Re: [Xen-devel] [PATCH] VT-d: suppress individual flushes during hwdom setup

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.05.19 at 15:08, <roger.pau@xxxxxxxxxx> wrote:
> On Thu, May 02, 2019 at 06:28:06AM -0600, Jan Beulich wrote:
>> There's an invocation of iommu_flush_all() immediately afterwards.
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> --- a/xen/drivers/passthrough/vtd/iommu.c
>> +++ b/xen/drivers/passthrough/vtd/iommu.c
>> @@ -1310,8 +1310,11 @@ static void __hwdom_init intel_iommu_hwd
>>  
>>      setup_hwdom_pci_devices(d, setup_hwdom_device);
>>      setup_hwdom_rmrr(d);
>> +
>>      /* Make sure workarounds are applied before enabling the IOMMU(s). */
>> +    this_cpu(iommu_dont_flush_iotlb) = true;
>>      arch_iommu_hwdom_init(d);
>> +    this_cpu(iommu_dont_flush_iotlb) = false;
> 
> Don't you want to also avoid flushes in setup_hwdom_rmrr and
> setup_hwdom_pci_devices?

We probably could, but the gain would be much lower because
there are far fewer pages involved there.

Jan



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