target/riscv: Fix incorrect PTE merge in walk_pte

target/riscv: Fix incorrect PTE merge in walk_pte

Two non-subsequent PTEs can be mapped to subsequent paddrs. In this
case, walk_pte will erroneously merge them.

Enforce the split up, by tracking the virtual base address.

Let's say we have the mapping:
0x81200000 -> 0x89623000 (4K)
0x8120f000 -> 0x89624000 (4K)

Before, walk_pte would have shown:

vaddr            paddr            size             attr
---------------- ---------------- ---------------- -------
0000000081200000 0000000089623000 0000000000002000 rwxu-ad

as it only checks for subsequent paddrs. With this patch, it becomes:

vaddr            paddr            size             attr
---------------- ---------------- ---------------- -------
0000000081200000 0000000089623000 0000000000001000 rwxu-ad
000000008120f000 0000000089624000 0000000000001000 rwxu-ad

Signed-off-by: Ralf Ramsauer <ralf.ramsauer@oth-regensburg.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20220423215907.673663-1-ralf.ramsauer@oth-regensburg.de>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>