Subject: Re: [PATCH V4 0/6] xen: Add support of extended regions (safe ranges)
 on Arm
To:     Oleksandr Tyshchenko <olekstysh@gmail.com>,
        xen-devel@lists.xenproject.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        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>
From:   Juergen Gross <jgross@suse.com>
Message-ID: <d594a183-c7be-5fff-da7a-e4c1e707b83c@suse.com>
Date:   Fri, 7 Jan 2022 12:31:30 +0100
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From: Juergen Gross <jgross@suse.com>
To: Oleksandr Tyshchenko <olekstysh@gmail.com>,
 xen-devel@lists.xenproject.org, linux-arm-kernel@lists.infradead.org,
 linux-kernel@vger.kernel.org
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
 Stefano Stabellini <sstabellini@kernel.org>,
 Russell King <linux@armlinux.org.uk>,
 Boris Ostrovsky <boris.ostrovsky@oracle.com>, 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>
Message-ID: <d594a183-c7be-5fff-da7a-e4c1e707b83c@suse.com>
Subject: Re: [PATCH V4 0/6] xen: Add support of extended regions (safe ranges)
 on Arm
References: <1639080336-26573-1-git-send-email-olekstysh@gmail.com>
In-Reply-To: <1639080336-26573-1-git-send-email-olekstysh@gmail.com>

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On 09.12.21 21:05, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>=20
> Hello all.
>=20
> You can find the RFC-V3 patch series at [1],[2] and [3].
>=20
> The corresponding Xen support (for both Dom0 and DomU) is already commi=
tted and
> is available in mainline Xen since the following commit:
> 57f87857dc2de452a796d6bad4f476510efd2aba libxl/arm: Add handling of ext=
ended regions for DomU
>=20
> 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 mappin=
gs 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 shatt=
ering super
> pages in P2M table).
>=20
> The problem is that we cannot follow Linux advise which memory ranges a=
re 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 t=
he 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 region=
s (which won't
> clash with other resources).
>=20
> The extended regions are chosen at the domain creation time and adverti=
sed to it via
> "reg" property under hypervisor node in the guest device-tree [4]. As r=
egion 0 is reserved
> for grant table space (always present), the indexes for extended region=
s 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.
>=20
> 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
>=20
> The patch series is based on v5.16-rc3 and also available at [5], it wa=
s fully
> tested on Arm64 and only compile tested on x86.
>=20
> [1] https://lore.kernel.org/all/1627490656-1267-1-git-send-email-olekst=
ysh@gmail.com/
>      https://lore.kernel.org/all/1627490656-1267-2-git-send-email-oleks=
tysh@gmail.com/
> [2] https://lore.kernel.org/all/1635264312-3796-1-git-send-email-olekst=
ysh@gmail.com/
> [3] https://lore.kernel.org/all/1637787223-21129-1-git-send-email-oleks=
tysh@gmail.com/
> [4] https://xenbits.xen.org/gitweb/?p=3Dxen.git;a=3Dblob_plain;f=3Ddocs=
/misc/arm/device-tree/guest.txt;hb=3Drefs/heads/master
> [5] https://github.com/otyshchenko1/linux/commits/map_opt_ml7
>=20
> 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
>=20
>   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(-)
>=20

Series pushed to xen/tip.git for-linus-5.17


Juergen

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