linux-pci.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Thomas Gleixner <tglx@linutronix.de>
To: "Raj\, Ashok" <ashok.raj@intel.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	Dan Williams <dan.j.williams@intel.com>, "Tian\,
	Kevin" <kevin.tian@intel.com>, "Jiang\,
	Dave" <dave.jiang@intel.com>, Bjorn Helgaas <helgaas@kernel.org>,
	"vkoul\@kernel.org" <vkoul@kernel.org>, "Dey\,
	Megha" <megha.dey@intel.com>, "maz\@kernel.org" <maz@kernel.org>,
	"bhelgaas\@google.com" <bhelgaas@google.com>,
	"alex.williamson\@redhat.com" <alex.williamson@redhat.com>, "Pan\,
	Jacob jun" <jacob.jun.pan@intel.com>, "Liu\,
	Yi L" <yi.l.liu@intel.com>, "Lu\, Baolu" <baolu.lu@intel.com>,
	"Kumar\, Sanjay K" <sanjay.k.kumar@intel.com>, "Luck\,
	Tony" <tony.luck@intel.com>,
	"kwankhede\@nvidia.com" <kwankhede@nvidia.com>,
	"eric.auger\@redhat.com" <eric.auger@redhat.com>,
	"parav\@mellanox.com" <parav@mellanox.com>,
	"rafael\@kernel.org" <rafael@kernel.org>,
	"netanelg\@mellanox.com" <netanelg@mellanox.com>,
	"shahafs\@mellanox.com" <shahafs@mellanox.com>,
	"yan.y.zhao\@linux.intel.com" <yan.y.zhao@linux.intel.com>,
	"pbonzini\@redhat.com" <pbonzini@redhat.com>, "Ortiz\,
	Samuel" <samuel.ortiz@intel.com>, "Hossain\,
	Mona" <mona.hossain@intel.com>,
	"dmaengine\@vger.kernel.org" <dmaengine@vger.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-pci\@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"kvm\@vger.kernel.org" <kvm@vger.kernel.org>,
	Ashok Raj <ashok.raj@intel.com>
Subject: Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection
Date: Tue, 10 Nov 2020 11:27:29 +0100	[thread overview]
Message-ID: <875z6dik1a.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201110051412.GA20147@otc-nc-03>

Ashok,

On Mon, Nov 09 2020 at 21:14, Ashok Raj wrote:
> On Mon, Nov 09, 2020 at 11:42:29PM +0100, Thomas Gleixner wrote:
>> On Mon, Nov 09 2020 at 13:30, Jason Gunthorpe wrote:
> Approach to IMS is more of a phased approach. 
>
> #1 Allow physical device to scale beyond limits of PCIe MSIx
>    Follows current methodology for guest interrupt programming and
>    evolutionary changes rather than drastic.

Trapping MSI[X] writes is there because it allows to hand a device to an
unmodified guest OS and to handle the case where the MSI[X] entries
storage cannot be mapped exclusively to the guest.

But aside of this, it's not required if the storage can be mapped
exclusively, the guest is hypervisor aware and can get a host composed
message via a hypercall. That works for physical functions and SRIOV,
but not for SIOV.

> #2 Long term we should work together on enabling IMS in guest which
>    requires changes in both HW and SW eco-system.
>
> For #1, the immediate need is to find a way to limit guest from using IMS
> due to current limitations. We have couple options.
>
> a) CPUID based method to disallow IMS when running in a guest OS. Limiting
>    use to existing virtual MSIx to guest devices. (Both you/Jason alluded)
> b) We can extend DMAR table to have a flag for opt-out. So in real platform
>    this flag is clear and in guest VMM will ensure vDMAR will have this flag
>    set. Along the lines as Jason alluded, platform level and via ACPI
>    methods. We have similar use for x2apic_optout today.
>
> Think a) is probably more generic.

But incomplete as I explained before. If the VMM does not set the
hypervisor bit in CPUID then the guest OS assumes to run on bare
metal. It needs more than just relying on CPUID.

Aside of that neither Jason nor myself said that IMS cannot be supported
in a guest. PF and VF IMS can and has to be supported. SIOV is a
different story due to the PASID requirement which obviously needs to be
managed host side and needs HW changes.

