On Sat, 14 Mar 2020 08:35:12 -0700 Michael Kelley wrote:

+/*
+ * Get the value of a single VP register.  One version
+ * returns just 64 bits and another returns the full 128 bits.
+ * The two versions are separate to avoid complicating the
+ * calling sequence for the more frequently used 64 bit version.
+ */
+
+/*
+ * Input and output memory allocation sizes are rounded up to a power
+ * of 2 so kmalloc() will guarantee alignment. In turn, the alignment
+ * ensures that the allocations don't cross a page boundary, which is

Better to specify kmalloc's current alignment and why it fails to ensure
(4 * sizeof(u64))-sized allocations wont cross page boundary.

+ * required by the hypercall interface.
+ */
+#define INPUTSIZE (4 * sizeof(u64))
+#define OUTPUTSIZE (2 * sizeof(u64))
+
+static void __hv_get_vpreg_128(u32 msr, struct hv_get_vp_register_output *res)
+{
+	union hv_hypercall_status		status;
+	struct hv_get_vp_register_input		*input;
+
+	BUILD_BUG_ON(sizeof(*input) > INPUTSIZE);
+
+	input = kzalloc(INPUTSIZE, GFP_ATOMIC);
+
+	input->partitionid = HV_PARTITION_ID_SELF;
+	input->vpindex = HV_VP_INDEX_SELF;
+	input->inputvtl = 0;
+	input->name0 = msr;
+	input->name1 = 0;
+
+
+	status.as_uint64 = hv_do_hypercall(
+		HVCALL_GET_VP_REGISTERS | HV_HYPERCALL_REP_COUNT_1,
+		input, res);
+
+	/*
+	 * Something is fundamentally broken in the hypervisor if
+	 * getting a VP register fails. There's really no way to
+	 * continue as a guest VM, so panic.
+	 */
+	BUG_ON(status.status != HV_STATUS_SUCCESS);
+
+	kfree(input);
+}

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