From: Michael Roth <[email protected]>
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.
Suggested-by: Borislav Petkov <[email protected]>
Signed-off-by: Michael Roth <[email protected]>
---
arch/x86/boot/msr.h | 28 ++++++++++++++++++++++++++++
arch/x86/include/asm/msr.h | 11 +----------
arch/x86/include/asm/shared/msr.h | 15 +++++++++++++++
3 files changed, 44 insertions(+), 10 deletions(-)
create mode 100644 arch/x86/boot/msr.h
create mode 100644 arch/x86/include/asm/shared/msr.h
diff --git a/arch/x86/boot/msr.h b/arch/x86/boot/msr.h
new file mode 100644
index 000000000000..b6bb2161da27
--- /dev/null
+++ b/arch/x86/boot/msr.h
@@ -0,0 +1,28 @@
+/* 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 tracepoint/exception handling infrastructure
+ * that's not available here, hence these boot_{rd,wr}msr helpers which serve
+ * the singular purpose of wrapping the RDMSR/WRMSR instructions to reduce the
+ * need for inline assembly calls throughout the boot kernel code.
+ */
+static inline void boot_rdmsr(unsigned int msr, struct msr *m)
+{
+ asm volatile("rdmsr" : "=a" (m->l), "=d" (m->h) : "c" (msr));
+}
+
+static inline void boot_wrmsr(unsigned int msr, const struct msr *m)
+{
+ asm volatile("wrmsr" : : "c" (msr), "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 d42e6c6b47b1..65ec1965cd28 100644
--- 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
index 000000000000..1e6ec10b3a15
--- /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 */
--
2.25.1
The following commit has been merged into the x86/sev branch of tip:
Commit-ID: 176db622573f028f85221873ea4577e096785315
Gitweb: https://git.kernel.org/tip/176db622573f028f85221873ea4577e096785315
Author: Michael Roth <[email protected]>
AuthorDate: Wed, 09 Feb 2022 12:09:59 -06:00
Committer: Borislav Petkov <[email protected]>
CommitterDate: Wed, 06 Apr 2022 12:59:17 +02:00
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 <[email protected]>
Signed-off-by: Michael Roth <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/boot/msr.h | 26 ++++++++++++++++++++++++++
arch/x86/include/asm/msr.h | 11 +----------
arch/x86/include/asm/shared/msr.h | 15 +++++++++++++++
3 files changed, 42 insertions(+), 10 deletions(-)
create mode 100644 arch/x86/boot/msr.h
create mode 100644 arch/x86/include/asm/shared/msr.h
diff --git a/arch/x86/boot/msr.h b/arch/x86/boot/msr.h
new file mode 100644
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
--- 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
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 */