> From SW improvements:
>
> - Hypercall to retrieve addr/data from host

You need to have that even for the non SIOV case in order to hand in a
full device which has the IMS storage in queue memory.

> Devices such as idxd that do not have these entries on page-boundaries for
> isolation to permit direct programming from GuestOS will continue to use
> trap-emulate as used today.

That's a restriction of that particular hardware.

> Until then, IMS will be restricted to host VMM only, and we can use the
> methods above to prevent IMS in guest and continue to use the legacy
> virtual MSIx.

SIOV IMS.

But as things stand now not even PF/VF pass through are possible. This
might not be an issue for IDXD, but it's an issue in general and this
want's the be thought of _now_ before we put a lot of infrastructure in
to place which needs then to be ripped apart again.

>> The current specification puts massive restrictions on IMS storage which
>> are _not_ allowing to optimize it in a device specific manner as
>> demonstrated in this discussion.
>
> IMS doesn't restrict this optimization, but to allow it requires more
> OS support as you had mentioned.

Right, IMS per se does not put an restriction on it.

The specification and the HW limitations on the remapping unit put that
restriction into place.

OS support is an obvious requirement, but OS support cannot make
the restrictions of HW go away magically.

But again, we need to think about the path forward _now_.

Just slapping some 'works for IDXD' solution into place can severly
restrict the options for going beyond these limitations simply because
we have to support that 'works for IDXD thing' forever.

Thanks,

        tglx

  reply	other threads:[~2020-11-10 10:27 UTC|newest]

