x86: VMware: Fix vmware_get_tsc code

Impact: Fix possible failure to calibrate the TSC on Vmware near 4 GHz

The current version of the code to get the tsc frequency from
the VMware hypervisor, will be broken on processor with frequency
(4G-1) HZ, because on such processors eax will have UINT_MAX
and that would be legitimate.
We instead check that EBX did change to decide if we were able to
read the frequency from the hypervisor.

Signed-off-by: Alok N Kataria <akataria@vmware.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/kernel/cpu/vmware.c

@@ -36,7 +36,7 @@
 			"=a"(eax), "=c"(ecx), "=d"(edx), "=b"(ebx) :	\
 			"0"(VMWARE_HYPERVISOR_MAGIC),			\
 			"1"(VMWARE_PORT_CMD_##cmd),			\
-			"2"(VMWARE_HYPERVISOR_PORT), "3"(0) :		\
+			"2"(VMWARE_HYPERVISOR_PORT), "3"(UINT_MAX) :	\
 			"memory");
 
 static inline int __vmware_platform(void)
@@ -53,7 +53,7 @@ static unsigned long __vmware_get_tsc_khz(void)
 
         VMWARE_PORT(GETHZ, eax, ebx, ecx, edx);
 
-        if (eax == (uint32_t)-1)
+        if (ebx == UINT_MAX)
                 return 0;
         tsc_hz = eax | (((uint64_t)ebx) << 32);
         do_div(tsc_hz, 1000);