On 28/09/2020 15:49, Jan Beulich wrote:
> On 28.09.2020 14:47, Andrew Cooper wrote:
>> On 28/09/2020 13:05, Jan Beulich wrote:
>>> --- a/xen/include/asm-x86/regs.h
>>> +++ b/xen/include/asm-x86/regs.h
>>> @@ -15,4 +15,18 @@
>>> (diff == 0);
>>> \
>>> })
>>>
>>> +#define read_sreg(name) ({ \
>>> + unsigned int __sel; \
>>> + asm volatile ( "mov %%" STR(name) ",%0" : "=r" (__sel) ); \
>>> + __sel; \
>>> +})
>>> +
>>> +static inline void read_sregs(struct cpu_user_regs *regs)
>>> +{
>>> + asm volatile ( "mov %%ds, %0" : "=m" (regs->ds) );
>>> + asm volatile ( "mov %%es, %0" : "=m" (regs->es) );
>>> + asm volatile ( "mov %%fs, %0" : "=m" (regs->fs) );
>>> + asm volatile ( "mov %%gs, %0" : "=m" (regs->gs) );
>> It occurs to me that reads don't need to be volatile. There are no side
>> effects.
> I'll do the same for what patches 3 and 5 alter anyway, assuming
> this won't invalidate your R-b there.
3 is fine. 5 is a little more problematic, because there are
serialising side effects, but I suppose we really don't care here.
~Andrew
