Re: [PATCH 5/9] i386: Add address spaces for fs/gs segments

[Paolo Bonzini <bonzini@gnu.org>]

On 08/10/2015 06:59, Richard Henderson wrote:
> +/* Address space support.
> +
> +   This is not "far pointers" in the 16-bit sense, but an easy way
> +   to use %fs and %gs segment prefixes.  Therefore:
> +
> +    (a) All address spaces have the same modes,
> +    (b) All address spaces have the same addresss forms,
> +    (c) While %fs and %gs are technically subsets of the generic
> +        address space, they are probably not subsets of each other.
> +    (d) Since we have no access to the segment base register values
> +        without resorting to a system call, we cannot convert a
> +        non-default address space to a default address space.
> +        Therefore we do not claim %fs or %gs are subsets of generic.

rdfsbase and rdgsbase are potentially accessible to userspace too, so I
think %fs or %gs should be considered subsets of generic.

Paolo

> +   Therefore, we need not override any of the address space hooks.  */