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

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Jan Beulich wrote on 2014-08-22:
>>>> On 20.08.14 at 18:01, <andrew.cooper3@xxxxxxxxxx> 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@xxxxxxxxxx>
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
> 
> 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).

Thanks for forwarding to us.

BTW, do you want us to give a ack or just let us know?

> 
> 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
> 
>


Best regards,
Yang


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel