On 18.03.2025 16:35, Roger Pau Monné wrote:
> On Tue, Mar 18, 2025 at 03:33:03PM +0100, Jan Beulich wrote:
>> On 18.03.2025 10:19, Roger Pau Monne wrote:
>>> --- a/xen/arch/x86/include/asm/x86_64/uaccess.h
>>> +++ b/xen/arch/x86/include/asm/x86_64/uaccess.h
>>> @@ -9,9 +9,9 @@
>>> * a secondary mapping installed, which needs to be used for such accesses
>>> in
>>> * the PV case, and will also be used for HVM to avoid extra conditionals.
>>> */
>>> -#define COMPAT_ARG_XLAT_VIRT_BASE ((void *)ARG_XLAT_START(current) + \
>>> - (PERDOMAIN_ALT_VIRT_START - \
>>> - PERDOMAIN_VIRT_START))
>>> +#define COMPAT_ARG_XLAT_VIRT_BASE ((void *)ARG_XLAT_START(current) - \
>>> + (PERDOMAIN_VIRT_START - \
>>> + PERDOMAIN_ALT_VIRT_START))
>>
>> Aren't we then (still) dependent on ordering between PERDOMAIN_VIRT_START
>> and PERDOMAIN_ALT_VIRT_START? Would
>>
>> #define COMPAT_ARG_XLAT_VIRT_BASE ((void *)ARG_XLAT_START(current) - \
>> PERDOMAIN_VIRT_START + \
>> PERDOMAIN_ALT_VIRT_START)
>>
>> perhaps be less fragile?
>
> PERDOMAIN_{ALT_,}VIRT_START are unsigned long, so this might work.
>
> Note however that even with your suggestion we are still dependant on
> ARG_XLAT_START(v) > PERDOMAIN_ALT_VIRT_START, or else the '-' won't
> work. I think I prefer my proposed version, because it's clear that
> PERDOMAIN_VIRT_START, ARG_XLAT_START(current) >
> PERDOMAIN_ALT_VIRT_START.
What makes that clear? Can't we move PERDOMAIN_ALT_VIRT_START pretty
much at will?
Jan
> With your suggestion that's not obvious.
>
> Thanks, Roger.
