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Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capabili
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest |
Date: |
Thu, 2 Jun 2016 07:00:46 -0600 |
On Thu, 2 Jun 2016 16:44:39 +0800
Peter Xu <address@hidden> wrote:
> On Sat, May 21, 2016 at 06:42:03PM +0200, Jan Kiszka wrote:
> > On 2016-05-21 18:19, Aviv B.D wrote:
> > > From: "Aviv Ben-David" <address@hidden>
> > >
> > > This flag tells the guest to invalidate tlb cache also after unmap
> > > operations.
> > >
> > > Signed-off-by: Aviv Ben-David <address@hidden>
> > > ---
> > > hw/i386/intel_iommu.c | 3 ++-
> > > hw/i386/intel_iommu_internal.h | 1 +
> > > 2 files changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> > > index 347718f..1af8da8 100644
> > > --- a/hw/i386/intel_iommu.c
> > > +++ b/hw/i386/intel_iommu.c
> > > @@ -1949,7 +1949,8 @@ static void vtd_init(IntelIOMMUState *s)
> > > s->iq_last_desc_type = VTD_INV_DESC_NONE;
> > > s->next_frcd_reg = 0;
> > > s->cap = VTD_CAP_FRO | VTD_CAP_NFR | VTD_CAP_ND | VTD_CAP_MGAW |
> > > - VTD_CAP_SAGAW | VTD_CAP_MAMV | VTD_CAP_PSI | VTD_CAP_SLLPS;
> > > + VTD_CAP_SAGAW | VTD_CAP_MAMV | VTD_CAP_PSI | VTD_CAP_SLLPS |
> > > + VTD_CAP_CM;
> >
> > Again, needs to be optional because not all guests will support it or
> > behave differently when it's set (I've one that refuses to work).
>
> There should be more than one way to make it optional. Which is
> better? What I can think of:
>
> (Assume we have Marcel's "-device intel_iommu" working already)
>
> 1. Let the CM bit optional, or say, we need to specify something like
> "-device intel_iommu,cmbit=on" or we will disable CM bit. If we
> have CM disabled but with VFIO device, let QEMU raise error.
>
> 2. We automatically detect whether we need CM bit. E.g., if we have
> VFIO and vIOMMU both enabled, we automatically set the bit. Another
> case is maybe we would in the future support nested vIOMMU? If so,
> we can do the same thing for the nested feature.
Why do we need to support VT-d for guests that do not support CM=1?
The VT-d spec indicates that software should be written to handle both
caching modes (6.1). Granted this is a *should* and not a *must*,
but can't we consider guests that do not support CM=1 incompatible with
emulated VT-d? If CM=0 needs to be supported then we need to shadow
all of the remapping structures since vfio effectively becomes a cache
of the that would otherwise depend on the invalidation of both present
and non-present entries. What guests do not support CM=1? Thanks,
Alex
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Peter Xu, 2016/06/02
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest,
Alex Williamson <=
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Jan Kiszka, 2016/06/02
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Jan Kiszka, 2016/06/02
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Michael S. Tsirkin, 2016/06/02
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Peter Xu, 2016/06/06
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Alex Williamson, 2016/06/06
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Peter Xu, 2016/06/06
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Alex Williamson, 2016/06/06
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Peter Xu, 2016/06/06
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Alex Williamson, 2016/06/06
- Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest, Peter Xu, 2016/06/07