1// SPDX-License-Identifier: GPL-2.0
 2
 3/*
 4 * Architecture neutral utility routines for interacting with
 5 * Hyper-V. This file is specifically for code that must be
 6 * built-in to the kernel image when CONFIG_HYPERV is set
 7 * (vs. being in a module) because it is called from architecture
 8 * specific code under arch/.
 9 *
10 * Copyright (C) 2021, Microsoft, Inc.
11 *
12 * Author : Michael Kelley <mikelley@microsoft.com>
13 */
14
15#include <linux/types.h>
16#include <linux/export.h>
17#include <linux/bitfield.h>
18#include <asm/hyperv-tlfs.h>
19#include <asm/mshyperv.h>
20
21
22/* Bit mask of the extended capability to query: see HV_EXT_CAPABILITY_xxx */
23bool hv_query_ext_cap(u64 cap_query)
24{
25	/*
26	 * The address of the 'hv_extended_cap' variable will be used as an
27	 * output parameter to the hypercall below and so it should be
28	 * compatible with 'virt_to_phys'. Which means, it's address should be
29	 * directly mapped. Use 'static' to keep it compatible; stack variables
30	 * can be virtually mapped, making them incompatible with
31	 * 'virt_to_phys'.
32	 * Hypercall input/output addresses should also be 8-byte aligned.
33	 */
34	static u64 hv_extended_cap __aligned(8);
35	static bool hv_extended_cap_queried;
36	u64 status;
37
38	/*
39	 * Querying extended capabilities is an extended hypercall. Check if the
40	 * partition supports extended hypercall, first.
41	 */
42	if (!(ms_hyperv.priv_high & HV_ENABLE_EXTENDED_HYPERCALLS))
43		return false;
44
45	/* Extended capabilities do not change at runtime. */
46	if (hv_extended_cap_queried)
47		return hv_extended_cap & cap_query;
48
49	status = hv_do_hypercall(HV_EXT_CALL_QUERY_CAPABILITIES, NULL,
50				 &hv_extended_cap);
51
52	/*
53	 * The query extended capabilities hypercall should not fail under
54	 * any normal circumstances. Avoid repeatedly making the hypercall, on
55	 * error.
56	 */
57	hv_extended_cap_queried = true;
58	if (!hv_result_success(status)) {
59		pr_err("Hyper-V: Extended query capabilities hypercall failed 0x%llx\n",
60		       status);
61		return false;
62	}
63
64	return hv_extended_cap & cap_query;
65}
66EXPORT_SYMBOL_GPL(hv_query_ext_cap);