Re: [meta-virtualization] [PATCH 2/2] xen: Disable highmem on qemuarm

From: Bertrand Marquis <Bertrand.Marquis@arm.com>
To: Michal Orzel <Michal.Orzel@arm.com>
Cc: "christopher.w.clark@gmail.com" <christopher.w.clark@gmail.com>,
	"bruce.ashfield@gmail.com" <bruce.ashfield@gmail.com>,
	"meta-virtualization@lists.yoctoproject.org"
	<meta-virtualization@lists.yoctoproject.org>, nd <nd@arm.com>
Subject: Re: [meta-virtualization] [PATCH 2/2] xen: Disable highmem on qemuarm
Date: Thu, 9 Jun 2022 10:01:20 +0000	[thread overview]
Message-ID: <63C89F72-E463-4C2B-8026-B959173F5754@arm.com> (raw)
In-Reply-To: <20220609095748.176486-3-michal.orzel@arm.com>

Hi Michal,

> On 9 Jun 2022, at 10:57, Michal Orzel via lists.yoctoproject.org <michal.orzel=arm.com@lists.yoctoproject.org> wrote:
> 
> By default, highmem option is enabled for machine types later than
> virt-2.12. This allows qemu to place devices and RAM in physical
> address space above 32-bits. This can cause issues as according to the
> documentation Xen supports up to 12GiB of physical address space.
> Recently the issue was observed using runqemu, that was causing Linux
> running on top of Xen to stall when trying to access ECAM space placed
> by qemu at 256GiB mark. Even though this issue is most probably related
> to QEMU and not Xen (the investigation showed that it can map ECAM
> space correctly), it is best to avoid such issues by disabling highmem
> on qemuarm.
> 
> Signed-off-by: Michal Orzel <michal.orzel@arm.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

Also tested on kirkstone and dom0 boots fine and pci is working.

Thanks a lot
Cheers
Bertrand

> ---
> classes/qemuboot-xen-defaults.bbclass | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/classes/qemuboot-xen-defaults.bbclass b/classes/qemuboot-xen-defaults.bbclass
> index f1550cc..460cbe6 100644
> --- a/classes/qemuboot-xen-defaults.bbclass
> +++ b/classes/qemuboot-xen-defaults.bbclass
> @@ -23,8 +23,10 @@ QB_DEFAULT_KERNEL:qemuarm = "xen-${MACHINE}"
> 
> # 64-bit Arm: gic version 3
> QB_MACHINE:qemuarm64 = "-machine virt,gic-version=3 -machine virtualization=true"
> -# 32-bit Arm
> -QB_MACHINE:qemuarm = "-machine virt -machine virtualization=true"
> +# 32-bit Arm: highmem=off
> +# Disable highmem so that qemu does not use highmem IO regions that end up
> +# being placed at the 256GiB mark (e.g. ECAM space) and can cause issues in Xen.
> +QB_MACHINE:qemuarm = "-machine virt,highmem=off -machine virtualization=true"
> 
> # Increase the default qemu memory allocation to allow for the hypervisor.
> # Use a weak assignment to allow for change of default and override elsewhere.
> -- 
> 2.25.1
> 
> 
> -=-=-=-=-=-=-=-=-=-=-=-
> Links: You receive all messages sent to this group.
> View/Reply Online (#7352): https://lists.yoctoproject.org/g/meta-virtualization/message/7352
> Mute This Topic: https://lists.yoctoproject.org/mt/91642064/3619089
> Group Owner: meta-virtualization+owner@lists.yoctoproject.org
> Unsubscribe: https://lists.yoctoproject.org/g/meta-virtualization/unsub [bertrand.marquis@arm.com]
> -=-=-=-=-=-=-=-=-=-=-=-
> 