linux-kernel - [PATCH hyperv-next 0/2] x86/hyperv: VTL mode reboot fixes

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Message-Id: <20250117210702.1529580-1-romank@linux.microsoft.com>
Date: Fri, 17 Jan 2025 13:07:00 -0800
From: Roman Kisel <romank@...ux.microsoft.com>
To: bp@...en8.de,
	dave.hansen@...ux.intel.com,
	decui@...rosoft.com,
	haiyangz@...rosoft.com,
	hpa@...or.com,
	kys@...rosoft.com,
	mingo@...hat.com,
	ssengar@...ux.microsoft.com,
	tglx@...utronix.de,
	wei.liu@...nel.org,
	linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc: apais@...rosoft.com,
	benhill@...rosoft.com,
	sunilmut@...rosoft.com,
	vdso@...bites.dev
Subject: [PATCH hyperv-next 0/2] x86/hyperv: VTL mode reboot fixes

The first patch defines a specialized machine emergency restart
callback not to write to the physical address of 0x472 which is
what the native_machine_emergency_restart() does unconditionally.

I first wanted to tweak that function[1], and in the course of
the discussion it looked as the risks of doing that would
outweigh the benefit: the bare-metal systems have likely adopted
that behavior as a standard although I could not find any mentions
of that magic address in the UEFI+ACPI specification.

The second patch removes the need to always supply "reboot=t"
to the kernel command line in the OpenHCL bootloader [2]. There is
no other option at the moment; when/if it appears the newly added
callback's code can be adjusted as required.

It would be great to apply this to the stable tree if no concerns,
should apply cleanly.

[1] https://lore.kernel.org/all/20250109204352.1720337-1-romank@linux.microsoft.com/
[2] https://github.com/microsoft/openvmm/blob/7a9d0e0a00461be6e5f3267af9ea54cc7157c900/openhcl/openhcl_boot/src/main.rs#L139

Roman Kisel (2):
  x86/hyperv: VTL mode emergency restart callback
  x86/hyperv: VTL mode callback for restarting the system

 arch/x86/hyperv/hv_vtl.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

base-commit: 2e03358be78b65d28b66e17aca9e0c8700b0df78
-- 
2.34.1