Re: [PATCH v2 4/6] arm64/hyperv: Boot in a Virtual Trust Level

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On 5/15/2024 6:39 AM, Michael Kelley wrote:
From: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx> Sent: Tuesday, May 14, 2024 3:44 PM

To run in the VTL mode, Hyper-V drivers have to know what
VTL the system boots in, and the arm64/hyperv code does not
update the variable that stores the value.

Update the variable to enable the Hyper-V drivers to boot
in the VTL mode and print the VTL the code runs in.

Signed-off-by: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx>
  arch/arm64/hyperv/Makefile        |  1 +
  arch/arm64/hyperv/hv_vtl.c        | 19 +++++++++++++++++++
  arch/arm64/hyperv/mshyperv.c      |  6 ++++++
  arch/arm64/include/asm/mshyperv.h |  8 ++++++++
  arch/x86/hyperv/hv_vtl.c          |  2 +-
  5 files changed, 35 insertions(+), 1 deletion(-)
  create mode 100644 arch/arm64/hyperv/hv_vtl.c

diff --git a/arch/arm64/hyperv/Makefile b/arch/arm64/hyperv/Makefile
index 87c31c001da9..9701a837a6e1 100644
--- a/arch/arm64/hyperv/Makefile
+++ b/arch/arm64/hyperv/Makefile
@@ -1,2 +1,3 @@
  # SPDX-License-Identifier: GPL-2.0
  obj-y		:= hv_core.o mshyperv.o
+obj-$(CONFIG_HYPERV_VTL_MODE)	+= hv_vtl.o
diff --git a/arch/arm64/hyperv/hv_vtl.c b/arch/arm64/hyperv/hv_vtl.c
new file mode 100644
index 000000000000..9b44cc49594c
--- /dev/null
+++ b/arch/arm64/hyperv/hv_vtl.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+ * Copyright (C) 2023, Microsoft, Inc.
+ *
+ * Author : Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx>
+ */
+#include <asm/mshyperv.h>
+void __init hv_vtl_init_platform(void)
+	pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);
+int __init hv_vtl_early_init(void)
+	return 0;
diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 208a3bcb9686..cbde483b167a 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -96,6 +96,12 @@ static int __init hyperv_init(void)
  		return ret;

+	/* Find the VTL */
+	ms_hyperv.vtl = get_vtl();
+	if (ms_hyperv.vtl > 0) /* non default VTL */
+		hv_vtl_early_init();

Since hv_vtl_early_init() doesn't do anything on arm64, is the above
and the empty implementation of hv_vtl_early_init() really needed?
I thought maybe a subsequent patch in this series would populate
hv_vtl_early_init() to do something, but I didn't see such.  I realize
the functions hv_vtl_init_platform() and hv_vtl_early_init() parallel
equivalent functions on x86, but I'd say drop hv_vtl_early_init() on
arm64 if it isn't needed.

Note too that the naming on the x86 side is arguably a bit messed
up. hv_vtl_init_platform() runs *before* hv_vtl_early_init().  But
typically in the Linux kernel, functions with "early init" in the name
run very early in boot, and that's not the case here.  hv_vtl_init_platform()
is actually the function that runs very early in boot, but its name is
set up to parallel ms_hyperv_init_platform(), which calls it.  On the
x86 side, I'd would argue for renaming hv_vtl_init_platform() to
hv_vtl_early_init(), and then hv_vtl_early_init() becomes hv_vtl_init().
But that's probably a separate patch.  Here on arm64, perhaps all
you need is hv_vtl_init().

I'll clean that up, appreciate the thorough explanation!


+	hv_vtl_init_platform();

  	hyperv_initialized = true;
diff --git a/arch/arm64/include/asm/mshyperv.h
index a975e1a689dd..4a8ff6be389c 100644
--- a/arch/arm64/include/asm/mshyperv.h
+++ b/arch/arm64/include/asm/mshyperv.h
@@ -49,6 +49,14 @@ static inline u64 hv_get_msr(unsigned int reg)

+void __init hv_vtl_init_platform(void);
+int __init hv_vtl_early_init(void);
+static inline void __init hv_vtl_init_platform(void) {}
+static inline int __init hv_vtl_early_init(void) { return 0; }
  #include <asm-generic/mshyperv.h>

diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 92bd5a55f093..ae3105375a12 100644
--- a/arch/x86/hyperv/hv_vtl.c
+++ b/arch/x86/hyperv/hv_vtl.c
@@ -19,7 +19,7 @@ static struct real_mode_header hv_vtl_real_mode_header;

  void __init hv_vtl_init_platform(void)
-	pr_info("Linux runs in Hyper-V Virtual Trust Level\n");
+	pr_info("Linux runs in Hyper-V Virtual Trust Level %d\n", ms_hyperv.vtl);

  	x86_platform.realmode_reserve = x86_init_noop;
  	x86_platform.realmode_init = x86_init_noop;

Thank you,

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