From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v2 1/2] VT-d: Reduce spin timeout to 1ms,
 which can be boot-time changed.
Date: Thu, 10 Dec 2015 19:03:00 +0000
Message-ID: <5669CC64.7050407@citrix.com>
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To: Quan Xu <quan.xu@intel.com>, jbeulich@suse.com, kevin.tian@intel.com
Cc: feng.wu@intel.com, george.dunlap@eu.citrix.com, eddie.dong@intel.com, tim@xen.org, xen-devel@lists.xen.org, jun.nakajima@intel.com, keir@xen.org
List-Id: xen-devel@lists.xenproject.org

On 10/12/15 09:33, Quan Xu wrote:
> Signed-off-by: Quan Xu <quan.xu@intel.com>
> ---
>  xen/drivers/passthrough/vtd/qinval.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/xen/drivers/passthrough/vtd/qinval.c b/xen/drivers/passthrough/vtd/qinval.c
> index b81b0bd..990baf2 100644
> --- a/xen/drivers/passthrough/vtd/qinval.c
> +++ b/xen/drivers/passthrough/vtd/qinval.c
> @@ -28,6 +28,11 @@
>  #include "vtd.h"
>  #include "extern.h"
>  
> +static int __read_mostly iommu_qi_timeout_ms = 1;
> +integer_param("iommu_qi_timeout_ms", iommu_qi_timeout_ms);
> +
> +#define IOMMU_QI_TIMEOUT (iommu_qi_timeout_ms * MILLISECS(1))
> +
>  static void print_qi_regs(struct iommu *iommu)
>  {
>      u64 val;
> @@ -167,10 +172,12 @@ static int queue_invalidate_wait(struct iommu *iommu,
>          start_time = NOW();
>          while ( poll_slot != QINVAL_STAT_DONE )
>          {
> -            if ( NOW() > (start_time + DMAR_OPERATION_TIMEOUT) )
> +            if ( NOW() > (start_time + IOMMU_QI_TIMEOUT) )
>              {
>                  print_qi_regs(iommu);
> -                panic("queue invalidate wait descriptor was not executed");
> +                dprintk(XENLOG_WARNING VTDPREFIX,
> +                        "Queue invalidate wait descriptor was timeout.\n");
> +                return -ETIMEDOUT;
>              }
>              cpu_relax();
>          }

This patch misses a second use of DMAR_OPERATION_TIMEOUT, in
IOMMU_WAIT_OP() which in turn is used in a large number of locations. 
All of these locations equally need to be chopped down to a low number
of milliseconds.

~Andrew