linux-kernel - Re: [PATCH 1/2] xen/x2apic: enable x2apic mode when supported

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Date:   Thu, 20 Jan 2022 20:01:57 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Roger Pau Monne <roger.pau@...rix.com>,
        linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 1/2] xen/x2apic: enable x2apic mode when supported



On 1/20/22 10:25 AM, Roger Pau Monne wrote:
> There's no point in disabling x2APIC mode when running as a Xen HVM
> guest, just enable it when available.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Stefano Stabellini <sstabellini@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: x86@...nel.org
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: xen-devel@...ts.xenproject.org
> ---
>   arch/x86/xen/enlighten_hvm.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index 42300941ec29..ab8171cbee23 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -9,6 +9,7 @@
>   #include <xen/events.h>
>   #include <xen/interface/memory.h>
>   
> +#include <asm/apic.h>
>   #include <asm/cpu.h>
>   #include <asm/smp.h>
>   #include <asm/io_apic.h>
> @@ -248,7 +249,7 @@ bool __init xen_hvm_need_lapic(void)
>   		return false;
>   	if (!xen_hvm_domain())
>   		return false;
> -	if (xen_feature(XENFEAT_hvm_pirqs) && xen_have_vector_callback)
> +	if (!x2apic_supported())
>   		return false;
>   	return true;
>   }


Then it seems this whole routine can be reduced to just

	return x2apic_supported();

and then dropped altogether and x2apic_supported() moved to xen_x2apic_para_available(). Domain type checks here are not really needed since this can only be called on HVM guests.


-boris