linux-kernel - Re: [PATCH 0/6] KVM: x86: KVM_SET

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Date:   Thu, 8 Oct 2020 21:18:18 +0300
From:   stsp <stsp2@...dex.ru>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] KVM: x86: KVM_SET_SREGS.CR4 bug fixes and cleanup

08.10.2020 20:59, Sean Christopherson пишет:
> On Thu, Oct 08, 2020 at 07:00:13PM +0300, stsp wrote:
>> 07.10.2020 04:44, Sean Christopherson пишет:
>>> Two bug fixes to handle KVM_SET_SREGS without a preceding KVM_SET_CPUID2.
>> Hi Sean & KVM devs.
>>
>> I tested the patches, and wherever I
>> set VMXE in CR4, I now get
>> KVM: KVM_SET_SREGS: Invalid argument
>> Before the patch I was able (with many
>> problems, but still) to set VMXE sometimes.
>>
>> So its a NAK so far, waiting for an update. :)
> IIRC, you said you were going to test on AMD?  Assuming that's correct,

Yes, that is true.


>   -EINVAL
> is the expected behavior.  KVM was essentially lying before; it never actually
> set CR4.VMXE in hardware, it just didn't properply detect the error and so VMXE
> was set in KVM's shadow of the guest's CR4.

Hmm. But at least it was lying
similarly on AMD and Intel CPUs. :)
So I was able to reproduce the problems
myself.
Do you mean, any AMD tests are now
useless, and we need to proceed with
Intel tests only?

Then additional question.
On old Intel CPUs we needed to set
VMXE in guest to make it to work in
nested-guest mode.
Is it still needed even with your patches?
Or the nested-guest mode will work
now even on older Intel CPUs and KVM
will set VMXE for us itself, when needed?