Re: [Qemu-devel] [PATCH qemu] vfio/spapr: Allow fallback to SPAPR TCE IOMMU v1

[Alexey Kardashevskiy]

On 23/11/17 00:39, David Gibson wrote:
> On Wed, Nov 22, 2017 at 04:15:52PM +1100, Alexey Kardashevskiy wrote:
>> The vfio_iommu_spapr_tce driver always advertises v1 and v2 IOMMU support,
>> however PR KVM (a special version of KVM designed to work in
>> a paravirtualized system; these days used for nested virtualizaion) only
>> supports the "pseries" platform which does not support v2. Since there is
>> no way to choose the IOMMU version in QEMU, it fails to start.
>>
>> This adds a fallback to the v1 IOMMU if v2 cannot be used.
>>
>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
> 
> The fallback itself isn't a bad idea, but your commit message contains
> several inaccurracies.  KVM PR is not particularly designed to work in
> a paravirtualized system, and it doesn't only support the pseries
> platform (as guest *or* host).  It's actually a lot more general than
> KVM HV - just slow, not that well tested and missing a number of
> features that no-one's bothered to port to it.

Well, true. I kinda tried to give an example of how this may be useful and
exaggerated a bit, plus my ignorance :) I'll repost if Alex does not have
objections otherwise.



> 
>> ---
>>  hw/vfio/common.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 7b2924c..cd81cc9 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -1040,6 +1040,11 @@ static int vfio_connect_container(VFIOGroup *group, 
>> AddressSpace *as,
>>              v2 ? VFIO_SPAPR_TCE_v2_IOMMU : VFIO_SPAPR_TCE_IOMMU;
>>          ret = ioctl(fd, VFIO_SET_IOMMU, container->iommu_type);
>>          if (ret) {
>> +            container->iommu_type = VFIO_SPAPR_TCE_IOMMU;
>> +            v2 = false;
>> +            ret = ioctl(fd, VFIO_SET_IOMMU, container->iommu_type);
>> +        }
>> +        if (ret) {
>>              error_setg_errno(errp, errno, "failed to set iommu for 
>> container");
>>              ret = -errno;
>>              goto free_container_exit;
> 


-- 
Alexey

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