linux-kernel - Re: [RFC 05/12] KVM/VMX: Use the new host mapping API for mapping nested vmptr

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Message-ID: <ad1fd6bd-0dd3-52c0-0343-dc9f0cb4f5f8@amazon.com>
Date:   Thu, 8 Feb 2018 19:51:39 +0100
From:   KarimAllah Ahmed <karahmed@...zon.com>
To:     Jim Mattson <jmattson@...gle.com>,
        KarimAllah Ahmed <karahmed@...zon.de>
CC:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [RFC 05/12] KVM/VMX: Use the new host mapping API for mapping
 nested vmptr

On 02/05/2018 11:15 PM, Jim Mattson wrote:
> On Mon, Feb 5, 2018 at 10:49 AM KarimAllah Ahmed <karahmed@...zon.de> wrote:
> 
> 
>> @@ -7410,19 +7410,17 @@ static int handle_vmon(struct kvm_vcpu *vcpu)
>>                   return kvm_skip_emulated_instruction(vcpu);
>>           }
> 
>> -       page = kvm_vcpu_gpa_to_page(vcpu, vmptr);
>> -       if (is_error_page(page)) {
>> +       if (!kvm_vcpu_gpa_to_host_mapping(vcpu, vmptr, &mapping, true)) {
>>                   nested_vmx_failInvalid(vcpu);
>>                   return kvm_skip_emulated_instruction(vcpu);
>>           }
>> -       if (*(u32 *)kmap(page) != VMCS12_REVISION) {
>> -               kunmap(page);
>> -               kvm_release_page_clean(page);
>> +       if (*(u32 *)mapping.kaddr != VMCS12_REVISION) {
>> +               kvm_release_host_mapping(&mapping, false);
>>                   nested_vmx_failInvalid(vcpu);
>>                   return kvm_skip_emulated_instruction(vcpu);
>>           }
>> -       kunmap(page);
>> -       kvm_release_page_clean(page);
>> +
>> +       kvm_release_host_mapping(&mapping, false);
> 
> Why go through this explicit mapping/release dance? Why not just:
> 
> uint32_t revision;
> ...
> if (kvm_read_guest(vcpu->kvm, vmptr, &revision, sizeof(revision)) ||
>       revision != VMCS12_REVISION) {
>           nested_vmx_failInvalid(vcpu);
>           return kvm_skip_emulated_instruction(vcpu);
> }
> 

Fair enough, I will update.
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