Re: [Qemu-devel] [PATCH] intel_iommu: relax iq tail check on VTD_GCMD_QIE enable

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jun 16, 2017 at 01:44:43PM +0200, Ladi Prosek wrote:
> The VT-d spec (section 6.5.2) prescribes software to zero the
> Invalidation Queue Tail Register before enabling the VTD_GCMD_QIE
> Global Command Register bit. Windows Server 2012 R2 and possibly
> other older Windows versions violate the protocol and set a
> non-zero queue tail first, which in effect makes them crash early
> on boot with -device intel-iommu,intremap=on.
> 
> This commit relaxes the check and instead of failing to enable
> VTD_GCMD_QIE with "error: can't enable Queued Invalidation", it
> behaves as if the tail register was set just after enabling
> VTD_GCMD_QIE (see vtd_handle_iqt_write).
> 
> Signed-off-by: Ladi Prosek <lprosek@redhat.com>

Thanks!
This conflicts with Peter's tracing which I merged -
could you rework on top of that pls?
the new warning should be a trace point too I imagine.

> ---
>  hw/i386/intel_iommu.c | 32 +++++++++++++++-----------------
>  1 file changed, 15 insertions(+), 17 deletions(-)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 15610b9..f2cb822 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -1466,10 +1466,7 @@ static uint64_t vtd_iotlb_flush(IntelIOMMUState *s, uint64_t val)
>      return iaig;
>  }
>  
> -static inline bool vtd_queued_inv_enable_check(IntelIOMMUState *s)
> -{
> -    return s->iq_tail == 0;
> -}
> +static void vtd_fetch_inv_desc(IntelIOMMUState *s);
>  
>  static inline bool vtd_queued_inv_disable_check(IntelIOMMUState *s)
>  {
> @@ -1483,19 +1480,20 @@ static void vtd_handle_gcmd_qie(IntelIOMMUState *s, bool en)
>  
>      VTD_DPRINTF(INV, "Queued Invalidation Enable %s", (en ? "on" : "off"));
>      if (en) {
> -        if (vtd_queued_inv_enable_check(s)) {
> -            s->iq = iqa_val & VTD_IQA_IQA_MASK;
> -            /* 2^(x+8) entries */
> -            s->iq_size = 1UL << ((iqa_val & VTD_IQA_QS) + 8);
> -            s->qi_enabled = true;
> -            VTD_DPRINTF(INV, "DMAR_IQA_REG 0x%"PRIx64, iqa_val);
> -            VTD_DPRINTF(INV, "Invalidation Queue addr 0x%"PRIx64 " size %d",
> -                        s->iq, s->iq_size);
> -            /* Ok - report back to driver */
> -            vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_QIES);
> -        } else {
> -            VTD_DPRINTF(GENERAL, "error: can't enable Queued Invalidation: "
> -                        "tail %"PRIu16, s->iq_tail);
> +        s->iq = iqa_val & VTD_IQA_IQA_MASK;
> +        /* 2^(x+8) entries */
> +        s->iq_size = 1UL << ((iqa_val & VTD_IQA_QS) + 8);
> +        s->qi_enabled = true;
> +        VTD_DPRINTF(INV, "DMAR_IQA_REG 0x%"PRIx64, iqa_val);
> +        VTD_DPRINTF(INV, "Invalidation Queue addr 0x%"PRIx64 " size %d",
> +                    s->iq, s->iq_size);
> +        /* Ok - report back to driver */
> +        vtd_set_clear_mask_long(s, DMAR_GSTS_REG, 0, VTD_GSTS_QIES);
> +
> +        if (s->iq_tail != 0 &&
> +            !(vtd_get_long_raw(s, DMAR_FSTS_REG) & VTD_FSTS_IQE)) {
> +            VTD_DPRINTF(INV, "warning: QI enabled with non-zero tail");
> +            vtd_fetch_inv_desc(s);
>          }
>      } else {
>          if (vtd_queued_inv_disable_check(s)) {
> -- 
> 2.9.3