Re: [PATCH] x86/ats: Disable Address Translation Services by default

[Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>]

Andrew/Jan,

I have verified that PCI device pass-through works with ATS disabled. 
Although, could you please help described how "asynchronous queued 
invalidation support" supposed to work?

Thanks,

Suravee

On 08/22/2014 07:39 AM, Jan Beulich wrote:
>>>> On 20.08.14 at 18:01, <andrew.cooper3@citrix.com> wrote:
>> Xen cannot safely use any ATS functionality until it gains asynchronous
>> queued
>> invalidation support, because of the current synchronous wait for
>> completion.
>>
>> Do not turn ATS on by default.
>>
>> While editing the default in the command line documentation, correct the
>> statement regarding PCI Passthrough.  ATS is purely a performance
>> optimisation, and is certainly not required for PCI Passthrough to function.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
>> CC: Jan Beulich <JBeulich@suse.com>
>
> Even if not mandated by ./MAINTAINERS I think this definitely
> should have been Cc-ed to the VT-d and AMD IOMMU maintainers
> (now done).
>
> Jan
>
>> ---
>>   docs/misc/xen-command-line.markdown |    9 ++++++---
>>   xen/drivers/passthrough/x86/ats.c   |    2 +-
>>   2 files changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/docs/misc/xen-command-line.markdown
>> b/docs/misc/xen-command-line.markdown
>> index a8cab59..5f4680f 100644
>> --- a/docs/misc/xen-command-line.markdown
>> +++ b/docs/misc/xen-command-line.markdown
>> @@ -176,10 +176,13 @@ developers wishing Xen to fall back to older timing
>> methods on newer hardware.
>>   ### ats
>>   > `= <boolean>`
>>
>> -> Default: `true`
>> +> Default: `false`
>> +
>> +Permits Xen to set up and use PCI Address Translation Services.  This is a
>> +performance optimisation for PCI Passthrough.
>>
>> -Permits Xen to set up and use PCI Address Translation Services, which
>> -is required for PCI Passthrough.
>> +**WARNING: Xen cannot currently safely use ATS because of its synchronous
>> wait
>> +loops for Queued Invalidation completions.**
>>
>>   ### availmem
>>   > `= <size>`
>> diff --git a/xen/drivers/passthrough/x86/ats.c
>> b/xen/drivers/passthrough/x86/ats.c
>> index 1e3e03a..436eada 100644
>> --- a/xen/drivers/passthrough/x86/ats.c
>> +++ b/xen/drivers/passthrough/x86/ats.c
>> @@ -20,7 +20,7 @@
>>
>>   LIST_HEAD(ats_devices);
>>
>> -bool_t __read_mostly ats_enabled = 1;
>> +bool_t __read_mostly ats_enabled = 0;
>>   boolean_param("ats", ats_enabled);
>>
>>   int enable_ats_device(int seg, int bus, int devfn, const void *iommu)
>> --
>> 1.7.10.4
>
>
>