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x86/boot: Introduce helpers for MSR reads/writes

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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
This commit is contained in:
Michael Roth 2022-02-09 12:09:59 -06:00 committed by Borislav Petkov
parent 6d3b3d34e3
commit 176db62257
3 changed files with 42 additions and 10 deletions
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26
arch/x86/boot/msr.h Normal file
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@ -0,0 +1,26 @@
/* 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 */

11
arch/x86/include/asm/msr.h
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@ -10,16 +10,7 @@
#include <asm/errno.h>
#include <asm/cpumask.h>
#include <uapi/asm/msr.h>
struct msr {
union {
struct {
u32 l;
u32 h;
};
u64 q;
};
};
#include <asm/shared/msr.h>
struct msr_info {
u32 msr_no;

15
arch/x86/include/asm/shared/msr.h Normal file
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@ -0,0 +1,15 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _ASM_X86_SHARED_MSR_H
#define _ASM_X86_SHARED_MSR_H
struct msr {
union {
struct {
u32 l;
u32 h;
};
u64 q;
};
};
#endif /* _ASM_X86_SHARED_MSR_H */