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>
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 48ad9d2..184d4a1 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -113,6 +113,9 @@
 
 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 @@
 	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 4fb37c8..1705944 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -168,7 +168,9 @@
 	   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 @@
 {
 	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 @@
 	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 @@
 	_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;