linux-kernel - Re: [PATCH v2 4/6] KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET

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Message-ID: <05161b6e-6d85-be14-9e30-e61cb742f6d0@redhat.com>
Date:   Mon, 26 Apr 2021 15:28:40 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH v2 4/6] KVM: x86: Introduce KVM_GET_SREGS2 /
 KVM_SET_SREGS2

On 26/04/21 14:56, Maxim Levitsky wrote:
> On Mon, 2021-04-26 at 14:32 +0200, Paolo Bonzini wrote:
>> On 26/04/21 13:13, Maxim Levitsky wrote:
>>> +	if (sregs2->flags & KVM_SREGS2_FLAGS_PDPTRS_VALID) {
>>> +
>>> +		if (!is_pae_paging(vcpu))
>>> +			return -EINVAL;
>>> +
>>> +		for (i = 0 ; i < 4 ; i++)
>>> +			kvm_pdptr_write(vcpu, i, sregs2->pdptrs[i]);
>>> +
>>> +		kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
>>> +		mmu_reset_needed = 1;
>>> +	}
>>
>> I think this should also have
>>
>> 	else {
>> 		if (is_pae_paging(vcpu))
>> 			return -EINVAL;
>> 	}
> 
> 
> What about the case when we migrate from qemu that doesn't use
> this ioctl to qemu that does?

Right, that makes sense but then the "else" branch should do the same as 
KVM_SET_SREGS.  Maybe add a "load_pdptrs" bool to __set_sregs_common?

Paolo