Re: [Xen-devel] [PATCH] x86/HVM: refuse doing string operations in certain situations

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.09.13 at 22:05, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> On Fri, Sep 20, 2013 at 02:08:45PM +0100, Jan Beulich wrote:
>> We shouldn't do any acceleration for
>> - "rep movs" when either side is passed through MMIO or when both sides
>>   are handled by qemu
>> - "rep ins" and "rep outs" when the memory operand is any kind of MMIO
> 
> Could you explain this in a bit more details?
> 
> Why is acceleration in those cases bad?

- we currently can't have more than one request issued to qemu
  for a single guest side instruction (there's only one ioreq_t
  instance per vCPU)
- hvm_copy_{to,from}_guest_phys() don't honor the original
  access size

Jan


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