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From: Thomas Gleixner <tglx@linutronix.de>
To: "Raj\, Ashok" <ashok.raj@intel.com>,
	Christoph Hellwig <hch@infradead.org>
Cc: David Woodhouse <dwmw2@infradead.org>,
	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>,
	"jing.lin\@intel.com" <jing.lin@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: Wed, 11 Nov 2020 23:27:28 +0100	[thread overview]
Message-ID: <87k0uro7fz.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201111160922.GA83266@otc-nc-03>

On Wed, Nov 11 2020 at 08:09, Ashok Raj wrote:
> On Wed, Nov 11, 2020 at 03:41:59PM +0000, Christoph Hellwig wrote:
>> On Sun, Nov 08, 2020 at 07:36:34PM +0000, David Woodhouse wrote:
>> > So it does look like we're going to need a hypercall interface to
>> > compose an MSI message on behalf of the guest, for IMS to use. In fact
>> > PCI devices assigned to a guest could use that too, and then we'd only
>> > need to trap-and-remap any attempt to write a Compatibility Format MSI
>> > to the device's MSI table, while letting Remappable Format messages get
>> > written directly.
>> > 
>> > We'd also need a way for an OS running on bare metal to *know* that
>> > it's on bare metal and can just compose MSI messages for itself. Since
>> > we do expect bare metal to have an IOMMU, perhaps that is just a
>> > feature flag on the IOMMU?
>> 
>> Have the platform firmware advertise if it needs native or virtualized
>> IMS handling.  If it advertises neither don't support IMS?
>
> The platform hint can be easily accomplished via DMAR table flags. We could
> have an IMS_OPTOUT(similart to x2apic optout flag) flag, when 0 its native 
> and IMS is supported.
>
> When vIOMMU is presented to guest, virtual DMAR table will have this flag
> set to 1. Indicates to GuestOS, native IMS isn't supported.

These opt-out bits suck by definition. It comes all back to the fact
that the whole virt thing didn't have a hardware defined way to tell
that the OS runs in a VM and not on bare metal. It wouldn't have been
rocket science to do so.

And because that does not exist, we need magic opt-out bits for every
other piece of functionality which gets added. Can we please stop this
and provide a well defined way to tell the OS whether it runs on bare
metal or not?

The point is that you really want opt-in bits so that decisions come
down to

     if (!virt || virt->supports_X)

which is the obvious sane and safe logic. But sure, why am I asking for
sane and safe in the context of virtualization?

Thanks,

        tglx

  reply	other threads:[~2020-11-12  2:05 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 [this message]
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
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

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