Received-SPF: pass (google.com: domain of linux-kernel+bounces-179921-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45d1:ec00::1 as permitted sender) client-ip=2604:1380:45d1:ec00::1;
From: Michael Kelley <mhklinux@outlook.com>
To: Roman Kisel <romank@linux.microsoft.com>, "arnd@arndb.de" <arnd@arndb.de>,
	"bhelgaas@google.com" <bhelgaas@google.com>, "bp@alien8.de" <bp@alien8.de>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"decui@microsoft.com" <decui@microsoft.com>, "haiyangz@microsoft.com"
	<haiyangz@microsoft.com>, "hpa@zytor.com" <hpa@zytor.com>, "kw@linux.com"
	<kw@linux.com>, "kys@microsoft.com" <kys@microsoft.com>, "lenb@kernel.org"
	<lenb@kernel.org>, "lpieralisi@kernel.org" <lpieralisi@kernel.org>,
	"mingo@redhat.com" <mingo@redhat.com>, "rafael@kernel.org"
	<rafael@kernel.org>, "robh@kernel.org" <robh@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>, "wei.liu@kernel.org"
	<wei.liu@kernel.org>, "will@kernel.org" <will@kernel.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>, "linux-hyperv@vger.kernel.org"
	<linux-hyperv@vger.kernel.org>, "linux-kernel@vger.kernel.org"
	<linux-kernel@vger.kernel.org>, "linux-pci@vger.kernel.org"
	<linux-pci@vger.kernel.org>, "x86@kernel.org" <x86@kernel.org>
CC: "ssengar@microsoft.com" <ssengar@microsoft.com>, "sunilmut@microsoft.com"
	<sunilmut@microsoft.com>, "vdso@hexbites.dev" <vdso@hexbites.dev>
Subject: RE: [PATCH v2 2/6] drivers/hv: Enable VTL mode for arm64
Thread-Topic: [PATCH v2 2/6] drivers/hv: Enable VTL mode for arm64
Thread-Index: AQHaplCGevGI4HwmaE+AFdHRKNc30LGXiWwA
Date: Wed, 15 May 2024 13:37:06 +0000
Message-ID:
 <SN6PR02MB4157E15EFE263BBA3D8DFC51D4EC2@SN6PR02MB4157.namprd02.prod.outlook.com>
References: <20240514224508.212318-1-romank@linux.microsoft.com>
 <20240514224508.212318-3-romank@linux.microsoft.com>
In-Reply-To: <20240514224508.212318-3-romank@linux.microsoft.com>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0:
 =?us-ascii?Q?bTJl3bhDyt7Em3DZCHcY4lKv5wZO1eIiYQD2lgw85grlwesydApTfgLhdCNe?=
 =?us-ascii?Q?w8bSNZDa11wUqJIUrRW6SDBmGAMRteH8dWJ2u6Fp+yHkB5djSgHXWHLAUdWN?=
 =?us-ascii?Q?FTHIf5YBfOiXnjxY2mWRqaP7bBMqmgsaoBXGLDHh4GnJPtZ/Y+4flCjHIU1/?=
 =?us-ascii?Q?6vipyT899Rk09jsAhh/5f60IslqkG4WV7fInFMfj2eU5fjLrznsm9L9I8UWg?=
 =?us-ascii?Q?jh/Hasp6JKKyGIU6laJYhOb5PQG9B4u2wXyG5fCj0F/ca0WjN3lUzQLwdb5d?=
 =?us-ascii?Q?VbXX8I1c/CKeBkGFKtuNSNYiX7x+i7BRkbXLyGpL1X+2CKEydVtRib6CtGtZ?=
 =?us-ascii?Q?PHQvFhrrfAXeWV6MhoJpWX+dbSimrPa/wyz6rgd2M15AaueAyV7MXVzk7cJw?=
 =?us-ascii?Q?vqezPLPZauOAYdUHpmO/Wm6qXEkZxUO4sh/g46NL/fDMY7EiyQM65rP0b7SJ?=
 =?us-ascii?Q?Bq0m4jjE6IlFB9Dk64X25rLNPSCiyXaDBLYTxGHX1kAGXRrfSEgHbAN9sLpp?=
 =?us-ascii?Q?/vdtyH0jLBPkCS3My7mwzaQK6cwBxR7MC4rIpZN669o5402sd1Zt5x7yHEks?=
 =?us-ascii?Q?Gd+MC0zqtIe6154MuTvZ+cX3kTBHswjlgrHahM6cCFVZPF3/zIJ6NTeJ577A?=
 =?us-ascii?Q?XArq37uL9p8BNdkJuLZzf4OmI/AZbMWcQkm5WynlHDvqxi9oL/S2vOTG9HoR?=
 =?us-ascii?Q?NQV+0+vN21TKrKJsRYkOFIdgr8V4NGwggjdgNmdJ0c/avdCxylWKs19RJCq8?=
 =?us-ascii?Q?VTwj6NmRVPh8kspSspATivCNkBW4pa/NSPSoRwOkfGAGHrH29hkBurf2ojNy?=
 =?us-ascii?Q?P7Xyfb9Lh3Y8SCwSsTF6AD/euCjuG7+YPdIpnsCiWaP2idfkxbCgPluRaPmL?=
 =?us-ascii?Q?s/0EubP0I19ZSLFVFRMERz+kvT41r1/MEcQRiE3BrrSatt6jJ0b05CE99TUu?=
 =?us-ascii?Q?vQfhyUkGxwFuhB/dvjsW//otBo567io6Vf3Tq7eNaRx57ltoy9auixPSweQI?=
 =?us-ascii?Q?aymrsT8JMT/nBpUM5TJG1fw1H+7s7lJfXq/RKIwXtFXA6dsu+ZvjsjXCDMJi?=
 =?us-ascii?Q?Oew4DWAyt52soZXaI3qpoKpfO9jGE+NPWFDHdZcwjv334mmHM0/f0KIocUcl?=
 =?us-ascii?Q?UiMAkJSfO32HizGhvdM07QVks6/cj0Eg2Qfu5UQ7bP49tn4d2zcQou3BKBi2?=
 =?us-ascii?Q?nc0bHuq8d6TQY2QscI9Lx/0zBcc3F8mMVInRPeA24VBtcoNj0TJ50DGSDjE?=
 =?us-ascii?Q?=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
X-OriginatorOrg: outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: SN6PR02MB4157.namprd02.prod.outlook.com
X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-Network-Message-Id: 2bd80f70-9858-4a99-548b-08dc74e41d28
X-MS-Exchange-CrossTenant-rms-persistedconsumerorg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-originalarrivaltime: 15 May 2024 13:37:06.9820
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR02MB9491

