Re: [Xen-devel] [v4 04/17] iommu: Add iommu_intpost to control VT-d Posted-Interrupts feature

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/07/15 15:01, Andrew Cooper wrote:
> On 23/07/15 12:35, Feng Wu wrote:
>> VT-d Posted-Interrupts is an enhancement to CPU side Posted-Interrupt.
>> With VT-d Posted-Interrupts enabled, external interrupts from
>> direct-assigned devices can be delivered to guests without VMM
>> intervention when guest is running in non-root mode.
>>
>> This patch adds variable 'iommu_intpost' to control whether enable VT-d
>> posted-interrupt or not in the generic IOMMU code.
>>
>> CC: Jan Beulich <jbeulich@xxxxxxxx>
>> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
>> Signed-off-by: Feng Wu <feng.wu@xxxxxxxxx>
>> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Please patch docs/misc/xen-command-line.markdown as you are
>
>> ---
>> v4:
>> - No changes
>>
>> v3:
>> - Remove pointless initializer for 'iommu_intpost'.
>> - Some adjustment for "if no intremap then no intpost" logic.
>>     * For parse_iommu_param(), move it to the end of the function,
>>       so we don't need to add the some logic when introduing the
>>       new kernel parameter 'intpost' in later patch.
>>     * Add this logic in iommu_setup() after iommu_hardware_setup()
>>       is called.
>>
>>  xen/drivers/passthrough/iommu.c | 17 ++++++++++++++++-
>>  xen/include/xen/iommu.h         |  2 +-
>>  2 files changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/xen/drivers/passthrough/iommu.c 
>> b/xen/drivers/passthrough/iommu.c
>> index 06cb38f..536b69f 100644
>> --- a/xen/drivers/passthrough/iommu.c
>> +++ b/xen/drivers/passthrough/iommu.c
>> @@ -39,6 +39,7 @@ static void iommu_dump_p2m_table(unsigned char key);
>>   *   no-snoop                   Disable VT-d Snoop Control
>>   *   no-qinval                  Disable VT-d Queued Invalidation
>>   *   no-intremap                Disable VT-d Interrupt Remapping
>> + *   no-intpost                 Disable VT-d Interrupt posting
>>   */
>>  custom_param("iommu", parse_iommu_param);
>>  bool_t __initdata iommu_enable = 1;
>> @@ -51,6 +52,14 @@ bool_t __read_mostly iommu_passthrough;
>>  bool_t __read_mostly iommu_snoop = 1;
>>  bool_t __read_mostly iommu_qinval = 1;
>>  bool_t __read_mostly iommu_intremap = 1;
>> +
>> +/*
>> + * In the current implementation of VT-d posted interrupts, in some extreme
>> + * cases, the per cpu list which saves the blocked vCPU will be very long,
>> + * and this will affect the interrupt latency, so let this feature off by
>> + * default until we find a good solution to resolve it.
>> + */
>> +bool_t __read_mostly iommu_intpost;
>>  bool_t __read_mostly iommu_hap_pt_share = 1;
>>  bool_t __read_mostly iommu_debug;
>>  bool_t __read_mostly amd_iommu_perdev_intremap = 1;
>> @@ -112,6 +121,9 @@ static void __init parse_iommu_param(char *s)
>>  
>>          s = ss + 1;
>>      } while ( ss );
>> +
>> +    if ( !iommu_intremap )
>> +        iommu_intpost = 0;
> This hunk is still wrong, as I said in v3.

Furthermore, you appear to have no way in v4 to enable intpost on the
Xen command line.

~Andrew

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