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[PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

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  [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest Wanpeng Li <kernellwp@gmail.com> - 2016-06-22 03:30 +0200
    Re: [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm  guest Paolo Bonzini <pbonzini@redhat.com> - 2016-06-22 19:50 +0200
    Re: [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm  guest Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 09:20 +0200
      Re: [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest Wanpeng Li <kernellwp@gmail.com> - 2016-06-23 09:30 +0200
        Re: [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest Wanpeng Li <kernellwp@gmail.com> - 2016-06-23 09:40 +0200
      Re: [LKP] [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in  kvm guest Yu Chen <yu.chen.surf@gmail.com> - 2016-06-23 09:40 +0200
        Re: [LKP] [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in  kvm guest Wanpeng Li <kernellwp@gmail.com> - 2016-06-23 09:50 +0200
          Re: [LKP] [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in  kvm guest Wanpeng Li <kernellwp@gmail.com> - 2016-06-23 10:10 +0200

#1428317 — [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

From: Wanpeng Li <wanpeng.li@hotmail.com>

------------[ cut here ]------------
WARNING: CPU: 0 PID: 0 at arch/x86/mm/extable.c:50 ex_handler_rdmsr_unsafe+0x6a/0x70
unchecked MSR access error: RDMSR from 0xce
Modules linked in:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.7.0-rc3+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 0000000000000000 ffffffff81c03ce0 ffffffff813b3eae ffffffff81c03d30
 0000000000000000 ffffffff81c03d20 ffffffff81067181 0000003200000001
 ffffffff81c03df8 ffffffff8179676c 0000000000000000 ffffffff81fcd2c0
Call Trace:
 dump_stack+0x67/0x99
 __warn+0xd1/0xf0
 warn_slowpath_fmt+0x4f/0x60
 ex_handler_rdmsr_unsafe+0x6a/0x70
 fixup_exception+0x39/0x50
 do_general_protection+0x93/0x1b0
 general_protection+0x22/0x30
 ? cpu_khz_from_msr+0xd8/0x1c0
 native_calibrate_cpu+0x30/0x5b0
 tsc_init+0x2b/0x297
 x86_late_time_init+0xf/0x11
 start_kernel+0x398/0x451
 ? set_init_arg+0x55/0x55
 x86_64_start_reservations+0x2f/0x31
 x86_64_start_kernel+0xea/0xed

After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core 
Architecture"), rdmsr MSR_PLATFORM_INFO is used to get maximum non-turbo 
ratio for recent Intel Core Architecture which results in kvm guest rdmsr 
unsafe warning.

As Radim pointed out before:

| MSR_PLATFORM_INFO: Intel changes it from family to family and there is
| no obvious overlap or default.  If we picked 0 (any other fixed value),
| then the guest would have to know that 0 doesn't mean that
| MSR_PLATFORM_INFO returned 0, but that KVM doesn't emulate this MSR and
| the value cannot be used.  This is very similar to handling a #GP in the
| guest, but also has a disadvantage, because KVM cannot say that
| MSR_PLATFORM_INFO is 0.  Simple emulation is not possible.

This patch fix it by using rdmsr_safe to read MSR_PLATFORM_INFO in kvm 
guest in order that #GP can be fixed up, then tsc will be calibrated by 
PIT, HPET etc.

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Chen Yu <y.c.chen@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: jacob.jun.pan@intel.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 arch/x86/kernel/tsc_msr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c
index e0c2b30..e6e465e 100644
--- a/arch/x86/kernel/tsc_msr.c
+++ b/arch/x86/kernel/tsc_msr.c
@@ -70,7 +70,7 @@ static int match_cpu(u8 family, u8 model)
  */
 unsigned long cpu_khz_from_msr(void)
 {
-	u32 lo, hi, ratio, freq_id, freq;
+	u32 lo, hi, freq_id, freq, ratio = 0;
 	unsigned long res;
 	int cpu_index;
 
@@ -123,8 +123,8 @@ unsigned long cpu_khz_from_msr(void)
 	}
 
 get_ratio:
-	rdmsr(MSR_PLATFORM_INFO, lo, hi);
-	ratio = (lo >> 8) & 0xff;
+	if (!rdmsr_safe(MSR_PLATFORM_INFO, &lo, &hi))
+		ratio = (lo >> 8) & 0xff;
 
 done:
 	/* TSC frequency = maximum resolved freq * maximum resolved bus ratio */
-- 
1.9.1

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#1429027 — Re: [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

On 22/06/2016 03:28, Wanpeng Li wrote:
>  
>  get_ratio:
> -	rdmsr(MSR_PLATFORM_INFO, lo, hi);
> -	ratio = (lo >> 8) & 0xff;
> +	if (!rdmsr_safe(MSR_PLATFORM_INFO, &lo, &hi))
> +		ratio = (lo >> 8) & 0xff;

This looks good, thanks.

