Re: [PATCH kvm-unit-tests 01/17] x86: intel-iommu: add vt-d init test

[Peter Xu <peterx@redhat.com>]

On Tue, Nov 08, 2016 at 06:40:35PM +0100, Alexander Gordeev wrote:

[...]

> > Looks like Linux is using memory barrior and volatile keywords to do
> > the protection (build_mmio_read() for x86). I think at least I can add
> > volatile here for each read/write to make it safer. Do you think
> > that'll suffice here? E.g.:
> > 
> >   static inline uint64_t vtd_readq(unsigned int reg)
> >   {
> >       return *(volatile uint64_t *)(Q35_HOST_BRIDGE_IOMMU_ADDR + reg);
> >   }
> 
> Yeah, I think with volatile it is better. But I am still missing
> why not just use read/write which already exist and use volatile:
> 
> static inline u64 __raw_readq(const volatile void *addr)
> {
> 	assert(sizeof(unsigned long) == sizeof(u64));
> 	return *(const volatile u64 *)addr;
> }

That's nice! I'll use it. Thanks,

-- peterx