linux/drivers/hv/hv_common.c
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   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);
  67