Re: [PATCH v3 00/10] direct-map memory map

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 16 Nov 2021, Penny Zheng wrote:
> Cases where domU needs direct-map memory map:
>   * IOMMU not present in the system.
>   * IOMMU disabled if it doesn't cover a specific device and all the guests
> are trusted. Thinking a mixed scenario, where a few devices with IOMMU and
> a few without, then guest DMA security still could not be totally guaranteed.
> So users may want to disable the IOMMU, to at least gain some performance
> improvement from IOMMU disabled.
>   * IOMMU disabled as a workaround when it doesn't have enough bandwidth.
> To be specific, in a few extreme situation, when multiple devices do DMA
> concurrently, these requests may exceed IOMMU's transmission capacity.
>   * IOMMU disabled when it adds too much latency on DMA. For example,
> TLB may be missing in some IOMMU hardware, which may bring latency in DMA
> progress, so users may want to disable it in some realtime scenario.
>   * Guest OS relies on the host memory layout
> 
> "direct-map" property shall be added under the appropriate domain node,
> when users requesting direct-map memory mapping for the domain.
> 
> Right now, direct-map is only supported when domain on Static Allocation,
> that is, "xen,static-mem" is also necessary in the domain configuration.
> 
> Looking into related [design link](
> https://lists.xenproject.org/archives/html/xen-devel/2021-05/msg00882.html)
> for more details.
> 
> The whole design is about Static Allocation and direct-map, and this
> Patch Serie only covers parts of it, which are direct-map memory map.
> Other features will be delievered through different patch series.
> 
> See https://lists.xenproject.org/archives/html/xen-devel/2021-09/msg00855.html
> for Domain on Static Allocation.
> 
> This patch serie is based on
> https://lists.xenproject.org/archives/html/xen-devel/2021-10/msg00822.html

I haven't had a chance to review the series but I wanted to say that I
tested it successfully both with and without direct-map, so:

Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>