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Date: Thu, 6 Jun 2019 09:30:46 +0800
From: Like Xu <like.xu@...ux.intel.com>
To: Sean Christopherson <sean.j.christopherson@...el.com>,
Radim Krčmář <rkrcmar@...hat.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v3] KVM: x86: Add Intel CPUID.1F cpuid emulation
support
On 2019/6/4 3:18, Sean Christopherson wrote:
> On Mon, Jun 03, 2019 at 06:56:17PM +0200, Radim Krčmář wrote:
>>> + break;
>>> + }
>>> entry->eax = min(entry->eax, (u32)(f_intel_pt ? 0x14 : 0xd));
>>
>> Similarly in the existing code. If we don't have f_intel_pt, then we
>> should make sure that leaf 0x14 is not being filled, but we don't really
>> have to limit the maximal index.
>>
>> Adding a single clamping like
>>
>> /* Limited to the highest leaf implemented in KVM. */
>> entry->eax = min(entry->eax, 0x1f);
>>
>> seems sufficient.
>>
>> (Passing the hardware value is ok in theory, but it is a cheap way to
>> avoid future leaves that cannot be simply zeroed for some weird reason.)
>
> I don't have a strong opinion regarding the code itself, but whatever ends
> up getting committed should have a big beefy changelog explaining why the
> clamping exists, or at least extolling its virtues. I had a hell of a
> time understanding the intent of this one line of code because as your
> response shows, there is no one right answer.
>
Hi Radim & Sean,
Thanks for your review and finally we find a better way.
Please help review the new version, I am not sure that the changelog
could help new submitter understand why the clamping exists.
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