Re: [Xen-devel] [PATCH 2/6] iommu: Introduce iommu_flush and iommu_flush_all.

[Jean Guyader <jean.guyader@xxxxxxxxxxxxx>]

On 08/11 08:24, Jan Beulich wrote:
> >>> On 07.11.11 at 18:06, Jean Guyader <jean.guyader@xxxxxxxxxxxxx> wrote:
> > On 07/11 04:42, Jan Beulich wrote:
> >> >>> On 07.11.11 at 16:16, Jean Guyader <jean.guyader@xxxxxxxxxxxxx> wrote:
> >> 
> >> > Signed-off-by: Jean Guyader <jean.guyader@xxxxxxxxxxxxx>
> >> > ---
> >> >  xen/drivers/passthrough/iommu.c     |   20 ++++++++++++++++++++
> >> >  xen/drivers/passthrough/vtd/iommu.c |   12 ++++++++++++
> >> >  xen/include/xen/iommu.h             |    5 +++++
> >> >  3 files changed, 37 insertions(+), 0 deletions(-)
> >> 
> >> In iommu_iotlb_flush() you check whether the to-be-called function
> >> pointer is NULL, whereas in iommu_iotlb_flush_all() you don't. I
> >> actually think the second behavior is the correct one, but that
> >> implies that you need to also implement respective AMD IOMMU
> >> functions.
> >> 
> > 
> > Yes, It's an error on my part. I've updated the patch to check
> > for the present of iotlb_flush_all before I call it now.
> 
> But as said, I don't think this is the right solution: How can it be
> correct on non-Intel hardware to have these functions simply do
> nothing?
> 

These functions are only here to counter balance the dont_flush_iotlb_flag.
If they don't acknowlage this flag doing nothing is the right thing to do.

That said I can probably implement a naive version for the AMD iommu
that will use amd_iommu_flush_pages once or in a loop.

Obviously I will remove the check for the non existing callback if I do
that as it become mandatory.

Jean

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