Thread overview: 125+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-30 18:50 [PATCH v4 00/17] Add VFIO mediated device support and DEV-MSI support for the idxd driver Dave Jiang
2020-10-30 18:50 ` [PATCH v4 01/17] irqchip: Add IMS (Interrupt Message Store) driver Dave Jiang
2020-10-30 22:01   ` Thomas Gleixner
2020-10-30 18:51 ` [PATCH v4 02/17] iommu/vt-d: Add DEV-MSI support Dave Jiang
2020-10-30 20:31   ` Thomas Gleixner
2020-10-30 20:52     ` Dave Jiang
2020-10-30 18:51 ` [PATCH v4 03/17] dmaengine: idxd: add theory of operation documentation for idxd mdev Dave Jiang
2020-10-30 18:51 ` [PATCH v4 04/17] dmaengine: idxd: add support for readonly config devices Dave Jiang
2020-10-30 18:51 ` [PATCH v4 05/17] dmaengine: idxd: add interrupt handle request support Dave Jiang
2020-10-30 18:51 ` [PATCH v4 06/17] PCI: add SIOV and IMS capability detection Dave Jiang
2020-10-30 19:51   ` Bjorn Helgaas
2020-10-30 21:20     ` Dave Jiang
2020-10-30 21:50       ` Bjorn Helgaas
2020-10-30 22:45       ` Jason Gunthorpe
2020-10-30 22:49         ` Dave Jiang
2020-11-02 13:21           ` Jason Gunthorpe
2020-11-03  2:49             ` Tian, Kevin
2020-11-03 12:43               ` Jason Gunthorpe
2020-11-04  3:41                 ` Tian, Kevin
2020-11-04 12:40                   ` Jason Gunthorpe
2020-11-04 13:34                     ` Tian, Kevin
2020-11-04 13:54                       ` Jason Gunthorpe
2020-11-06  9:48                         ` Tian, Kevin
2020-11-06 13:14                           ` Jason Gunthorpe
2020-11-06 16:48                             ` Raj, Ashok
2020-11-06 17:51                               ` Jason Gunthorpe
2020-11-06 23:47                                 ` Dan Williams
2020-11-07  0:12                                   ` Jason Gunthorpe
2020-11-07  1:42                                     ` Dan Williams
2020-11-08 18:11                                     ` Raj, Ashok
2020-11-08 18:34                                       ` David Woodhouse
2020-11-08 23:25                                         ` Raj, Ashok
2020-11-10 14:19                                           ` Raj, Ashok
2020-11-10 14:41                                             ` David Woodhouse
2020-11-08 23:41                                       ` Jason Gunthorpe
2020-11-09  0:05                                         ` Raj, Ashok
2020-11-08 18:47                                     ` Thomas Gleixner
2020-11-08 19:36                                       ` David Woodhouse
2020-11-08 22:47                                         ` Thomas Gleixner
2020-11-08 23:29                                           ` Jason Gunthorpe
2020-11-11 15:41                                         ` Christoph Hellwig
2020-11-11 16:09                                           ` Raj, Ashok
2020-11-11 22:27                                             ` Thomas Gleixner
2020-11-11 23:03                                               ` Raj, Ashok
2020-11-12  1:13                                                 ` Thomas Gleixner
2020-11-12 13:10                                                 ` Jason Gunthorpe
2020-11-08 23:23                                       ` Jason Gunthorpe
2020-11-08 23:36                                         ` Raj, Ashok
2020-11-09  7:37                                         ` Tian, Kevin
2020-11-09 16:46                                           ` Jason Gunthorpe
2020-11-08 23:58                                       ` Raj, Ashok
2020-11-09  7:59                                         ` Tian, Kevin
2020-11-09 11:21                                         ` Thomas Gleixner
2020-11-09 17:30                                           ` Jason Gunthorpe
2020-11-09 22:40                                             ` Raj, Ashok
2020-11-09 22:42                                             ` Thomas Gleixner
2020-11-10  5:14                                               ` Raj, Ashok
2020-11-10 10:27                                                 ` Thomas Gleixner [this message]
2020-11-10 14:13                                                   ` Raj, Ashok
2020-11-10 14:23                                                     ` Jason Gunthorpe
2020-11-11  2:17                                                       ` Tian, Kevin
2020-11-12 13:46                                                         ` Jason Gunthorpe
2020-11-11  7:14                                                     ` Tian, Kevin
2020-11-12 19:32                                                       ` Konrad Rzeszutek Wilk
2020-11-12 22:42                                                         ` Thomas Gleixner
2020-11-13  2:42                                                           ` Tian, Kevin
2020-11-13 12:57                                                             ` Jason Gunthorpe
2020-11-13 13:32                                                             ` Thomas Gleixner
2020-11-13 16:12                                                               ` Luck, Tony
2020-11-13 17:38                                                                 ` Raj, Ashok
2020-11-14 10:34                                                           ` Christoph Hellwig
2020-11-14 21:18                                                             ` Raj, Ashok
2020-11-15 11:26                                                               ` Thomas Gleixner
2020-11-15 19:31                                                                 ` Raj, Ashok
2020-11-15 22:11                                                                   ` Thomas Gleixner
2020-11-16  0:22                                                                     ` Raj, Ashok
2020-11-16  7:31                                                                       ` Tian, Kevin
2020-11-16 15:46                                                                         ` Jason Gunthorpe
2020-11-16 17:56                                                                           ` Thomas Gleixner
2020-11-16 18:02                                                                             ` Jason Gunthorpe
2020-11-16 20:37                                                                               ` Thomas Gleixner
2020-11-16 23:51                                                                               ` Tian, Kevin
2020-11-17  9:21                                                                                 ` Thomas Gleixner
2020-11-16  8:25                                                               ` Christoph Hellwig
2020-11-10 14:19                                                 ` Jason Gunthorpe
2020-11-11  2:35                                                   ` Tian, Kevin
2020-11-08 21:18                             ` Thomas Gleixner
2020-11-08 22:09                               ` David Woodhouse
2020-11-08 22:52                                 ` Thomas Gleixner
2020-11-07  0:32                           ` Thomas Gleixner
2020-11-09  5:25                             ` Tian, Kevin
2020-10-30 18:51 ` [PATCH v4 07/17] dmaengine: idxd: add IMS support in base driver Dave Jiang
2020-10-30 18:51 ` [PATCH v4 08/17] dmaengine: idxd: add device support functions in prep for mdev Dave Jiang
2020-10-30 18:51 ` [PATCH v4 09/17] dmaengine: idxd: add basic mdev registration and helper functions Dave Jiang
2020-10-30 18:51 ` [PATCH v4 10/17] dmaengine: idxd: add emulation rw routines Dave Jiang
2020-10-30 18:52 ` [PATCH v4 11/17] dmaengine: idxd: prep for virtual device commands Dave Jiang
2020-10-30 18:52 ` [PATCH v4 12/17] dmaengine: idxd: virtual device commands emulation Dave Jiang
2020-10-30 18:52 ` [PATCH v4 13/17] dmaengine: idxd: ims setup for the vdcm Dave Jiang
2020-10-30 21:26   ` Thomas Gleixner
2020-10-30 18:52 ` [PATCH v4 14/17] dmaengine: idxd: add mdev type as a new wq type Dave Jiang
2020-10-30 18:52 ` [PATCH v4 15/17] dmaengine: idxd: add dedicated wq mdev type Dave Jiang
2020-10-30 18:52 ` [PATCH v4 16/17] dmaengine: idxd: add new wq state for mdev Dave Jiang
2020-10-30 18:52 ` [PATCH v4 17/17] dmaengine: idxd: add error notification from host driver to mediated device Dave Jiang
2020-10-30 18:58 ` [PATCH v4 00/17] Add VFIO mediated device support and DEV-MSI support for the idxd driver Jason Gunthorpe
2020-10-30 19:13   ` Dave Jiang
2020-10-30 19:17     ` Jason Gunthorpe
2020-10-30 19:23       ` Raj, Ashok
2020-10-30 19:30         ` Jason Gunthorpe
2020-10-30 20:43           ` Raj, Ashok
2020-10-30 22:54             ` Jason Gunthorpe
2020-10-31  2:50             ` Thomas Gleixner
2020-10-31 23:53               ` Raj, Ashok
2020-11-02 13:20                 ` Jason Gunthorpe
2020-11-02 16:20                   ` Raj, Ashok
2020-11-02 17:19                     ` Jason Gunthorpe
2020-11-02 18:18                       ` Dave Jiang
2020-11-02 18:26                         ` Jason Gunthorpe
2020-11-02 18:38                           ` Dan Williams
2020-11-02 18:51                             ` Jason Gunthorpe
2020-11-02 19:26                               ` Dan Williams
2020-10-30 20:48 ` Thomas Gleixner
2020-10-30 20:59   ` Dave Jiang
2020-10-30 22:10     ` Thomas Gleixner
     [not found] <draft-875z6ekcj5.fsf@nanos.tec.linutronix.de>
2020-11-09 14:08 ` [PATCH v4 06/17] PCI: add SIOV and IMS capability detection Thomas Gleixner
2020-11-09 18:10   ` Raj, Ashok

