Re: [PATCH V4 0/6] xen: Add support of extended regions (safe ranges) on Arm

[Juergen Gross <jgross@xxxxxxxx>]

On 09.12.21 21:05, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>
> Hello all.
>
> You can find the RFC-V3 patch series at [1],[2] and [3].
>
> The corresponding Xen support (for both Dom0 and DomU) is already committed and
> is available in mainline Xen since the following commit:
> 57f87857dc2de452a796d6bad4f476510efd2aba libxl/arm: Add handling of extended 
> regions for DomU
>
> The extended region (safe range) is a region of guest physical address space
> which is unused and could be safely used to create grant/foreign mappings 
> instead
> of ballooning out real RAM pages to obtain a physical address space for creating
> these mappings (which simply results in wasting domain memory and shattering 
> super
> pages in P2M table).
>
> The problem is that we cannot follow Linux advise which memory ranges are unused
> on Arm as there might be some identity mappings in P2M table (stage 2) the 
> guest is not
> aware of or not all device I/O regions might be known (registered) by the time 
> the guest
> starts creating grant/foreign mappings. This is why we need some hints from the 
> hypervisor
> which knows all details in advance to be able to choose extended regions (which 
> won't
> clash with other resources).
>
> The extended regions are chosen at the domain creation time and advertised to 
> it via
> "reg" property under hypervisor node in the guest device-tree [4]. As region 0 
> is reserved
> for grant table space (always present), the indexes for extended regions are 
> 1...N.
> No device tree bindings update is needed, guest infers the presence of extended 
> regions
> from the number of regions in "reg" property.
>
> Please note the following:
> - The ACPI case is not covered for now
> - patch series was created in a way to retain existing behavior on x86
>
> The patch series is based on v5.16-rc3 and also available at [5], it was fully
> tested on Arm64 and only compile tested on x86.
>
> [1] 
> https://lore.kernel.org/all/1627490656-1267-1-git-send-email-olekstysh@xxxxxxxxx/
>      
> https://lore.kernel.org/all/1627490656-1267-2-git-send-email-olekstysh@xxxxxxxxx/
> [2] 
> https://lore.kernel.org/all/1635264312-3796-1-git-send-email-olekstysh@xxxxxxxxx/
> [3] 
> https://lore.kernel.org/all/1637787223-21129-1-git-send-email-olekstysh@xxxxxxxxx/
> [4] 
> https://xenbits.xen.org/gitweb/?p=xen.git;a=blob_plain;f=docs/misc/arm/device-tree/guest.txt;hb=refs/heads/master
> [5] https://github.com/otyshchenko1/linux/commits/map_opt_ml7
>
> Oleksandr Tyshchenko (6):
>    xen/unpopulated-alloc: Drop check for virt_addr_valid() in fill_list()
>    arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT
>    xen/balloon: Bring alloc(free)_xenballooned_pages helpers back
>    xen/unpopulated-alloc: Add mechanism to use Xen resource
>    arm/xen: Read extended regions from DT and init Xen resource
>    dt-bindings: xen: Clarify "reg" purpose
>
>   Documentation/devicetree/bindings/arm/xen.txt |  14 +--
>   arch/arm/xen/enlighten.c                      | 132 ++++++++++++++++++++++++--
>   drivers/xen/Kconfig                           |   2 +-
>   drivers/xen/balloon.c                         |  20 ++--
>   drivers/xen/unpopulated-alloc.c               |  87 ++++++++++++++++-
>   include/xen/balloon.h                         |   3 +
>   include/xen/xen.h                             |  16 ++++
>   7 files changed, 245 insertions(+), 29 deletions(-)
Series pushed to xen/tip.git for-linus-5.17


Juergen

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