linux/arch/x86/boot/msr.h
Michael Roth 176db62257 x86/boot: Introduce helpers for MSR reads/writes
The current set of helpers used throughout the run-time kernel have
dependencies on code/facilities outside of the boot kernel, so there
are a number of call-sites throughout the boot kernel where inline
assembly is used instead. More will be added with subsequent patches
that add support for SEV-SNP, so take the opportunity to provide a basic
set of helpers that can be used by the boot kernel to reduce reliance on
inline assembly.

Use boot_* prefix so that it's clear these are helpers specific to the
boot kernel to avoid any confusion with the various other MSR read/write
helpers.

  [ bp: Disambiguate parameter names and trim comment. ]

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-6-brijesh.singh@amd.com
2022-04-06 12:59:17 +02:00

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C

/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Helpers/definitions related to MSR access.
*/
#ifndef BOOT_MSR_H
#define BOOT_MSR_H
#include <asm/shared/msr.h>
/*
* The kernel proper already defines rdmsr()/wrmsr(), but they are not for the
* boot kernel since they rely on tracepoint/exception handling infrastructure
* that's not available here.
*/
static inline void boot_rdmsr(unsigned int reg, struct msr *m)
{
asm volatile("rdmsr" : "=a" (m->l), "=d" (m->h) : "c" (reg));
}
static inline void boot_wrmsr(unsigned int reg, const struct msr *m)
{
asm volatile("wrmsr" : : "c" (reg), "a"(m->l), "d" (m->h) : "memory");
}
#endif /* BOOT_MSR_H */