x86, msr: Add rd/wrmsr interfaces with preset registers

native_{rdmsr,wrmsr}_safe_regs are two new interfaces which allow
presetting of a subset of eight x86 GPRs before executing the rd/wrmsr
instructions. This is needed at least on AMD K8 for accessing an erratum
workaround MSR.

Originally based on an idea by H. Peter Anvin.

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
LKML-Reference: <1251705011-18636-1-git-send-email-petkovbb@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

2 files changed, 29 insertions, 0 deletions

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 48ad9d29484a..184d4a113961 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -113,6 +113,9 @@ notrace static inline int native_write_msr_safe(unsigned int msr,
 
 extern unsigned long long native_read_tsc(void);
 
+extern int native_rdmsr_safe_regs(u32 *regs);
+extern int native_wrmsr_safe_regs(u32 *regs);
+
 static __always_inline unsigned long long __native_read_tsc(void)
 {
         DECLARE_ARGS(val, low, high);
@@ -189,6 +192,16 @@ static inline int rdmsrl_amd_safe(unsigned msr, unsigned long long *p)
         return err;
 }
 
+static inline int rdmsr_safe_regs(u32 *regs)
+{
+        return native_rdmsr_safe_regs(regs);
+}
+
+static inline int wrmsr_safe_regs(u32 *regs)
+{
+        return native_wrmsr_safe_regs(regs);
+}
+
 #define rdtscl(low)                                             \
         ((low) = (u32)__native_read_tsc())
 
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 4fb37c8a0832..1705944e0374 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -168,7 +168,9 @@ struct pv_cpu_ops {
            err = 0/-EFAULT.  wrmsr returns 0/-EFAULT. */
         u64 (*read_msr_amd)(unsigned int msr, int *err);
         u64 (*read_msr)(unsigned int msr, int *err);
+        int (*rdmsr_regs)(u32 *regs);
         int (*write_msr)(unsigned int msr, unsigned low, unsigned high);
+        int (*wrmsr_regs)(u32 *regs);
 
         u64 (*read_tsc)(void);
         u64 (*read_pmc)(int counter);
@@ -820,6 +822,12 @@ static inline u64 paravirt_read_msr(unsigned msr, int *err)
 {
         return PVOP_CALL2(u64, pv_cpu_ops.read_msr, msr, err);
 }
+
+static inline int paravirt_rdmsr_regs(u32 *regs)
+{
+        return PVOP_CALL1(int, pv_cpu_ops.rdmsr_regs, regs);
+}
+
 static inline u64 paravirt_read_msr_amd(unsigned msr, int *err)
 {
         return PVOP_CALL2(u64, pv_cpu_ops.read_msr_amd, msr, err);
@@ -829,6 +837,11 @@ static inline int paravirt_write_msr(unsigned msr, unsigned low, unsigned high)
         return PVOP_CALL3(int, pv_cpu_ops.write_msr, msr, low, high);
 }
 
+static inline int paravirt_wrmsr_regs(u32 *regs)
+{
+        return PVOP_CALL1(int, pv_cpu_ops.wrmsr_regs, regs);
+}
+
 /* These should all do BUG_ON(_err), but our headers are too tangled. */
 #define rdmsr(msr, val1, val2)                  \
 do {                                            \
@@ -862,6 +875,9 @@ do {						\
         _err;                                   \
 })
 
+#define rdmsr_safe_regs(regs)   paravirt_rdmsr_regs(regs)
+#define wrmsr_safe_regs(regs)   paravirt_wrmsr_regs(regs)
+
 static inline int rdmsrl_safe(unsigned msr, unsigned long long *p)
 {
         int err;