Re: [tip:x86/urgent] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit

Borislav Petkov
2009-08-22T16:37:57Z

On Fri, Aug 21, 2009 at 10:40:18AM -0700, H. Peter Anvin wrote:
> If we're going to modify the paravirt_crap for yet another MSR
> operation, then let's at least make it something like "write_msr_edi"
> and have it take a parameter for the EDI value. Perhaps we should let
> it set EBX and ESI as well (and the same for the read operation, even
> though it already exists.)

Ok, how about making all rdmsr* variants indirectly call into a
native_read_msr_safe_reg() helper which takes esi and edi as additional
arguments. There was no room for ebx since paravirt has a PVOP_CALL4
macro which takes the largest number of args - 4 and I am lazy, of
course, to implement a PVOP_CALL5 thing :o)

The wrmsr variants could be done similarly.

Suggestions, comments?

--
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index 48ad9d2..2fec363 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -55,8 +55,10 @@ static inline unsigned long long native_read_msr(unsigned int msr)
return EAX_EDX_VAL(val, low, high);
}

-static inline unsigned long long native_read_msr_safe(unsigned int msr,
- int *err)
+static inline unsigned long long native_read_msr_safe_reg(unsigned int msr,
+ int *err,
+ unsigned int edi,
+ unsigned int esi)
{
DECLARE_ARGS(val, low, high);

@@ -67,24 +69,15 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
".previous\n\t"
_ASM_EXTABLE(2b, 3b)
: [err] "=r" (*err), EAX_EDX_RET(val, low, high)
- : "c" (msr), [fault] "i" (-EFAULT));
+ : "c" (msr), [fault] "i" (-EFAULT), "D" (edi), "S" (esi));
+
return EAX_EDX_VAL(val, low, high);
}

-static inline unsigned long long native_read_msr_amd_safe(unsigned int msr,
+static inline unsigned long long native_read_msr_safe(unsigned int msr,
int *err)
{
- DECLARE_ARGS(val, low, high);
-
- asm volatile("2: rdmsr ; xor %0,%0\n"
- "1:\n\t"
- ".section .fixup,\"ax\"\n\t"
- "3: mov %3,%0 ; jmp 1b\n\t"
- ".previous\n\t"
- _ASM_EXTABLE(2b, 3b)
- : "=r" (*err), EAX_EDX_RET(val, low, high)
- : "c" (msr), "D" (0x9c5a203a), "i" (-EFAULT));
- return EAX_EDX_VAL(val, low, high);
+ return native_read_msr_safe_reg(msr, err, 0, 0);
}

static inline void native_write_msr(unsigned int msr,
@@ -181,11 +174,12 @@ static inline int rdmsrl_safe(unsigned msr, unsigned long long *p)
*p = native_read_msr_safe(msr, &err);
return err;
}
+
static inline int rdmsrl_amd_safe(unsigned msr, unsigned long long *p)
{
int err;

- *p = native_read_msr_amd_safe(msr, &err);
+ *p = native_read_msr_safe_reg(msr, &err, 0x9c5a203a, 0);
return err;
}

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 4fb37c8..d49e1ee 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -166,8 +166,9 @@ struct pv_cpu_ops {

/* MSR, PMC and TSR operations.
err = 0/-EFAULT. wrmsr returns 0/-EFAULT. */
- u64 (*read_msr_amd)(unsigned int msr, int *err);
u64 (*read_msr)(unsigned int msr, int *err);
+ u64 (*read_msr_reg)(unsigned int msr, int *err, unsigned edi,
+ unsigned esi);
int (*write_msr)(unsigned int msr, unsigned low, unsigned high);

u64 (*read_tsc)(void);
@@ -820,9 +821,10 @@ static inline u64 paravirt_read_msr(unsigned msr, int *err)
{
return PVOP_CALL2(u64, pv_cpu_ops.read_msr, msr, err);
}
-static inline u64 paravirt_read_msr_amd(unsigned msr, int *err)
+static inline u64 paravirt_read_msr_reg(unsigned msr, int *err, unsigned edi,
+ unsigned esi)
{
- return PVOP_CALL2(u64, pv_cpu_ops.read_msr_amd, msr, err);
+ return PVOP_CALL4(u64, pv_cpu_ops.read_msr_reg, msr, err, edi, esi);
}
static inline int paravirt_write_msr(unsigned msr, unsigned low, unsigned high)
{
@@ -873,7 +875,7 @@ static inline int rdmsrl_amd_safe(unsigned msr, unsigned long long *p)
{
int err;

- *p = paravirt_read_msr_amd(msr, &err);
+ *p = paravirt_read_msr_reg(msr, &err, 0x9c5a203a, 0);
return err;
}

diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 70ec9b9..ecac58d 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -362,7 +362,7 @@ struct pv_cpu_ops pv_cpu_ops = {
#endif
.wbinvd = native_wbinvd,
.read_msr = native_read_msr_safe,
- .read_msr_amd = native_read_msr_amd_safe,
+ .read_msr_reg = native_read_msr_safe_reg,
.write_msr = native_write_msr_safe,
.read_tsc = native_read_tsc,
.read_pmc = native_read_pmc,

--
Regards/Gruss,
Boris.