When shutting down the machine running a mainline Linux kernel, the
following error happens:

$ build/riscv64-softmmu/qemu-system-riscv64 -bios default -M virt \
    -display none -initrd rootfs.cpio -kernel Image -m 512m \
    -nodefaults -serial mon:stdio
...
Requesting system poweroff
[    4.999630] reboot: Power down
sbi_trap_error: hart0: trap handler failed (error -2)
sbi_trap_error: hart0: mcause=0x0000000000000007 mtval=0x0000000000100000
sbi_trap_error: hart0: mepc=0x000000008000d4cc mstatus=0x0000000000001822
sbi_trap_error: hart0: ra=0x000000008000999e sp=0x0000000080015c78
sbi_trap_error: hart0: gp=0xffffffe000e76610 tp=0xffffffe0081b89c0
sbi_trap_error: hart0: s0=0x0000000080015c88 s1=0x0000000000000040
sbi_trap_error: hart0: a0=0x0000000000000000 a1=0x0000000080004024
sbi_trap_error: hart0: a2=0x0000000080004024 a3=0x0000000080004024
sbi_trap_error: hart0: a4=0x0000000000100000 a5=0x0000000000005555
sbi_trap_error: hart0: a6=0x0000000000004024 a7=0x0000000080011158
sbi_trap_error: hart0: s2=0x0000000000000000 s3=0x0000000080016000
sbi_trap_error: hart0: s4=0x0000000000000000 s5=0x0000000000000000
sbi_trap_error: hart0: s6=0x0000000000000001 s7=0x0000000000000000
sbi_trap_error: hart0: s8=0x0000000000000000 s9=0x0000000000000000
sbi_trap_error: hart0: s10=0x0000000000000000 s11=0x0000000000000008
sbi_trap_error: hart0: t0=0x0000000000000000 t1=0x0000000000000000
sbi_trap_error: hart0: t2=0x0000000000000000 t3=0x0000000000000000
sbi_trap_error: hart0: t4=0x0000000000000000 t5=0x0000000000000000
sbi_trap_error: hart0: t6=0x0000000000000000

The kernel does a 16-bit write when powering off the machine, which
was allowed before commit 5d971f9e ("memory: Revert "memory: accept
mismatching sizes in memory_region_access_valid""). Make min_access_size
match reality so that the machine can shut down properly now.

Cc: qemu-stable@nongnu.org
Fixes: 88a07990 ("SiFive RISC-V Test Finisher")
Fixes: 5d971f9e ("memory: Revert "memory: accept mismatching sizes in memory_region_access_valid"")
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20200901055822.2721209-1-natechancellor@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>