From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v7 13/32] xen/vlapic: fixes for HVM code
 when running without a vlapic
Date: Fri, 2 Oct 2015 19:23:35 +0100
Message-ID: <560ECBA7.306@citrix.com>
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To: Roger Pau Monne <roger.pau@citrix.com>, xen-devel@lists.xenproject.org
Cc: Kevin Tian <kevin.tian@intel.com>, Jan Beulich <jbeulich@suse.com>, Eddie Dong <eddie.dong@intel.com>, Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>, Jun Nakajima <jun.nakajima@intel.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
List-Id: xen-devel@lists.xenproject.org

On 02/10/15 16:48, Roger Pau Monne wrote:
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index bbec0e8..63b7a24 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -2412,7 +2412,8 @@ static void vmx_install_vlapic_mapping(struct vcpu *v)
>  {
>      paddr_t virt_page_ma, apic_page_ma;
>  
> -    if ( !cpu_has_vmx_virtualize_apic_accesses )
> +    if ( !cpu_has_vmx_virtualize_apic_accesses ||
> +         v->domain->arch.hvm_domain.vmx.apic_access_mfn == 0 )

0 is a valid (albeit very unlikely) mfn.  The unused sentinel value
should be INVALID_MFN.  It appears that all the current uses of
apic_access_mfn are buggy.