linux-kernel - Re: [PATCH 2/4] Hypervisor detection and get tsc

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Date:	Mon, 03 Nov 2008 11:31:28 -0800
From:	Alok Kataria <akataria@...are.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Daniel Hecht <dhecht@...are.com>
Subject: Re: [PATCH 2/4] Hypervisor detection and get tsc_freq from
	hypervisor

Hi, 

The patch below fixes a problem with the implementation of
vmware_get_tsc_khz.

Please pick this patch too.

Thanks,
Alok

--

x86-VMware: Fix vmware_get_tsc code

From: Alok N Kataria <akataria@...are.com>

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@...are.com>
---

 arch/x86/kernel/cpu/vmware.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)


diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index 89bc346..b781e50 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/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);


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