linux-kernel - Re: [PATCH v18 06/10] virtio_ring: add a new API, virtqueue_add_one

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Message-ID: <5A210D6D.3090402@intel.com>
Date:   Fri, 01 Dec 2017 16:06:05 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mhocko@...nel.org,
        akpm@...ux-foundation.org, mawilcox@...rosoft.com,
        david@...hat.com, penguin-kernel@...ove.SAKURA.ne.jp,
        cornelia.huck@...ibm.com, mgorman@...hsingularity.net,
        aarcange@...hat.com, amit.shah@...hat.com, pbonzini@...hat.com,
        willy@...radead.org, liliang.opensource@...il.com,
        yang.zhang.wz@...il.com, quan.xu@...yun.com, nilal@...hat.com,
        riel@...hat.com
Subject: Re: [PATCH v18 06/10] virtio_ring: add a new API, virtqueue_add_one_desc

On 12/01/2017 03:38 AM, Michael S. Tsirkin wrote:
> On Wed, Nov 29, 2017 at 09:55:22PM +0800, Wei Wang wrote:
>> Current virtqueue_add API implementation is based on the scatterlist
>> struct, which uses kaddr. This is inadequate to all the use case of
>> vring. For example:
>> - Some usages don't use IOMMU, in this case the user can directly pass
>>    in a physical address in hand, instead of going through the sg
>>    implementation (e.g. the VIRTIO_BALLOON_F_SG feature)
>> - Sometimes, a guest physical page may not have a kaddr (e.g. high
>>    memory) but need to use vring (e.g. the VIRTIO_BALLOON_F_FREE_PAGE_VQ
>>    feature)
>>
>> The new API virtqueue_add_one_desc enables the caller to assign a vring
>> desc with a physical address and len. Also, factor out the common code
>> with virtqueue_add in vring_set_avail.
>>
>> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
>> Cc: Michael S. Tsirkin <mst@...hat.com>
> You previously managed without this patch, and it's preferable
> IMHO since this patchset is already too big.
>
> I don't really understand what is wrong with virtio_add_sgs + sg_set_page.
> I don't think is assumes a kaddr.
>

OK, I will use the previous method to send sgs.
Please have a check if there are other things need to be improved.

Best,
Wei