[Qemu-devel] Problem translating very high virtual addresses to physical on x86

[Aldo Mazzeo]

I was trying to translate a very high virtual address (like
0x0010000000000001) to physical on x86-64 with *paging disabled*. The
problem is that the obtained physical page is 0 because PG_ADDRESS_MASK
is applied to the pte in the virtual to physical to translation
(see target/i386/helper.c:842 in the 2.12.1 branch), cutting out the
high bits in the virtual address.

I tried to track back when this mask was introduced in the equation,
and I found the commit e7e898a76aa00e2238b119ed2910442b1c3cacdd which
replaces PHYS_ADDR_MASK with PG_ADDRESS_MASK and moves the line in a
section of code that is executed even if paging is disabled. In my
opinion, PG_ADDRESS_MASK should not be applied when paging is disabled,
but I would like to have some expert's opinion on this.