linux-kernel - [PATCH v2 1/2] hyperv: Move hv_current_partition

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Message-Id: <1737596851-29555-2-git-send-email-nunodasneves@linux.microsoft.com>
Date: Wed, 22 Jan 2025 17:47:30 -0800
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: linux-hyperv@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org,
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Cc: kys@...rosoft.com,
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Subject: [PATCH v2 1/2] hyperv: Move hv_current_partition_id to arch-generic code

From: Nuno Das Neves <nudasnev@...rosoft.com>

Move hv_current_partition_id and hv_get_partition_id() to hv_common.c.
These aren't specific to x86_64 and will be needed by common code.

Set hv_current_partition_id to HV_PARTITION_ID_SELF by default.

Use a stack variable for the output of the hypercall. This allows moving
the call of hv_get_partition_id() to hv_common_init() before the percpu
pages are initialized.

Remove the BUG()s. Failing to get the id need not crash the machine.

Signed-off-by: Nuno Das Neves <nudasnev@...rosoft.com>
---
 arch/x86/hyperv/hv_init.c       | 26 --------------------------
 arch/x86/include/asm/mshyperv.h |  2 --
 drivers/hv/hv_common.c          | 23 +++++++++++++++++++++++
 include/asm-generic/mshyperv.h  |  1 +
 4 files changed, 24 insertions(+), 28 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 173005e6a95d..6b9f6f9f704d 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -34,9 +34,6 @@
 #include <clocksource/hyperv_timer.h>
 #include <linux/highmem.h>
 
-u64 hv_current_partition_id = ~0ull;
-EXPORT_SYMBOL_GPL(hv_current_partition_id);
-
 void *hv_hypercall_pg;
 EXPORT_SYMBOL_GPL(hv_hypercall_pg);
 
@@ -393,24 +390,6 @@ static void __init hv_stimer_setup_percpu_clockev(void)
 		old_setup_percpu_clockev();
 }
 
-static void __init hv_get_partition_id(void)
-{
-	struct hv_get_partition_id *output_page;
-	u64 status;
-	unsigned long flags;
-
-	local_irq_save(flags);
-	output_page = *this_cpu_ptr(hyperv_pcpu_output_arg);
-	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page);
-	if (!hv_result_success(status)) {
-		/* No point in proceeding if this failed */
-		pr_err("Failed to get partition ID: %lld\n", status);
-		BUG();
-	}
-	hv_current_partition_id = output_page->partition_id;
-	local_irq_restore(flags);
-}
-
 #if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
 static u8 __init get_vtl(void)
 {
@@ -605,11 +584,6 @@ void __init hyperv_init(void)
 
 	register_syscore_ops(&hv_syscore_ops);
 
-	if (cpuid_ebx(HYPERV_CPUID_FEATURES) & HV_ACCESS_PARTITION_ID)
-		hv_get_partition_id();
-
-	BUG_ON(hv_root_partition && hv_current_partition_id == ~0ull);
-
 #ifdef CONFIG_PCI_MSI
 	/*
 	 * If we're running as root, we want to create our own PCI MSI domain.
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index f91ab1e75f9f..8d3ada3e8d0d 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -43,8 +43,6 @@ extern bool hyperv_paravisor_present;
 
 extern void *hv_hypercall_pg;
 
-extern u64 hv_current_partition_id;
-
 extern union hv_ghcb * __percpu *hv_ghcb_pg;
 
 bool hv_isolation_type_snp(void);
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index af5d1dc451f6..1da19b64ef16 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -31,6 +31,9 @@
 #include <hyperv/hvhdk.h>
 #include <asm/mshyperv.h>
 
+u64 hv_current_partition_id = HV_PARTITION_ID_SELF;
+EXPORT_SYMBOL_GPL(hv_current_partition_id);
+
 /*
  * hv_root_partition, ms_hyperv and hv_nested are defined here with other
  * Hyper-V specific globals so they are shared across all architectures and are
@@ -283,6 +286,23 @@ static inline bool hv_output_page_exists(void)
 	return hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE);
 }
 
+static void __init hv_get_partition_id(void)
+{
+	/*
+	 * Note in this case the output can be on the stack because it is just
+	 * a single u64 and hence won't cross a page boundary.
+	 */
+	struct hv_get_partition_id output;
+	u64 status;
+
+	status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, &output);
+	if (!hv_result_success(status)) {
+		pr_err("Hyper-V: failed to get partition ID: %#lx\n", status);
+		return;
+	}
+	hv_current_partition_id = output.partition_id;
+}
+
 int __init hv_common_init(void)
 {
 	int i;
@@ -298,6 +318,9 @@ int __init hv_common_init(void)
 	if (hv_is_isolation_supported())
 		sysctl_record_panic_msg = 0;
 
+	if (ms_hyperv.priv_high & HV_ACCESS_PARTITION_ID)
+		hv_get_partition_id();
+
 	/*
 	 * Hyper-V expects to get crash register data or kmsg when
 	 * crash enlightment is available and system crashes. Set
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index a7bbe504e4f3..98100466e0b2 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -58,6 +58,7 @@ struct ms_hyperv_info {
 };
 extern struct ms_hyperv_info ms_hyperv;
 extern bool hv_nested;
+extern u64 hv_current_partition_id;
 
 extern void * __percpu *hyperv_pcpu_input_arg;
 extern void * __percpu *hyperv_pcpu_output_arg;
-- 
2.34.1