Re: [Xen-devel] [PATCH] vt-d: use two 32-bit writes to update DMAR fault address registers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.09.17 at 08:00, <haozhong.zhang@xxxxxxxxx> wrote:
> The 64-bit DMAR fault address is composed of two 32 bits registers
> DMAR_FEADDR_REG and DMAR_FEUADDR_REG. According to VT-d spec:
> "Software is expected to access 32-bit registers as aligned doublewords",
> a hypervisor should use two 32-bit writes to DMAR_FEADDR_REG and
> DMAR_FEUADDR_REG separately in order to update a 64-bit fault address,
> rather than a 64-bit write to DMAR_FEADDR_REG.
> 
> Though I haven't seen any errors caused by such one 64-bit write on
> real machines, it's still better to follow the specification.

Any sane chipset should split qword accesses into dword ones if
they can't be handled at some layer. Also if you undo something
explicitly done by an earlier commit, please quote that commit
and say what was wrong. After all Kevin as the VT-d maintainer
agreed with the change back then.

Jan


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