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From: Tom Lendacky <thomas.lendacky@amd.com>
To: Jim Mattson <jmattson@google.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Joerg Roedel <joro@8bytes.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	X86 ML <x86@kernel.org>,
	"Chang S. Bae" <chang.seok.bae@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sasha Levin <sashal@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: FSGSBASE causing panic on 5.9-rc1
Date: Thu, 20 Aug 2020 14:05:16 -0500	[thread overview]
Message-ID: <e8b3f80e-3c5a-7a03-97f9-75cbdbbb023c@amd.com> (raw)
In-Reply-To: <c4cc63b5-2861-5370-781f-5d664b6ffed5@amd.com>



On 8/20/20 2:04 PM, Tom Lendacky wrote:
> On 8/20/20 1:41 PM, Tom Lendacky wrote:
>> On 8/20/20 1:39 PM, Jim Mattson wrote:
>>> On Thu, Aug 20, 2020 at 11:38 AM Jim Mattson <jmattson@google.com> wrote:
>>>>
>>>> On Thu, Aug 20, 2020 at 11:34 AM Tom Lendacky 
>>>> <thomas.lendacky@amd.com> wrote:
>>>>>
>>>>>
>>>>> Bisecting with unsafe_fsgsbase identified:
>>>>>
>>>>> c82965f9e530 ("x86/entry/64: Handle FSGSBASE enabled paranoid 
>>>>> entry/exit")
>>>>>
>>>>> But I'm thinking that could be because it starts using GET_PERCPU_BASE,
>>>>> which on Rome would use RDPID. So is SVM restoring TSC_AUX_MSR too late?
>>>>> That would explain why I don't see the issue on Naples, which doesn't
>>>>> support RDPID.
>>>>
>>>> It looks to me like SVM loads the guest TSC_AUX from vcpu_load to
>>>> vcpu_put, with this comment:
>>>>
>>>> /* This assumes that the kernel never uses MSR_TSC_AUX */
>>>> if (static_cpu_has(X86_FEATURE_RDTSCP))
>>>>          wrmsrl(MSR_TSC_AUX, svm->tsc_aux);
>>>
>>> Correction: It never restores TSC_AUX, AFAICT.
>>
>> It does, it's in the host_save_user_msrs array.
> 
> I added a quick hack to save TSC_AUX to a new variable in the SVM struct 
> and then restore it right after VMEXIT (just after where GS is restored in 
> svm_vcpu_enter_exit()) and my guest is no longer crashing.

Sorry, I mean my host is no longer crashing.

Thanks,
Tom

> 
> Thanks,
> Tom
> 
>>
>> Thanks,
>> Tom
>>
>>>

  reply	other threads:[~2020-08-20 19:05 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19 18:07 FSGSBASE causing panic on 5.9-rc1 Tom Lendacky
2020-08-19 18:19 ` Tom Lendacky
2020-08-19 21:25   ` Andy Lutomirski
2020-08-20  0:21     ` Andy Lutomirski
2020-08-20 15:10       ` Sean Christopherson
2020-08-20 15:21         ` Tom Lendacky
2020-08-20 15:55           ` Andy Lutomirski
2020-08-20 16:17             ` Tom Lendacky
2020-08-20 16:30               ` Tom Lendacky
2020-08-20 17:41                 ` Paolo Bonzini
2020-08-20 18:34                 ` Tom Lendacky
2020-08-20 18:38                   ` Jim Mattson
2020-08-20 18:39                     ` Jim Mattson
2020-08-20 18:41                       ` Tom Lendacky
2020-08-20 19:04                         ` Tom Lendacky
2020-08-20 19:05                           ` Tom Lendacky [this message]
2020-08-20 20:07                             ` Dave Hansen
2020-08-20 20:15                               ` Tom Lendacky
2020-08-20 20:36                                 ` Andy Lutomirski
2020-08-20 22:05                                   ` Sean Christopherson
2020-08-20 22:07                                     ` Andy Lutomirski
2020-08-20 22:34                                       ` Sean Christopherson
2020-08-21  0:00                                         ` Tom Lendacky
2020-08-21  1:56                                           ` Sean Christopherson
2020-08-20 18:43           ` Bae, Chang Seok
2020-08-20 13:43     ` Paolo Bonzini
2020-08-20 17:51       ` Andy Lutomirski

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