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x86: VMware: Fix vmware_get_tsc code

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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>
This commit is contained in:
Alok Kataria 2008-11-03 11:31:28 -08:00 committed by H. Peter Anvin
parent 395628ef4e
commit 6bdbfe9991
1 changed files with 2 additions and 2 deletions
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4
arch/x86/kernel/cpu/vmware.c
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@ -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);