From: Jason Wang <jasowang@redhat.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>,
linux-s390@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
Christian Borntraeger <borntraeger@de.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Viktor Mihajlovski <mihajlov@linux.ibm.com>,
Cornelia Huck <cohuck@redhat.com>, Ram Pai <linuxram@us.ibm.com>,
Thiago Jung Bauermann <bauerman@linux.ibm.com>,
David Gibson <david@gibson.dropbear.id.au>,
"Lendacky, Thomas" <Thomas.Lendacky@amd.com>,
Michael Mueller <mimu@linux.ibm.com>
Subject: Re: [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM
Date: Tue, 25 Feb 2020 11:30:16 +0800 [thread overview]
Message-ID: <1b2673e7-56ff-7d69-af2d-503a97408d95@redhat.com> (raw)
In-Reply-To: <20200224145607.2729f47b.pasic@linux.ibm.com>
On 2020/2/24 下午9:56, Halil Pasic wrote:
> On Mon, 24 Feb 2020 17:26:20 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>> That's better.
>>
>> How about attached?
>>
>> Thanks
> Thanks Jason! It does avoid the translation overhead in vhost.
>
> Tested-by: Halil Pasic <pasic@linux.ibm.com>
>
> Regarding the code, you fence it in virtio-net.c, but AFAIU this feature
> has relevance for other vhost devices as well. E.g. what about vhost
> user? Would it be the responsibility of each virtio device to fence this
> on its own?
Yes, it looks to me it's better to do that in virtio_set_features_nocheck()
>
> I'm also a bit confused about the semantics of the vhost feature bit
> F_ACCESS_PLATFORM. What we have specified on virtio level is:
> """
> This feature indicates that the device can be used on a platform where
> device access to data in memory is limited and/or translated. E.g. this
> is the case if the device can be located behind an IOMMU that translates
> bus addresses from the device into physical addresses in memory, if the
> device can be limited to only access certain memory addresses or if
> special commands such as a cache flush can be needed to synchronise data
> in memory with the device. Whether accesses are actually limited or
> translated is described by platform-specific means. If this feature bit
> is set to 0, then the device has same access to memory addresses
> supplied to it as the driver has. In particular, the device will always
> use physical addresses matching addresses used by the driver (typically
> meaning physical addresses used by the CPU) and not translated further,
> and can access any address supplied to it by the driver. When clear,
> this overrides any platform-specific description of whether device
> access is limited or translated in any way, e.g. whether an IOMMU may be
> present.
> """
>
> I read this like the addresses may be IOVAs which require
> IMMU translation or GPAs which don't.
>
> On the vhost level however, it seems that F_IOMMU_PLATFORM means that
> vhost has to do the translation (via IOTLB API).
Yes.
>
> Do I understand this correctly? If yes, I believe we should document
> this properly.
Good point. I think it was probably wrong to tie F_IOMMU_PLATFORM to
IOTLB API. Technically IOTLB can work with GPA->HVA mapping. I
originally use a dedicated feature bit (you can see that from commit
log), but for some reason Michael tweak it to virtio feature bit. I
guess it was probably because at that time there's no way to specify e.g
backend capability but now we have VHOST_GET_BACKEND_FEATURES.
For now, it was probably too late to fix that but document or we can add
the support of enabling IOTLB via new backend features.
>
> BTW I'm still not 100% on the purpose and semantics of the
> F_ACCESS_PLATFORM feature bit. But that is a different problem.
Yes, I aggree that we should decouple the features that does not belongs
to device (protected, encrypted, swiotlb etc) from F_IOMMU_PLATFORM. But
Michael and other have their points as well.
Thanks
>
> Regards,
> Halil
>
prev parent reply other threads:[~2020-02-25 3:30 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-20 16:06 [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM Halil Pasic
2020-02-20 16:06 ` [PATCH 1/2] mm: move force_dma_unencrypted() to mem_encrypt.h Halil Pasic
2020-02-20 16:11 ` Christoph Hellwig
2020-02-20 16:23 ` Christian Borntraeger
2020-02-20 16:31 ` Christoph Hellwig
2020-02-20 17:00 ` Christian Borntraeger
2020-02-21 3:27 ` David Gibson
2020-02-21 13:06 ` Halil Pasic
2020-02-21 15:48 ` Michael S. Tsirkin
2020-02-21 18:07 ` Halil Pasic
2020-02-24 3:33 ` David Gibson
2020-02-24 18:49 ` Halil Pasic
2020-02-25 18:08 ` Cornelia Huck
2020-02-28 0:23 ` David Gibson
2020-02-20 16:06 ` [PATCH 2/2] virtio: let virtio use DMA API when guest RAM is protected Halil Pasic
2020-02-20 16:13 ` Christoph Hellwig
2020-02-21 2:59 ` David Gibson
2020-02-21 3:41 ` Jason Wang
2020-02-21 13:31 ` Halil Pasic
2020-02-21 13:27 ` Halil Pasic
2020-02-21 16:36 ` Christoph Hellwig
2020-02-24 6:50 ` David Gibson
2020-02-24 18:59 ` Halil Pasic
2020-02-21 14:33 ` Halil Pasic
2020-02-21 16:39 ` Christoph Hellwig
2020-02-21 18:16 ` Halil Pasic
2020-02-22 19:07 ` Michael S. Tsirkin
2020-02-24 17:16 ` Christoph Hellwig
[not found] ` <691d8c8e-665c-b05f-383f-78377fcf6741@amazon.com>
2020-10-28 18:01 ` Michael S. Tsirkin
2020-02-20 20:55 ` Michael S. Tsirkin
2020-02-21 1:17 ` Ram Pai
2020-02-21 3:29 ` David Gibson
2020-02-21 13:12 ` Halil Pasic
2020-02-21 15:39 ` Tom Lendacky
2020-02-24 6:40 ` David Gibson
2020-02-21 15:56 ` Michael S. Tsirkin
2020-02-21 16:35 ` Christoph Hellwig
2020-02-21 18:03 ` Halil Pasic
2020-02-20 20:48 ` [PATCH 0/2] virtio: decouple protected guest RAM form VIRTIO_F_IOMMU_PLATFORM Michael S. Tsirkin
2020-02-20 21:29 ` Michael S. Tsirkin
2020-02-21 13:37 ` Halil Pasic
2020-02-20 21:33 ` Michael S. Tsirkin
2020-02-21 13:49 ` Halil Pasic
2020-02-21 16:41 ` Christoph Hellwig
2020-02-24 5:44 ` David Gibson
2020-02-21 6:22 ` Jason Wang
2020-02-21 14:56 ` Halil Pasic
2020-02-24 3:38 ` David Gibson
2020-02-24 4:01 ` Jason Wang
2020-02-24 6:06 ` Michael S. Tsirkin
2020-02-24 6:45 ` Jason Wang
2020-02-24 7:48 ` Michael S. Tsirkin
2020-02-24 9:26 ` Jason Wang
2020-02-24 13:40 ` Michael S. Tsirkin
2020-02-25 3:38 ` Jason Wang
2020-02-24 13:56 ` Halil Pasic
2020-02-25 3:30 ` Jason Wang [this message]
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