Subject: Re: [PATCH V4 0/6] xen: Add support of extended regions (safe ranges)
 on Arm
From:   Oleksandr <olekstysh@gmail.com>
To:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>
Cc:     xen-devel@lists.xenproject.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Julien Grall <julien@xen.org>,
        Bertrand Marquis <bertrand.marquis@arm.com>,
        Wei Chen <Wei.Chen@arm.com>, Henry Wang <Henry.Wang@arm.com>,
        Kaly Xin <Kaly.Xin@arm.com>, Jiamei Xie <Jiamei.Xie@arm.com>
References: <1639080336-26573-1-git-send-email-olekstysh@gmail.com>
Message-ID: <1428a0be-b80c-f996-1f72-6545dd66c1bf@gmail.com>
Date:   Fri, 17 Dec 2021 00:02:52 +0200
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On 09.12.21 22:05, Oleksandr Tyshchenko wrote:


Hello Juergen, Boris


May I please ask, are you happy (or otherwise) with current patch series 
(I assume, especially with commits #3-4)?

For the convenience:

   1. xen/unpopulated-alloc: Drop check for virt_addr_valid() in fill_list()
- Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

   2. arm/xen: Switch to use gnttab_setup_auto_xlat_frames() for DT
- Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

   3. xen/balloon: Bring alloc(free)_xenballooned_pages helpers back
- Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

   4. xen/unpopulated-alloc: Add mechanism to use Xen resource
- Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

   5. arm/xen: Read extended regions from DT and init Xen resource
- Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

   6. dt-bindings: xen: Clarify "reg" purpose
- Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
- Acked-by: Rob Herring <robh@kernel.org>
- Acked-by: Stefano Stabellini <sstabellini@kernel.org>


> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>
> 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@gmail.com/
>      https://lore.kernel.org/all/1627490656-1267-2-git-send-email-olekstysh@gmail.com/
> [2] https://lore.kernel.org/all/1635264312-3796-1-git-send-email-olekstysh@gmail.com/
> [3] https://lore.kernel.org/all/1637787223-21129-1-git-send-email-olekstysh@gmail.com/
> [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(-)
>
-- 
Regards,

Oleksandr Tyshchenko