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

diff --git a/arch/x86/boot/msr.h b/arch/x86/boot/msr.h
new file mode 100644 (file)
index 0000000..aed66f7
--- /dev/null
+++ b/arch/x86/boot/msr.h
@@ -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 */

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index d42e6c6..65ec196 100644 (file)
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -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;

diff --git a/arch/x86/include/asm/shared/msr.h b/arch/x86/include/asm/shared/msr.h
new file mode 100644 (file)
index 0000000..1e6ec10
--- /dev/null
+++ b/arch/x86/include/asm/shared/msr.h
@@ -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 */