Re: [Qemu-devel] [PATCH v3 0/2] intel-iommu: add support for 5-level virtual IOMMU.

[Yu Zhang]

On Mon, Jan 14, 2019 at 11:02:28PM -0500, Michael S. Tsirkin wrote:
> On Wed, Dec 12, 2018 at 09:05:37PM +0800, Yu Zhang wrote:
> > Intel's upcoming processors will extend maximum linear address width to
> > 57 bits, and introduce 5-level paging for CPU. Meanwhile, the platform
> > will also extend the maximum guest address width for IOMMU to 57 bits,
> > thus introducing the 5-level paging for 2nd level translation(See chapter
> > 3 in Intel Virtualization Technology for Directed I/O). 
> > 
> > This patch series extends the current logic to support a wider address 
> > width.
> > A 5-level paging capable IOMMU(for 2nd level translation) can be rendered
> > with configuration "device intel-iommu,x-aw-bits=57".
> > 
> > Also, kvm-unit-tests were updated to verify this patch series. Patch for
> > the test was sent out at: https://www.spinics.net/lists/kvm/msg177425.html.
> > 
> > Note: this patch series checks the existance of 5-level paging in the host
> > and in the guest, and rejects configurations for 57-bit IOVA if either check
> > fails(VTD-d hardware shall not support 57-bit IOVA on platforms without CPU
> > 5-level paging). However, current vIOMMU implementation still lacks logic to
> > check against the physical IOMMU capability, future enhancements are 
> > expected
> > to do this.
> > 
> > Changes in V3: 
> > - Address comments from Peter Xu: squash the 3rd patch in v2 into the 2nd
> >   patch in this version.
> > - Added "Reviewed-by: Peter Xu <address@hidden>"
> > 
> > Changes in V2: 
> > - Address comments from Peter Xu: add haw member in vtd_page_walk_info.
> > - Address comments from Peter Xu: only searches for 4K/2M/1G mappings in
> > iotlb are meaningful. 
> > - Address comments from Peter Xu: cover letter changes(e.g. mention the test
> > patch in kvm-unit-tests).
> > - Coding style changes.
> > ---
> > Cc: "Michael S. Tsirkin" <address@hidden> 
> > Cc: Igor Mammedov <address@hidden> 
> > Cc: Marcel Apfelbaum <address@hidden>
> > Cc: Paolo Bonzini <address@hidden> 
> > Cc: Richard Henderson <address@hidden> 
> > Cc: Eduardo Habkost <address@hidden>
> > Cc: Peter Xu <address@hidden>
> 
> 
> OK is this going anywhere?
> How about dropping cpu flags probing for now, you can
> always revisit it later.
> Will make it maybe a bit less user friendly but OTOH
> uncontriversial...

Thanks Michael, and sorry for the late reply.

Sure. For patch 2/2, I'd like to drop the cpu check.

And we are working on another patch to check the host capability.
This is supposed to be done by sysfs similar to Peter's previous
suggestion. One exception is that our plan is to use the minimal
capability of all host VT-d hardware. For example, allow 4-level
vIOMMU as long as there is a VT-d hardware do not support 5-level,
in case we offered a 5-level vIOMMU, yet to find later a hotplugged
device is binded to a 4-level VT-d hardware. This patch is not ready
yet, because we also would like to cover the requirement of scalable
mode. So for now, I'm more inclined to just drop the cpu check and
add some TODO comments.

And as to 1/2, I am proposing to address the initialization problem
by resetting the haw in vIOMMU in pc_machine_done() in my another
reply. If you are OK with this direction, I'll send out the patch after
testing. :-)

B.R.
Yu

> 
> > ---
> > 
> > Yu Zhang (2):
> >   intel-iommu: differentiate host address width from IOVA address width.
> >   intel-iommu: extend VTD emulation to allow 57-bit IOVA address width.
> > 
> >  hw/i386/acpi-build.c           |  2 +-
> >  hw/i386/intel_iommu.c          | 96 
> > +++++++++++++++++++++++++++++-------------
> >  hw/i386/intel_iommu_internal.h | 10 ++++-
> >  include/hw/i386/intel_iommu.h  | 10 +++--
> >  4 files changed, 81 insertions(+), 37 deletions(-)
> > 
> > -- 
> > 1.9.1
>