Re: [PATCH v2 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jane Malalane <Jane.Malalane@citrix.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>, Wei Liu <wl@xen.org>,
	Anthony Perard <anthony.perard@citrix.com>,
	Juergen Gross <jgross@suse.com>,
	Andrew Cooper <Andrew.Cooper3@citrix.com>,
	George Dunlap <George.Dunlap@citrix.com>,
	Jan Beulich <jbeulich@suse.com>, Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Christian Lindig <christian.lindig@citrix.com>,
	David Scott <dave@recoil.org>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [PATCH v2 2/2] x86/xen: Allow per-domain usage of hardware virtualized APIC
Date: Thu, 10 Feb 2022 10:37:22 +0100	[thread overview]
Message-ID: <YgTc0sgui8f80LTS@Air-de-Roger> (raw)
In-Reply-To: <76de6f28-f038-7e8f-ce3c-a3686112b1d4@citrix.com>

On Wed, Feb 09, 2022 at 10:57:28AM +0000, Jane Malalane wrote:
> On 08/02/2022 16:17, Roger Pau Monné wrote:
> > On Mon, Feb 07, 2022 at 06:21:01PM +0000, Jane Malalane wrote:
> >> diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
> >> index 485bd66971..33694acc99 100644
> >> --- a/xen/arch/x86/traps.c
> >> +++ b/xen/arch/x86/traps.c
> >> @@ -1115,7 +1115,8 @@ void cpuid_hypervisor_leaves(const struct vcpu *v, uint32_t leaf,
> >>           if ( !is_hvm_domain(d) || subleaf != 0 )
> >>               break;
> >>   
> >> -        if ( cpu_has_vmx_apic_reg_virt )
> >> +        if ( cpu_has_vmx_apic_reg_virt &&
> > 
> > You can drop the cpu_has_vmx_apic_reg_virt check here, if
> > cpu_has_vmx_apic_reg_virt is false assisted_xapic won't be set to true.
> Oh, but assisted_xapic_available is only set to depend on 
> cpu_has_vmx_virtualize_apic_accesses, unless I should correct this, but 
>   I might be missing something...

No, you are right. We only report hw virtualized xAPIC to guests if
both apic_reg_virt and virtualize_apic_accesses are available.

Thanks, Roger.