc6f7e37 100644
--- a/xen/arch/riscv/pt.c
+++ b/xen/arch/riscv/pt.c
@@ -346,9 +346,33 @@ static int pt_mapping_level(unsigned long vfn, mfn_t mfn, 
unsigned long nr,
         return level;
 
     /*
-     * Don't take into account the MFN when removing mapping (i.e
-     * MFN_INVALID) to calculate the correct target order.
+     * `mfn` should be set properly in cases when modifying/destroying a
+     * mapping to ensure the correct page table `level` is received. In the
+     * case of `mfn` == INVALID_MFN, the `mask` will take into account only
+     * `vfn` and could accidentally return an incorrect level. For example,
+     * if `vfn` is page table level 1 aligned, but it was mapped as page table
+     * level 0, then without the check below it will return `level` = 1
+     * because only `vfn`, which is page table level 1 aligned, is taken into
+     * account when `mfn` == INVALID_MFN.
      *
+     * POPULATE shouldn't be considered as `va` hasn't been mapped yet.
+     */
+    if ( mfn_eq(mfn, INVALID_MFN) && !(flags & PTE_POPULATE) )
+    {
+        vaddr_t va = vfn << PAGE_SHIFT;
+        paddr_t pa;
+        unsigned long xen_virt_end = (XEN_VIRT_START + XEN_VIRT_SIZE - 1);
+
+        if ( ((va >= DIRECTMAP_VIRT_START) && (va <= DIRECTMAP_VIRT_END)) ||
+             ((va >= XEN_VIRT_START) && (va <= xen_virt_end)) )
+            pa = virt_to_maddr(va);
+        else
+            pa = pt_walk(va);
+
+        mfn = _mfn(paddr_to_pfn(pa));
+    }
+
+    /*
      * `vfn` and `mfn` must be both superpage aligned.
      * They are or-ed together and then checked against the size of
      * each level.
-- 
2.48.1