Re: [PATCH v5 07/16] x86/hyperv: extract partition ID from Microsoft Hypervisor if necessary

On Tue, Jan 26, 2021 at 12:48:37AM +0000, Michael Kelley wrote:

From: Wei Liu <wei.liu@kernel.org> Sent: Wednesday, January 20, 2021 4:01 AM

quoted

We will need the partition ID for executing some hypercalls later.

Signed-off-by: Lillian Grassin-Drake <redacted>
Co-Developed-by: Sunil Muthuswamy <redacted>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
---
v3:
1. Make hv_get_partition_id static.
2. Change code structure a bit.
---
 arch/x86/hyperv/hv_init.c         | 27 +++++++++++++++++++++++++++
 arch/x86/include/asm/mshyperv.h   |  2 ++
 include/asm-generic/hyperv-tlfs.h |  6 ++++++
 3 files changed, 35 insertions(+)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 6f4cb40e53fe..fc9941bd8653 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c

@@ -26,6 +26,9 @@
 #include <linux/syscore_ops.h>
 #include <clocksource/hyperv_timer.h>

+u64 hv_current_partition_id = ~0ull;
+EXPORT_SYMBOL_GPL(hv_current_partition_id);
+
 void *hv_hypercall_pg;
 EXPORT_SYMBOL_GPL(hv_hypercall_pg);

@@ -331,6 +334,25 @@ static struct syscore_ops hv_syscore_ops = {
 	.resume		= hv_resume,
 };

+static void __init hv_get_partition_id(void)
+{
+	struct hv_get_partition_id *output_page;
+	u16 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) &
+		HV_HYPERCALL_RESULT_MASK;
+	if (status != HV_STATUS_SUCCESS) {

Across the Hyper-V code in Linux, the way we check the hypercall result
is very inconsistent.  IMHO, the and'ing of hv_do_hypercall() with 
HV_HYPERCALL_RESULT_MASK so that status can be a u16 is stylistically
a bit unusual.

I'd like to see the hypercall result being stored into a u64 local variable.
Then the subsequent test for the status should 'and' the u64 with
HV_HYPERCALL_RESULT_MASK to determine the result code.
I've made a note to go fix the places that aren't doing it that way.

I will fold in the following diff in the next version. I will also check
if there are other instances in this patch series that need fixing.
Pretty sure there are a few.

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index fc9941bd8653..6064f64a1295 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c

@@ -337,14 +337,13 @@ static struct syscore_ops hv_syscore_ops = {
 static void __init hv_get_partition_id(void)
 {
        struct hv_get_partition_id *output_page;
-       u16 status;
+       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) &
-               HV_HYPERCALL_RESULT_MASK;
-       if (status != HV_STATUS_SUCCESS) {
+       status = hv_do_hypercall(HVCALL_GET_PARTITION_ID, NULL, output_page);
+       if ((status & HV_HYPERCALL_RESULT_MASK) != HV_STATUS_SUCCESS) {
                /* No point in proceeding if this failed */
                pr_err("Failed to get partition ID: %d\n", status);
                BUG();

quoted

+		/* No point in proceeding if this failed */
+		pr_err("Failed to get partition ID: %d\n", status);
+		BUG();
+	}
+	hv_current_partition_id = output_page->partition_id;
+	local_irq_restore(flags);
+}
+
 /*
  * This function is to be invoked early in the boot sequence after the
  * hypervisor has been detected.

@@ -426,6 +448,11 @@ 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();

Another place where the EBX value saved into the ms_hyperv structure
could be used.

If you're okay with my response earlier, this will be handled later in
another patch (series).

Wei.