QEMU-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: Bharat Bhushan <bharatb.linux@gmail.com>
To: Auger Eric <eric.auger@redhat.com>
Cc: "yang.zhong@intel.com" <yang.zhong@intel.com>,
	"peter.maydell@linaro.org" <peter.maydell@linaro.org>,
	"kevin.tian@intel.com" <kevin.tian@intel.com>,
	"Tomasz Nowicki \[C\]" <tnowicki@marvell.com>,
	"mst@redhat.com" <mst@redhat.com>,
	"drjones@redhat.com" <drjones@redhat.com>,
	"peterx@redhat.com" <peterx@redhat.com>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	Alex Williamson <alex.williamson@redhat.com>,
	"qemu-arm@nongnu.org" <qemu-arm@nongnu.org>,
	"jean-philippe@linaro.org" <jean-philippe@linaro.org>,
	Bharat Bhushan <bbhushan2@marvell.com>,
	"eric.auger.pro@gmail.com" <eric.auger.pro@gmail.com>,
	"linuc.decode@gmail.com" <linuc.decode@gmail.com>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [EXT] Re: [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio region translation by viommu
Date: Tue, 5 May 2020 14:55:06 +0530
Message-ID: <CAAeCc_nnE2FBo2wW+NkJX-vOP3FF_wSvLg0KngND4HhFUAGf9Q@mail.gmail.com> (raw)
In-Reply-To: <72e3ea5c-c98c-3e02-26d1-b956ee81e30f@redhat.com>

Hi Eric,

On Fri, Apr 24, 2020 at 7:47 PM Auger Eric <eric.auger@redhat.com> wrote:
>
> Hi Bharat,
>
> On 4/2/20 11:01 AM, Bharat Bhushan wrote:
> > Hi Eric/Alex,
> >
> >> -----Original Message-----
> >> From: Alex Williamson <alex.williamson@redhat.com>
> >> Sent: Thursday, March 26, 2020 11:23 PM
> >> To: Auger Eric <eric.auger@redhat.com>
> >> Cc: Bharat Bhushan <bbhushan2@marvell.com>; peter.maydell@linaro.org;
> >> peterx@redhat.com; eric.auger.pro@gmail.com; kevin.tian@intel.com;
> >> mst@redhat.com; Tomasz Nowicki [C] <tnowicki@marvell.com>;
> >> drjones@redhat.com; linuc.decode@gmail.com; qemu-devel@nongnu.org; qemu-
> >> arm@nongnu.org; bharatb.linux@gmail.com; jean-philippe@linaro.org;
> >> yang.zhong@intel.com; David Gibson <david@gibson.dropbear.id.au>
> >> Subject: [EXT] Re: [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio
> >> region translation by viommu
> >>
> >> External Email
> >>
> >> ----------------------------------------------------------------------
> >> On Thu, 26 Mar 2020 18:35:48 +0100
> >> Auger Eric <eric.auger@redhat.com> wrote:
> >>
> >>> Hi Alex,
> >>>
> >>> On 3/24/20 12:08 AM, Alex Williamson wrote:
> >>>> [Cc +dwg who originated this warning]
> >>>>
> >>>> On Mon, 23 Mar 2020 14:16:09 +0530
> >>>> Bharat Bhushan <bbhushan2@marvell.com> wrote:
> >>>>
> >>>>> On ARM, the MSI doorbell is translated by the virtual IOMMU.
> >>>>> As such address_space_translate() returns the MSI controller MMIO
> >>>>> region and we get an "iommu map to non memory area"
> >>>>> message. Let's remove this latter.
> >>>>>
> >>>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> >>>>> Signed-off-by: Bharat Bhushan <bbhushan2@marvell.com>
> >>>>> ---
> >>>>>  hw/vfio/common.c | 2 --
> >>>>>  1 file changed, 2 deletions(-)
> >>>>>
> >>>>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c index
> >>>>> 5ca11488d6..c586edf47a 100644
> >>>>> --- a/hw/vfio/common.c
> >>>>> +++ b/hw/vfio/common.c
> >>>>> @@ -426,8 +426,6 @@ static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb,
> >> void **vaddr,
> >>>>>                                   &xlat, &len, writable,
> >>>>>                                   MEMTXATTRS_UNSPECIFIED);
> >>>>>      if (!memory_region_is_ram(mr)) {
> >>>>> -        error_report("iommu map to non memory area %"HWADDR_PRIx"",
> >>>>> -                     xlat);
> >>>>>          return false;
> >>>>>      }
> >>>>>
> >>>>
> >>>> I'm a bit confused here, I think we need more justification beyond
> >>>> "we hit this warning and we don't want to because it's ok in this
> >>>> one special case, therefore remove it".  I assume the special case
> >>>> is that the device MSI address is managed via the SET_IRQS ioctl and
> >>>> therefore we won't actually get DMAs to this range.
> >>> Yes exactly. The guest creates a mapping between one giova and this
> >>> gpa (corresponding to the MSI controller doorbell) because MSIs are
> >>> mapped on ARM. But practically the physical device is programmed with
> >>> an host chosen iova that maps onto the physical MSI controller's
> >>> doorbell. so the device never performs DMA accesses to this range.
> >>>
> >>>   But I imagine the case that
> >>>> was in mind when adding this warning was general peer-to-peer
> >>>> between and assigned and emulated device.
> >>> yes makes sense.
> >>>
> >>>   Maybe there's an argument to be made
> >>>> that such a p2p mapping might also be used in a non-vIOMMU case.  We
> >>>> skip creating those mappings and drivers continue to work, maybe
> >>>> because nobody attempts to do p2p DMA with the types of devices we
> >>>> emulate, maybe because p2p DMA is not absolutely reliable on bare
> >>>> metal and drivers test it before using it.
> >>> MSI doorbells are mapped using the IOMMU_MMIO flag (dma-iommu.c
> >>> iommu_dma_get_msi_page).
> >>> One idea could be to pass that flag through the IOMMU Notifier
> >>> mechanism into the iotlb->perm. Eventually when we get this in
> >>> vfio_get_vaddr() we would not print the warning. Could that make sense?
> >>
> >> Yeah, if we can identify a valid case that doesn't need a warning, that's fine by me.
> >> Thanks,
> >
> > Let me know if I understood the proposal correctly:
> >
> > virtio-iommu driver in guest will make map (VIRTIO_IOMMU_T_MAP) with VIRTIO_IOMMU_MAP_F_MMIO flag for MSI mapping.
> > In qemu, virtio-iommu device will set a new defined flag (say IOMMU_MMIO) in iotlb->perm in memory_region_notify_iommu(). vfio_get_vaddr() will check same flag and will not print the warning.>
> > Is above correct?
> Yes that's what I had in mind.

