Re: problem wit svm_get_msr on kvm-kmod-2.6.31.6

[Jan Kiszka <jan.kiszka@siemens.com>]

Dietmar Maurer wrote:
> 00000000000037c0 <svm_get_msr>:
>     ...
> 
>     387e:       66 90                   xchg   %ax,%ax
>     3880:       0f 84 8a 00 00 00       je     3910 <svm_get_msr+0x150>
>     3886:       66 90                   xchg   %ax,%ax
>     3888:       0f 86 c2 01 00 00       jbe    3a50 <svm_get_msr+0x290>
>     388e:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>     3895:       48 8b 80 08 06 00 00    mov    0x608(%rax),%rax
>     389c:       48 89 02                mov    %rax,(%rdx)
>     389f:       90                      nop
>     38a0:       31 c0                   xor    %eax,%eax
>     38a2:       c3                      retq
>     38a3:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
>     38a8:       81 fe d9 01 00 00       cmp    $0x1d9,%esi
>     38ae:       0f 84 7c 00 00 00       je     3930 <svm_get_msr+0x170>
>     38b4:       0f 86 46 01 00 00       jbe    3a00 <svm_get_msr+0x240>
>     38ba:       81 fe db 01 00 00       cmp    $0x1db,%esi
>     38c0:       0f 84 ca 01 00 00       je     3a90 <svm_get_msr+0x2d0>
>     38c6:       81 fe dc 01 00 00       cmp    $0x1dc,%esi
>     38cc:       0f 1f 40 00             nopl   0x0(%rax)
>     38d0:       75 98                   jne    386a <svm_get_msr+0xaa>
>     38d2:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>     38d9:       48 8b 80 80 06 00 00    mov    0x680(%rax),%rax
>     38e0:       48 89 02                mov    %rax,(%rdx)
>     38e3:       eb bb                   jmp    38a0 <svm_get_msr+0xe0>
>     38e5:       0f 1f 00                nopl   (%rax)
>     38e8:       48 83 bf 78 28 00 00    cmpq   $0x0,0x2878(%rdi)
>     38ef:       00
>     38f0:       0f 85 82 01 00 00       jne    3a78 <svm_get_msr+0x2b8>
>     38f6:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>     38fd:       48 8b 48 50             mov    0x50(%rax),%rcx
>     3901:       0f 31                   rdtsc
>     3903:       48 01 c8                add    %rcx,%rax
> 
> # this is svm_get_msr+0x146
>     3906:       48 89 02                mov    %rax,(%rdx)
>     3909:       eb 95                   jmp    38a0 <svm_get_msr+0xe0>
>     390b:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
>     3910:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>     3917:       48 8b 80 00 06 00 00    mov    0x600(%rax),%rax
>     391e:       48 89 02                mov    %rax,(%rdx)
>     3921:       e9 7a ff ff ff          jmpq   38a0 <svm_get_msr+0xe0>
>     3926:       66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
>     392d:       00 00 00
>     3930:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>     3937:       48 8b 80 70 06 00 00    mov    0x670(%rax),%rax
>     393e:       48 89 02                mov    %rax,(%rdx)
>     3941:       e9 5a ff ff ff          jmpq   38a0 <svm_get_msr+0xe0>
>     3946:       66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
>     394d:       00 00 00
>     3950:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>     3957:       48 8b 80 28 06 00 00    mov    0x628(%rax),%rax
>     395e:       48 89 02                mov    %rax,(%rdx)
>     3961:       e9 3a ff ff ff          jmpq   38a0 <svm_get_msr+0xe0>
>     3966:       66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
>     396d:       00 00 00
>     3970:       48 c7 02 65 00 00 01    movq   $0x1000065,(%rdx)
>     3977:       e9 24 ff ff ff          jmpq   38a0 <svm_get_msr+0xe0>
>     397c:       0f 1f 40 00             nopl   0x0(%rax)
>     3980:       48 8b 87 e0 27 00 00    mov    0x27e0(%rdi),%rax
>     3987:       48 8b 80 10 06 00 00    mov    0x610(%rax),%rax
>     398e:       48 89 02                mov    %rax,(%rdx)
>     3991:       e9 0a ff ff ff          jmpq   38a0 <svm_get_msr+0xe0>
>     3996:       66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
>     399d:       00 00 00
>     ...
> 
> 
> We use the ubunto 2.6.24 kernel (http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-hardy.git;a=summary)
> 
> They have a few more patches applied:
> 
> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-hardy.git;a=history;f=include/asm-x86/msr.h;h=cfe169475b5b50a448326ef3c34f50100ac83faf;hb=HEAD
> 
> Maybe those last 2 patches can cause the problem?

Nope, it was most probably a kvm-kmod bug. Patch below should fix it.

Jan

----->

Fix native_read_tsc wrapping for x86-64

Use register constraint macros so that the return values of rdtsc are
properly picked up and no local variable is overwritten.

This is supposed to fix an oops on x86-64 with a 2.6.24 host kernel.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 x86/external-module-compat.h |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/x86/external-module-compat.h b/x86/external-module-compat.h
index b0b9f21..b0de024 100644
--- a/x86/external-module-compat.h
+++ b/x86/external-module-compat.h
@@ -94,9 +94,10 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
 
 static inline unsigned long long kvm_native_read_tsc(void)
 {
-	unsigned long long val;
-	asm volatile("rdtsc" : "=A" (val));
-	return val;
+	DECLARE_ARGS(val, low, high);
+
+	asm volatile("rdtsc" : EAX_EDX_RET(val, low, high));
+	return EAX_EDX_VAL(val, low, high);
 }
 
 #else /* >= 2.6.25 */
-- 
1.6.0.2