From: Xiaoyao Li <xiaoyao.li@intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/7] KVM: VMX: Check Intel PT related CPUID leaves
Date: Tue, 19 Oct 2021 09:46:29 +0800 [thread overview]
Message-ID: <b9b72305-d05e-bb60-ab24-7d4eb45182e3@intel.com> (raw)
In-Reply-To: <YW2uUcor5nhDZ3DS@google.com>
On 10/19/2021 1:26 AM, Sean Christopherson wrote:
> On Mon, Oct 18, 2021, Xiaoyao Li wrote:
>> On 10/18/2021 8:47 PM, Paolo Bonzini wrote:
>>>>> One option would be to bump that to the theoretical max of 15,
>>>>> which doesn't seem too horrible, especially if pt_desc as a whole
>>>>> is allocated on-demand, which it probably should be since it isn't
>>>>> exactly tiny (nor ubiquitous)
>>>>>
>>>>> A different option would be to let userspace define whatever it
>>>>> wants for guest CPUID, and instead cap nr_addr_ranges at
>>>>> min(host.cpuid, guest.cpuid, RTIT_ADDR_RANGE).
>>>
>>> This is the safest option.
I think I misunderstood it. sigh...
It's not architecture consistent that guest sees a certain number of
RTIT_ADDR_RANGE from its CPUID but may get #GP when it accesses high index.
OK, you mean it's userspace's fault and KVM shouldn't get blamed for it.
It seems reasonable for me now.
>> My concern was that change userspace's input silently is not good.
>
> Technically KVM isn't changing userspace's input, as KVM will still enumerate
> CPUID as defined by userspace. What KVM is doing is refusing to emulate/virtualize
> a bogus vCPU model, e.g. by injecting #GP on an MSR access that userspace
> incorrectly told the guest was legal. That is standard operation procedure for
> KVM, e.g. there are any number of instructions that will fault if userspace lies
> about the vCPU model.
>
>> prefer this, we certainly need to extend the userspace to query what value
>> is finally accepted and set by KVM.
>
> That would be __do_cpuid_func()'s responsibility to cap leaf 0x14 output with
> RTIT_ADDR_RANGE. I.e. enumerate the supported ranges in KVM_GET_SUPPORTED_CPUID,
> after that it's userspace's responsibility to not mess up.
>
next prev parent reply other threads:[~2021-10-19 1:46 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 7:02 [PATCH v2 0/7] KVM: VMX: PT (processor trace) optimization cleanup and fixes Xiaoyao Li
2021-08-27 7:02 ` [PATCH v2 1/7] KVM: VMX: Restore host's MSR_IA32_RTIT_CTL when it's not zero Xiaoyao Li
2021-08-27 7:02 ` [PATCH v2 2/7] KVM: VMX: Use precomputed vmx->pt_desc.addr_range Xiaoyao Li
2021-08-27 7:02 ` [PATCH v2 3/7] KVM: VMX: Rename pt_desc.addr_range to pt_desc.nr_addr_range Xiaoyao Li
2021-10-18 12:41 ` Paolo Bonzini
2021-08-27 7:02 ` [PATCH v2 4/7] KVM: VMX: RTIT_CTL_BRANCH_EN has no dependency on other CPUID bit Xiaoyao Li
2021-08-27 7:02 ` [PATCH v2 5/7] KVM: VMX: Disallow PT MSRs accessing if PT is not exposed to guest Xiaoyao Li
2021-10-18 12:46 ` Paolo Bonzini
2021-08-27 7:02 ` [PATCH v2 6/7] KVM: VMX: Check Intel PT related CPUID leaves Xiaoyao Li
2021-09-09 21:41 ` Sean Christopherson
2021-09-10 1:59 ` Xiaoyao Li
2021-10-18 7:01 ` Xiaoyao Li
2021-10-18 12:47 ` Paolo Bonzini
2021-10-18 13:56 ` Xiaoyao Li
2021-10-18 17:26 ` Sean Christopherson
2021-10-19 1:46 ` Xiaoyao Li [this message]
2021-08-27 7:02 ` [PATCH v2 7/7] KVM: VMX: Only context switch some PT MSRs when they exist Xiaoyao Li
2021-10-18 13:08 ` Paolo Bonzini
2021-10-18 14:04 ` Xiaoyao Li
2021-10-18 15:20 ` Paolo Bonzini
2021-10-19 16:52 ` [PATCH v2 0/7] KVM: VMX: PT (processor trace) optimization cleanup and fixes Paolo Bonzini
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