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

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Date:   Mon, 05 Feb 2018 22:26:44 +0000
From:   Jim Mattson <jmattson@...gle.com>
To:     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 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.

> @@ -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?