From: Wanpeng Li <kernellwp@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
kvm <kvm@vger.kernel.org>
Subject: Re: [RFC PATCH 4/4] KVM: vmx: add support for emulating UMIP
Date: Tue, 2 Aug 2016 09:05:40 +0800 [thread overview]
Message-ID: <CANRm+Czt2nn3Euj3gxqfCTKt5YdKku6o3DiruuVTXd2Qt1j+KQ@mail.gmail.com> (raw)
In-Reply-To: <a627b86b-162c-ac17-37d9-28a49e3d5fab@redhat.com>
2016-08-01 23:01 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 31/07/2016 04:32, Wanpeng Li wrote:
>> 2016-07-14 16:09 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>> [...]
>>>
>>> This is not necessary because this is how KVM computes
>>> CPUID[EAX=7,EBX=0].ECX:
>>>
>>> unsigned f_umip = kvm_x86_ops->umip_emulated() ? F(UMIP) : 0;
>>> ...
>>> const u32 kvm_cpuid_7_0_ecx_x86_features = F(PKU) | F(UMIP);
>>> ...
>>> // Mask userspace-provided value against supported features
>>> entry->ecx &= kvm_cpuid_7_0_ecx_x86_features;
>>> // Mask userspace-provided value against host features
>>> cpuid_mask(&entry->ecx, CPUID_7_ECX);
>>> // Finally add emulated features
>>> entry->ecx |= f_umip;
>>
>> I think you mean:
>>
>> - entry->ecx -> userspace-provided value
>> - kvm_cpuid_7_0_ecx_x86_features -> supported features
>> - CPUID_7_ECX -> host features
>>
>> However, entry->ecx is returned by cpuid instruction
>> (do_cpuid_1_ent()), so why it is a userspace-provided value?
>
> You're right, it's this:
>
> // Mask host processor value against supported features
> entry->ecx &= kvm_cpuid_7_0_ecx_x86_features;
> // Mask host processor value further, e.g. to drop
> // features that the host kernel has blacklisted.
> cpuid_mask(&entry->ecx, CPUID_7_ECX);
> // Finally add emulated features
> entry->ecx |= f_umip;
>
Cool, more clear this time. :)
> The idea is the same. :)
>
> On the other hand, it is true that in many cases of the "switch
> (function)" the call to do_cpuid_1_ent is unnecessary, and instead of
> cpuid_mask you could just access boot_cpu_data.x86_capability[wordnum].
Agreed.
Regards,
Wanpeng Li
next prev parent reply other threads:[~2016-08-02 6:50 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-12 19:20 [RFC PATCH 0/4] KVM: Emulate UMIP (or almost do so) Paolo Bonzini
2016-07-12 19:20 ` [RFC PATCH 1/4] x86: add UMIP feature and CR4 bit Paolo Bonzini
2016-07-12 19:20 ` [RFC PATCH 2/4] KVM: x86: emulate sldt and str Paolo Bonzini
2016-07-12 19:20 ` [RFC PATCH 3/4] KVM: x86: add support for emulating UMIP Paolo Bonzini
2016-07-13 20:03 ` Radim Krčmář
2016-07-14 7:00 ` Paolo Bonzini
2016-07-14 12:24 ` Radim Krčmář
2016-07-12 19:20 ` [RFC PATCH 4/4] KVM: vmx: " Paolo Bonzini
2016-07-13 9:21 ` Yang Zhang
2016-07-13 9:35 ` Paolo Bonzini
2016-07-13 9:54 ` Yang Zhang
2016-07-13 9:35 ` Paolo Bonzini
2016-07-13 10:02 ` Yang Zhang
2016-07-13 10:21 ` Paolo Bonzini
2016-07-13 20:30 ` Radim Krčmář
2016-07-14 8:09 ` Paolo Bonzini
2016-07-14 12:36 ` Radim Krčmář
2016-07-14 12:54 ` Paolo Bonzini
2016-07-31 2:32 ` Wanpeng Li
2016-08-01 15:01 ` Paolo Bonzini
2016-08-02 1:05 ` Wanpeng Li [this message]
2016-07-13 8:29 ` [RFC PATCH 0/4] KVM: Emulate UMIP (or almost do so) Yang Zhang
2016-07-13 9:34 ` Paolo Bonzini
2016-12-13 4:03 ` Li, Liang Z
2016-12-13 11:03 ` Paolo Bonzini
2017-03-01 9:04 ` Yu Zhang
2017-03-06 21:07 ` Paolo Bonzini
2017-03-10 8:02 ` Yu Zhang
2017-03-10 8:36 ` Paolo Bonzini
2017-03-10 9:31 ` Yu Zhang
2017-03-10 11:28 ` Yu Zhang
2017-03-10 15:00 ` Paolo Bonzini
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