In that case virtio-iommu driver in guest should not make map
(VIRTIO_IOMMU_T_MAP) call as it known nothing to be mapped.

Stay Safe

Thanks
-Bharat

>
> Thanks
>
> Eric
> >
> > Thanks
> > -Bharat
> >
> >>
> >> Alex
> >
> >
>


  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-23  8:46 [PATCH v9 0/9] virtio-iommu: VFIO integration Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio region translation by viommu Bharat Bhushan
2020-03-23 23:08   ` Alex Williamson
2020-03-26 17:35     ` Auger Eric
2020-03-26 17:53       ` Alex Williamson
2020-03-27  5:50         ` [EXT] " Bharat Bhushan
2020-04-02  9:01         ` Bharat Bhushan
2020-04-24 14:17           ` Auger Eric
2020-05-05  9:25             ` Bharat Bhushan [this message]
2020-05-05  9:30               ` Auger Eric
2020-05-05  9:46                 ` Bharat Bhushan
2020-05-05 10:18                   ` Bharat Bhushan
2020-05-05 12:05                     ` Auger Eric
2020-05-07 14:40                     ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 2/9] memory: Add interface to set iommu page size mask Bharat Bhushan
2020-03-26 16:06   ` Auger Eric
2020-03-27  5:33     ` [EXT] " Bharat Bhushan
2020-03-27  8:27       ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 3/9] vfio: set iommu page size as per host supported page size Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 4/9] virtio-iommu: set supported page size mask Bharat Bhushan
2020-03-26 15:51   ` Auger Eric
2020-03-27  5:13     ` [EXT] " Bharat Bhushan
2020-03-27  8:28       ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 5/9] virtio-iommu: Add iommu notifier for map/unmap Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 6/9] virtio-iommu: Call iommu notifier for attach/detach Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 7/9] virtio-iommu: add iommu replay Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 8/9] virtio-iommu: Implement probe request Bharat Bhushan
2020-03-26 15:48   ` Auger Eric
2020-03-27  5:40     ` [EXT] " Bharat Bhushan
2020-03-27  8:34       ` Auger Eric
2020-04-23 16:09   ` Jean-Philippe Brucker
2020-04-24 13:51     ` Auger Eric
2020-05-05  9:06       ` Bharat Bhushan
2020-05-07 14:42         ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 9/9] virtio-iommu: add iommu notifier memory-region Bharat Bhushan
2020-03-23  9:52 ` [PATCH v9 0/9] virtio-iommu: VFIO integration no-reply
2020-03-23  9:59 ` no-reply

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=CAAeCc_nnE2FBo2wW+NkJX-vOP3FF_wSvLg0KngND4HhFUAGf9Q@mail.gmail.com \
    --to=bharatb.linux@gmail.com \
    --cc=alex.williamson@redhat.com \
    --cc=bbhushan2@marvell.com \
    --cc=david@gibson.dropbear.id.au \
    --cc=drjones@redhat.com \
    --cc=eric.auger.pro@gmail.com \
    --cc=eric.auger@redhat.com \
    --cc=jean-philippe@linaro.org \
    --cc=kevin.tian@intel.com \
    --cc=linuc.decode@gmail.com \
    --cc=mst@redhat.com \
    --cc=peter.maydell@linaro.org \
    --cc=peterx@redhat.com \
    --cc=qemu-arm@nongnu.org \
    --cc=qemu-devel@nongnu.org \
    --cc=tnowicki@marvell.com \
    --cc=yang.zhong@intel.com \
    /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

QEMU-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/qemu-devel/0 qemu-devel/git/0.git
	git clone --mirror https://lore.kernel.org/qemu-devel/1 qemu-devel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 qemu-devel qemu-devel/ https://lore.kernel.org/qemu-devel \
		qemu-devel@nongnu.org
	public-inbox-index qemu-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.nongnu.qemu-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git