linux-kernel - Re: [RFC 03/12] KVM/VMX: Use the new host mapping API for virtual_apic

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Message-ID: <b12b9a53-2793-5317-bc59-535b615eb903@amazon.com>
Date:   Fri, 9 Feb 2018 13:15:18 +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 03/12] KVM/VMX: Use the new host mapping API for
 virtual_apic_page

On 02/05/2018 11:26 PM, Jim Mattson wrote:
> On Mon, Feb 5, 2018 at 10:48 AM KarimAllah Ahmed <karahmed@...zon.de> wrote:
> 
>> @@ -5264,9 +5264,8 @@ static void
> vmx_complete_nested_posted_interrupt(struct kvm_vcpu *vcpu)
> 
>>           max_irr = find_last_bit((unsigned long
> *)vmx->nested.pi_desc->pir, 256);
>>           if (max_irr != 256) {
>> -               vapic_page = kmap(vmx->nested.virtual_apic_page);
>> +               vapic_page = vmx->nested.virtual_apic_mapping.kaddr;
>>                   __kvm_apic_update_irr(vmx->nested.pi_desc->pir,
> vapic_page);
>> -               kunmap(vmx->nested.virtual_apic_page);
> 
> Your kernel mapping now survives exits to userspace. I didn't think that
> was kosher, but I'd be happy to hear that I'm wrong.

Can you elaborate a bit? I do not really understand what is the concern.

>> @@ -7502,10 +7501,8 @@ static void free_nested(struct vcpu_vmx *vmx)
>>           /* Unpin physical memory we referred to in the vmcs02 */
>>           if (vmx->nested.apic_access_mapping.pfn)
> 
> kvm_release_host_mapping(&vmx->nested.apic_access_mapping, true);
>> -       if (vmx->nested.virtual_apic_page) {
>> -               kvm_release_page_dirty(vmx->nested.virtual_apic_page);
>> -               vmx->nested.virtual_apic_page = NULL;
>> -       }
>> +       if (vmx->nested.virtual_apic_mapping.pfn)
>> +
> kvm_release_host_mapping(&vmx->nested.virtual_apic_mapping, true);
> 
> Is the host PFN guaranteed to be non-zero?

Yeah, I should not have assumed that PFN zero is invalid. Will fix.
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