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

[Paolo Bonzini]

On 28/09/2018 14:28, Aldo Mazzeo wrote:
> 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.

Hi,

x86_64 is never active with paging disabled, so physical addresses with
paging disabled are always 32-bits.

In addition, physical addresses on x86 are constrained to 52-bits, so
that address is invalid.

Paolo

> 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.
>