target/riscv: Fix Guest Physical Address Translation

target/riscv: Fix Guest Physical Address Translation

Before changing the flow check for sv39/48/57.

According to specification (for Supervisor mode):
Sv39 implementations support a 39-bit virtual address space, divided into 4 KiB
pages.
Instruction fetch addresses and load and store effective addresses, which are
64 bits,
must have bits 63–39 all equal to bit 38, or else a page-fault exception will
occur.
Likewise for Sv48 and Sv57.

So the high bits are equal to bit 38 for sv39.

According to specification (for Hypervisor mode):
For Sv39x4, address bits of the guest physical address 63:41 must all be zeros,
or else a
guest-page-fault exception occurs.

Likewise for Sv48x4 and Sv57x4.
For Sv48x4 address bits 63:50 must all be zeros, or else a guest-page-fault
exception occurs.
For Sv57x4 address bits 63:59 must all be zeros, or else a guest-page-fault
exception occurs.

For example we are trying to access address 0xffff_ffff_ff01_0000 with only
G-translation enabled.
So expected behavior is to generate exception. But qemu doesn't generate such
exception.

For the old check, we get
va_bits == 41, mask == (1 << 24) - 1, masked_msbs == (0xffff_ffff_ff01_0000 >>
40) & mask == mask.
Accordingly, the condition masked_msbs != 0 && masked_msbs != mask is not
fulfilled
and the check passes.

Signed-off-by: Irina Ryapolova <irina.ryapolova@syntacore.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230418075423.26217-1-irina.ryapolova@syntacore.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>