Re: [Xen-devel] [PATCH 2/2] IOMMU/MMU: Adjust low level functions for VT-d Device-TLB flush error.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.04.16 at 05:27, <quan.xu@xxxxxxxxx> wrote:
> On April 11, 2016 11:10am, <quan.xu@xxxxxxxxx> wrote:
>> On March 29, 2016 3:37pm, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> > >>> On 25.03.16 at 10:27, <quan.xu@xxxxxxxxx> wrote:
>> > > On March 18, 2016 6:20pm, <JBeulich@xxxxxxxx> wrote:
>> > >> >>> On 17.03.16 at 07:54, <quan.xu@xxxxxxxxx> wrote:
>> > >> > --- a/xen/drivers/passthrough/iommu.c
>> > >> > +++ b/xen/drivers/passthrough/iommu.c
>> > >> > @@ -554,11 +555,24 @@ static void iommu_flush_all(void)
>> > >> >          iommu = drhd->iommu;
>> > >> >          iommu_flush_context_global(iommu, 0);
>> > >> >          flush_dev_iotlb = find_ats_dev_drhd(iommu) ? 1 : 0;
>> > >> > -        iommu_flush_iotlb_global(iommu, 0, flush_dev_iotlb);
>> > >> > +        rc = iommu_flush_iotlb_global(iommu, 0,
>> > >> > + flush_dev_iotlb);
>> > >> > +
>> > >> > +        if ( rc > 0 )
>> > >> > +        {
>> > >> > +            iommu_flush_write_buffer(iommu);
>> > >>
>> > >> Why is this needed all of the sudden?
>> > >
>> > > As there may be multiple IOMMUs. .e.g, there are 2 IOMMUs in my
>> > > machine, and I can find the following log message:
>> > > """
>> > > (XEN) Intel VT-d iommu 0 supported page sizes: 4kB, 2MB, 1GB.
>> > > (XEN) Intel VT-d iommu 1 supported page sizes: 4kB, 2MB, 1GB.
>> > > """
>> > > __iiuc__, iommu_flush_write_buffer() is per IOMMU, so It should be
>> > > called to flush every IOMMU.
>> >
>> > For one what you say suggests that right now this is being done for
>> > some (one?) IOMMU(s), which I don't see being the case. And then what
>> > you say _still_ doesn't say _why_ this is now needed all of the
>> > sudden. If, in the course of doing your re-work here, you find
>> > pre-existing issues with the code, please split the necessary fixes
>> > out of your re-work and submit them separately with proper explanations in
>> their commit messages.
>> >
>> 
>> I find out it is no need modification for this function.
> Sorry, this modification refers to as:
> "
> +        if ( rc > 0 )
> +        {
> +            iommu_flush_write_buffer(iommu);
> +            rc = 0;
> +        }
> "
> 
> at least errors need to be propagated.

How does error propagation correlate with suddenly calling
iommu_flush_write_buffer()?

Jan


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