From: Roman Kisel <romank@linux.microsoft.com> Sent: Tuesday, May 14, 2024 =
3:44 PM
>=20
> Kconfig dependencies for arm64 guests on Hyper-V require that be ACPI ena=
bled,
> and limit VTL mode to x86/x64. To enable VTL mode on arm64 as well, updat=
e the
> dependencies. Since VTL mode requires DeviceTree instead of ACPI, don't r=
equire
> arm64 guests on Hyper-V to have ACPI.
>=20
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
>  drivers/hv/Kconfig | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>=20
> diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
> index 862c47b191af..a5cd1365e248 100644
> --- a/drivers/hv/Kconfig
> +++ b/drivers/hv/Kconfig
> @@ -5,7 +5,7 @@ menu "Microsoft Hyper-V guest support"
>  config HYPERV
>  	tristate "Microsoft Hyper-V client drivers"
>  	depends on (X86 && X86_LOCAL_APIC && HYPERVISOR_GUEST) \
> -		|| (ACPI && ARM64 && !CPU_BIG_ENDIAN)
> +		|| (ARM64 && !CPU_BIG_ENDIAN)
>  	select PARAVIRT
>  	select X86_HV_CALLBACK_VECTOR if X86
>  	select OF_EARLY_FLATTREE if OF
> @@ -15,7 +15,7 @@ config HYPERV
>=20
>  config HYPERV_VTL_MODE
>  	bool "Enable Linux to boot in VTL context"
> -	depends on X86_64 && HYPERV
> +	depends on HYPERV
>  	depends on SMP
>  	default n
>  	help

These changes make it possible to build a normal VTL 0 Hyper-V
guest (i.e., CONFIG_HYPERV_VTL_MODE=3Dn) if CONFIG_ACPI is
not set, which won't work.  While we can say "don't do that", it
would be better if the Kconfig dependencies expressed that
requirement.

A possible fix is to remove the "depends on HYPERV" from
HYPERV_VTL_MODE.  Then for HYPERV, make
the "depends on ACPI" be conditional on !HYPERV_VTL_MODE
(for both ARM64 and X86).

I think we originally had "depends on HYPERV" in
HYPERV_VTL_MODE because there was a VTL-related function
in a non-Hyper-V code path, and we wanted to prevent that code
from running in non-Hyper-V environments.  But in practice, that
turned out not to work well because occasionally people would
do an "all config" build where both CONFIG_HYPERV and
CONFIG_HYPERV_VTL_MODE were set, and it would panic during
boot in their non-Hyper-V environment.  Such people were not
happy. :-(  So Saurabh made a relatively simple change (see commit
14058f72cf13e) that got the VTL code out of that non-Hyper-V code
path.  With that change, it shouldn't matter if someone sets
CONFIG_HYPERV_VTL_MODE=3Dy in a build where
CONFIG_HYPERV=3Dn.

At least that's my theory. :-)  Someone would need to check
it carefully.

Michael