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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, shahafs@mellanox.com
Subject: Re: [PATCH V2 02/14] virtio-pci: switch to use devres for modern devices
Date: Fri, 27 Nov 2020 10:54:14 +0800	[thread overview]
Message-ID: <9638da54-394c-98f1-ad0e-12f3f0ddf17e@redhat.com> (raw)
In-Reply-To: <20201126084708-mutt-send-email-mst@kernel.org>


On 2020/11/26 下午9:57, Michael S. Tsirkin wrote:
> On Thu, Nov 26, 2020 at 05:25:52PM +0800, Jason Wang wrote:
>> This patch tries to convert the modern device to use devres to manage
>> its resources (iomaps). Before this patch the IO address is mapped
>> individually according to the capability. After this patch, we simply
>> map the whole BAR.
> I think the point of mapping capability was e.g. for devices with
> huge BARs. We don't want to waste virtual memory for e.g. 32 bit guests.
>
> And in particular the spec says:
>
> 	The drivers SHOULD only map part of configuration structure large enough for device operation. The drivers
> 	MUST handle an unexpectedly large length, but MAY check that length is large enough for device operation.


Good point, so I will stick to devres but not use the shortcut like 
whole BAR mapping.


>
> I also wonder how would this interact with cases where device memory is
> mapped for different reasons, such as for MSI table access, into userspace
> as it has resources such as virtio mem, etc.


I think it depends on the driver, e.g for virtio-pci and vDPA, the upper 
layer driver (virtio bus or vDPA bus) know nothing about transport 
specific thing. It should be ok.


> E.g. don't e.g. intel CPUs disallow mapping the same address twice
> with different attributes?


Do you mean it doesn't allow one VA is mapped as UC but the other is 
not? I don't know. But anyhow my understanding is that 
virtio-pci/vp_vdpa tries to hide the details so we can not have two 
mappings here.

Thanks


>


  reply	other threads:[~2020-11-27  2:54 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-26  9:25 [PATCH V2 00/14] vDPA driver for virtio-pci device Jason Wang
2020-11-26  9:25 ` [PATCH V2 01/14] virtio-pci: do not access iomem via virtio_pci_device directly Jason Wang
2020-11-26 13:46   ` Michael S. Tsirkin
2020-11-27  2:50     ` Jason Wang
2020-11-26  9:25 ` [PATCH V2 02/14] virtio-pci: switch to use devres for modern devices Jason Wang
2020-11-26 13:57   ` Michael S. Tsirkin
2020-11-27  2:54     ` Jason Wang [this message]
2020-11-26  9:25 ` [PATCH V2 03/14] virtio-pci: split out modern device Jason Wang
2020-11-26  9:25 ` [PATCH V2 04/14] virtio-pci: move the notification sanity check to vp_modern_probe() Jason Wang
2020-11-26  9:25 ` [PATCH V2 05/14] virtio-pci-modern: introduce vp_modern_set_queue_vector() Jason Wang
2020-11-26  9:25 ` [PATCH V2 06/14] virtio-pci-modern: introduce vp_modern_queue_address() Jason Wang
2020-11-26  9:25 ` [PATCH V2 07/14] virtio-pci-modern: introduce helper to set/get queue_enable Jason Wang
2020-11-26  9:25 ` [PATCH V2 08/14] virtio-pci-modern: introduce helper for setting/geting queue size Jason Wang
2020-11-26  9:25 ` [PATCH V2 09/14] virtio-pci-modern: introduce helper for getting queue nums Jason Wang
2020-11-26  9:26 ` [PATCH V2 10/14] virtio-pci-modern: introduce helper to get notification offset Jason Wang
2020-11-26  9:26 ` [PATCH V2 11/14] virtio-pci: introduce modern device module Jason Wang
2020-11-26  9:26 ` [PATCH V2 12/14] vdpa: set the virtqueue num during register Jason Wang
2020-11-26  9:26 ` [PATCH V2 13/14] virtio_vdpa: don't warn when fail to disable vq Jason Wang
2020-11-26  9:26 ` [PATCH V2 14/14] vdpa: introduce virtio pci driver Jason Wang

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