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=875z6dik1a.fsf@nanos.tec.linutronix.de \
    --to=tglx@linutronix.de \
    --cc=alex.williamson@redhat.com \
    --cc=ashok.raj@intel.com \
    --cc=baolu.lu@intel.com \
    --cc=bhelgaas@google.com \
    --cc=dan.j.williams@intel.com \
    --cc=dave.jiang@intel.com \
    --cc=dmaengine@vger.kernel.org \
    --cc=eric.auger@redhat.com \
    --cc=helgaas@kernel.org \
    --cc=jacob.jun.pan@intel.com \
    --cc=jgg@nvidia.com \
    --cc=kevin.tian@intel.com \
    --cc=kvm@vger.kernel.org \
    --cc=kwankhede@nvidia.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=maz@kernel.org \
    --cc=megha.dey@intel.com \
    --cc=mona.hossain@intel.com \
    --cc=netanelg@mellanox.com \
    --cc=parav@mellanox.com \
    --cc=pbonzini@redhat.com \
    --cc=rafael@kernel.org \
    --cc=samuel.ortiz@intel.com \
    --cc=sanjay.k.kumar@intel.com \
    --cc=shahafs@mellanox.com \
    --cc=tony.luck@intel.com \
    --cc=vkoul@kernel.org \
    --cc=yan.y.zhao@linux.intel.com \
    --cc=yi.l.liu@intel.com \
    --subject='Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
on how to clone and mirror all data and code used for this inbox