Message-ID: <CANRm+CxvBqauRuddRig03_fwdhPpxBh2z17vG0rnHmHMjxrwJQ@mail.gmail.com>
Date:	Tue, 21 Jun 2016 21:59:20 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Yu Chen <yu.chen.surf@...il.com>,
	kernel test robot <xiaolong.ye@...el.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	linux-acpi@...r.kernel.org, Len Brown <len.brown@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Radim Krcmar <rkrcmar@...hat.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Zhang Rui <rui.zhang@...el.com>, lkp@...org
Subject: Re: [LKP] [lkp] [x86 tsc] 19fa5e7364: WARNING: CPU: 0 PID: 0 at
 arch/x86/mm/extable.c:50 ex_handler_rdmsr_unsafe+0x72/0x80

Hi Paolo,
2016-06-21 18:24 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
> 2016-06-21 18:10 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>>
>>
>> On 21/06/2016 08:08, Wanpeng Li wrote:
>>> Cc KVM ML, Paolo, Radim,
>>>>> FYI, raw QEMU command line is:
>>>>>
>>>>>         qemu-system-x86_64 -enable-kvm -cpu SandyBridge -kernel /pkg/linux/x86_64-randconfig-w0-06180628/gcc-6/19fa5e73647fde1e6a7038a8f05cddf4c43f08d3/vmlinuz-4.7.0-rc3-00009-g19fa5e7 -append 'root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-kbuild-yocto-x86_64-32/bisect_boot-1-yocto-minimal-x86_64.cgz-x86_64-randconfig-w0-06180628-19fa5e73647fde1e6a7038a8f05cddf4c43f08d3-20160618-25535-h82bax-0.yaml~ ARCH=x86_64 kconfig=x86_64-randconfig-w0-06180628 branch=internal-eywa/master commit=19fa5e73647fde1e6a7038a8f05cddf4c43f08d3 BOOT_IMAGE=/pkg/linux/x86_64-randconfig-w0-06180628/gcc-6/19fa5e73647fde1e6a7038a8f05cddf4c43f08d3/vmlinuz-4.7.0-rc3-00009-g19fa5e7 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-kbuild-yocto-x86_64/yocto-minimal-x86_64.cgz/x86_64-randconfig-w0-06180628/gcc-6/19fa5e73647fde1e6a7038a8f05cddf4c43f08d3/0 LKP_SERVER=inn earlyprintk=ttyS0,115200 systemd.log_level=err debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 console=ttyS0,115200 console=tty0 vga=normal rw ip=::::vm-kbuild-yocto-x86_64-32::dhcp drbd.minor_count=8'  -initrd /fs/sdh1/initrd-vm-kbuild-yocto-x86_64-32 -m 320 -smp 1 -device e1000,netdev=net0 -netdev user,id=net0 -boot order=nc -no-reboot -watchdog i6300esb -rtc base=localtime -drive file=/fs/sdh1/disk0-vm-kbuild-yocto-x86_64-32,media=disk,if=virtio -pidfile /dev/shm/kboot/pid-vm-kbuild-yocto-x86_64-32 -serial file:/dev/shm/kboot/serial-vm-kbuild-yocto-x86_64-32 -daemonize -display none -monitor null
>>>>>
>>>> This  problem was caused due to kvm does not support MSR_PLATFORM_INFO(0xce),
>>>> according to Wanpeng's feedback.
>>>>
>>>> Hi Wanpeng, is it possible for kvm to simulate this MSR, otherwise we
>>>> might have to use
>>>> rdmsr_safe instead.
>>>
>>> There is a thread discussed this before
>>> https://patchwork.kernel.org/patch/8833021/, MSR_PLATFORM_INFO can't
>>> be simple emulation.
>>>
>>> Ping Paolo, Radim. :)
>>
>> rdmsr_safe must be used instead.  I'll prepare a patch.
>
> Actually I have such a patch on hand under testing, I will send out soon. :)

I have a temporal patch as below, it seems that guest tsc(~300MHz) is
still not correct and guest kernel panic during boot w/ message
"MP-BIOS bug: 8254 timer not connect to IO-APIC, kernel-panic - not
syncing: IOAPIC + timer doesn't work" etc. Any proposal to improve my
patch is a great appreciated. :) 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

--------------------

>From 8033ae4c7e44d6bfe26642b151de03c613125066 Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@...mail.com>
Date: Tue, 21 Jun 2016 19:41:12 +0800
Subject: [PATCH] x86: fix rdmsr MSR_PLATFORM_INFO unsafe warning in kvm guest

From: Wanpeng Li <wanpeng.li@...mail.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.

Reported-by: kernel test robot <xiaolong.ye@...el.com>
Cc: Len Brown <len.brown@...el.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: Zhang Rui <rui.zhang@...el.com>
Cc: Chen Yu <y.c.chen@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: jacob.jun.pan@...el.com
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
 arch/x86/kernel/tsc_msr.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c
index e0c2b30..15e06e1 100644
--- a/arch/x86/kernel/tsc_msr.c
+++ b/arch/x86/kernel/tsc_msr.c
@@ -123,8 +123,11 @@ 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)) {
+ rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
+ ratio = (hi >> 8) & 0x1f;
+ } else
+ ratio = (lo >> 8) & 0xff;

 done:
  /* TSC frequency = maximum resolved freq * maximum resolved bus ratio */
-- 
1.9.1

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