From: Andy Lutomirski <luto@amacapital.net>
To: Jim Mattson <jmattson@google.com>
Cc: "Andy Lutomirski" <luto@kernel.org>,
"Kyle Huey" <me@kylehuey.com>,
"Robert O'Callahan" <robert@ocallahan.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>, "X86 ML" <x86@kernel.org>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Jeff Dike" <jdike@addtoit.com>,
"Richard Weinberger" <richard@nod.at>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Shuah Khan" <shuah@kernel.org>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Borislav Petkov" <bp@suse.de>,
"Peter Zijlstra" <peterz@infradead.org>,
"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
"Len Brown" <len.brown@intel.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
"Dmitry Safonov" <dsafonov@virtuozzo.com>,
"David Matlack" <dmatlack@google.com>,
"Nadav Amit" <nadav.amit@gmail.com>,
"Andi Kleen" <andi@firstfloor.org>,
LKML <linux-kernel@vger.kernel.org>,
user-mode-linux-devel@lists.sourceforge.net,
"open list:USER-MODE LINUX (UML)"
<user-mode-linux-user@lists.sourceforge.net>,
"Linux FS Devel" <linux-fsdevel@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
"kvm list" <kvm@vger.kernel.org>
Subject: Re: [PATCH v14 8/9] KVM: x86: virtualize cpuid faulting
Date: Fri, 27 Jul 2018 13:46:06 -0700 [thread overview]
Message-ID: <6F48D384-B29C-41B4-83F1-B02FC2480205@amacapital.net> (raw)
In-Reply-To: <CALMp9eSyJep6UPxeiZRWPrdzwvvcqJEbPPZ6C61EeHsvdyhMLg@mail.gmail.com>
> On Jul 27, 2018, at 1:28 PM, Jim Mattson <jmattson@google.com> wrote:
>
>> On Fri, Jul 27, 2018 at 12:41 PM, Andy Lutomirski <luto@kernel.org> wrote:
>>> On Wed, Feb 8, 2017 at 12:09 AM, Kyle Huey <me@kylehuey.com> wrote:
>>> Hardware support for faulting on the cpuid instruction is not required to
>>> emulate it, because cpuid triggers a VM exit anyways. KVM handles the relevant
>>> MSRs (MSR_PLATFORM_INFO and MSR_MISC_FEATURES_ENABLE) and upon a
>>> cpuid-induced VM exit checks the cpuid faulting state and the CPL.
>>> kvm_require_cpl is even kind enough to inject the GP fault for us.
>>>
>>> Signed-off-by: Kyle Huey <khuey@kylehuey.com>
>>> Reviewed-by: David Matlack <dmatlack@google.com>
>>> ---
>>> ...
>>> @@ -7613,16 +7636,19 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>>>
>>> kvm_clear_async_pf_completion_queue(vcpu);
>>> kvm_async_pf_hash_reset(vcpu);
>>> vcpu->arch.apf.halted = false;
>>>
>>> if (!init_event) {
>>> kvm_pmu_reset(vcpu);
>>> vcpu->arch.smbase = 0x30000;
>>> +
>>> + vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
>>> + vcpu->arch.msr_misc_features_enables = 0;
>>
>> Jim, I assume you're worried about this bit? It seems like
>> msr_platform_info should maybe be initialized to zero to avoid causing
>> an unintended migration issue.
>
> Initializing this bit to zero helps with migration, but then if the
> CPUID faulting bits in both MSRs are set, userspace has to take pains
> to ensure that MSR_PLATFORM_INFO is restored first, or the
> MSR_MISC_FEATURES_ENABLES value will be rejected.
The code could drop the constraint and just let the entry possibly fail if the MSRs are set wrong
>
> I'm also concerned about the 0 in the "Maximum Non-Turbo Ratio" field
> feeding into someone's calculated TSC frequency.
Hmm. I don’t have a good answer to that. Are there any real CPUs that have this MSR but don’t have that field?
next prev parent reply other threads:[~2018-07-27 20:46 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-08 8:09 [PATCH v14 0/9] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction Kyle Huey
2017-02-08 8:09 ` [PATCH v14 1/9] x86/arch_prctl/64: Use SYSCALL_DEFINE2 to define sys_arch_prctl Kyle Huey
2017-02-08 8:09 ` [PATCH v14 2/9] x86/arch_prctl/64: Rename do_arch_prctl to do_arch_prctl_64 Kyle Huey
2017-02-08 8:09 ` [PATCH v14 3/9] x86/arch_prctl: Add do_arch_prctl_common Kyle Huey
2017-02-08 8:09 ` [PATCH v14 4/9] x86/syscalls/32: Wire up arch_prctl on x86-32 Kyle Huey
2017-02-08 8:09 ` [PATCH v14 5/9] x86/cpufeature: Detect CPUID faulting support Kyle Huey
2017-02-08 8:09 ` [PATCH v14 6/9] x86/arch_prctl: Add ARCH_[GET|SET]_CPUID Kyle Huey
2017-02-08 8:09 ` [PATCH v14 7/9] x86/arch_prctl: Selftest for ARCH_[GET|SET]_CPUID Kyle Huey
2017-02-08 8:09 ` [PATCH v14 8/9] KVM: x86: virtualize cpuid faulting Kyle Huey
2018-07-27 17:15 ` Jim Mattson
2018-07-27 19:41 ` Andy Lutomirski
2018-07-27 20:28 ` Jim Mattson
2018-07-27 20:46 ` Andy Lutomirski [this message]
2018-07-27 21:03 ` Jim Mattson
2018-07-27 21:05 ` Andy Lutomirski
2018-07-27 21:30 ` Jim Mattson
2018-07-27 22:58 ` Andy Lutomirski
2017-02-08 8:09 ` [PATCH v14 9/9] x86/arch_prctl: Rename 'code' argument to 'option' Kyle Huey
2017-02-10 13:07 ` [PATCH v14 0/9] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction Thomas Gleixner
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