Paolo

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#1429517 — Re: [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

On Wed, 22 Jun 2016, Wanpeng Li wrote:
> After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core 

Where did you find that commit? It's neither in Linus tree nor in tip.

Thanks,

	tglx

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#1429518

2016-06-23 15:09 GMT+08:00 Thomas Gleixner <tglx@linutronix.de>:
> On Wed, 22 Jun 2016, Wanpeng Li wrote:
>> After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core
>
> Where did you find that commit? It's neither in Linus tree nor in tip.

It is reported by lkp. https://lkml.org/lkml/2016/6/20/110 The patch
is against x86 branch on Len Brown's tree. And try to fix this commit:
https://git.kernel.org/cgit/linux/kernel/git/lenb/linux.git/commit/?h=x86&id=fc141535ad8a67fd58623289c04e35465e2a07f2

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#1429533

Hi Jacob,
2016-06-23 15:28 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> 2016-06-23 15:09 GMT+08:00 Thomas Gleixner <tglx@linutronix.de>:
>> On Wed, 22 Jun 2016, Wanpeng Li wrote:
>>> After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core
>>
>> Where did you find that commit? It's neither in Linus tree nor in tip.
>
> It is reported by lkp. https://lkml.org/lkml/2016/6/20/110 The patch
> is against x86 branch on Len Brown's tree. And try to fix this commit:
> https://git.kernel.org/cgit/linux/kernel/git/lenb/linux.git/commit/?h=x86&id=fc141535ad8a67fd58623289c04e35465e2a07f2

I prefer this patch can be applied separately instead of fold into the
bad commit since it shows the issue when access MSR_PLATFORM_INFO in
kvm guest and other guys who want to access MSR_PLATFORM_INFO later
can find the changelog and make better decisions.

Regards,
Wanpeng Li

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#1429531 — Re: [LKP] [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

On Thu, Jun 23, 2016 at 3:09 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> On Wed, 22 Jun 2016, Wanpeng Li wrote:
>> After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core
>
> Where did you find that commit? It's neither in Linus tree nor in tip.
>
It is in Len's tree, we are planing to resend the patchset with Wanpeng's fix
merged with a credit to him in commit msg, thanks for Wanpeng's effort.
thanks all.

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#1429536 — Re: [LKP] [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

Hi Yu，
2016-06-23 15:37 GMT+08:00 Yu Chen <yu.chen.surf@gmail.com>:
> On Thu, Jun 23, 2016 at 3:09 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>> On Wed, 22 Jun 2016, Wanpeng Li wrote:
>>> After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core
>>
>> Where did you find that commit? It's neither in Linus tree nor in tip.
>>
> It is in Len's tree, we are planing to resend the patchset with Wanpeng's fix
> merged with a credit to him in commit msg, thanks for Wanpeng's effort.
> thanks all.

I prefer this patch can be applied separately instead of fold into the
bad commit since it shows the issue when access MSR_PLATFORM_INFO in
kvm guest and other guys who want to access MSR_PLATFORM_INFO later
can find the changelog and make better decisions.

Regards,
Wanpeng Li

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#1429555 — Re: [LKP] [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

2016-06-23 15:41 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> Hi Yu，
> 2016-06-23 15:37 GMT+08:00 Yu Chen <yu.chen.surf@gmail.com>:
>> On Thu, Jun 23, 2016 at 3:09 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>>> On Wed, 22 Jun 2016, Wanpeng Li wrote:
>>>> After commit (fc141535ad8 : "x86 tsc_msr: Extend to include Intel Core
>>>
>>> Where did you find that commit? It's neither in Linus tree nor in tip.
>>>
>> It is in Len's tree, we are planing to resend the patchset with Wanpeng's fix
>> merged with a credit to him in commit msg, thanks for Wanpeng's effort.
>> thanks all.
>
> I prefer this patch can be applied separately instead of fold into the
> bad commit since it shows the issue when access MSR_PLATFORM_INFO in
> kvm guest and other guys who want to access MSR_PLATFORM_INFO later
> can find the changelog and make better decisions.

Thomas, does it make sense to keep separate?

Regards,
Wanpeng Li

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