In the __getcpu function, lsl was using the wrong target and destination registers. Luckily, the compiler tends to choose %eax for both variables, so it has been working so far.
Cc: x86@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Samuel Neves sneves@dei.uc.pt --- arch/x86/include/asm/vgtod.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h index fb856c9f0449..53748541c487 100644 --- a/arch/x86/include/asm/vgtod.h +++ b/arch/x86/include/asm/vgtod.h @@ -93,7 +93,7 @@ static inline unsigned int __getcpu(void) * * If RDPID is available, use it. */ - alternative_io ("lsl %[p],%[seg]", + alternative_io ("lsl %[seg],%[p]", ".byte 0xf3,0x0f,0xc7,0xf8", /* RDPID %eax/rax */ X86_FEATURE_RDPID, [p] "=a" (p), [seg] "r" (__PER_CPU_SEG));
On Sat, Sep 1, 2018 at 1:14 PM, Samuel Neves sneves@dei.uc.pt wrote:
In the __getcpu function, lsl was using the wrong target and destination registers. Luckily, the compiler tends to choose %eax for both variables, so it has been working so far.
Cc: x86@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Samuel Neves sneves@dei.uc.pt
Acked-by: Andy Lutomirski luto@kernel.org Fixes: a582c540ac1b ("x86/vdso: Use RDPID in preference to LSL when available")
Whoops! I even wrote a selftest just for the offending commit, but, of course, the selftest passes :( I tested this by giving gcc some gentle encouragement to allocate different registers, and the existing code is indeed wrong and the fix indeed fixes it.
--Andy
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