linux-kernel - Re: [PATCH v2 5/9] xen/pvh: Prevent PVH guests from using PIC, RTC and IOAPIC

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Date:   Thu, 2 Feb 2017 15:35:15 +0000
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:     <JGross@...e.com>, <xen-devel@...ts.xenproject.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/9] xen/pvh: Prevent PVH guests from using PIC, RTC
 and IOAPIC

On Thu, Jan 26, 2017 at 02:41:28PM -0500, Boris Ostrovsky wrote:
> Make sure they don't use these devices since they are not emulated
> for unprivileged PVH guest.

This description seems weird for what it's actually done. AFAICT you are not
really preventing the guest from using the PIC or the IO APIC, because this is
fetched from the MADT table (or should be fetched from there in any case).

See below for the RTC...

[...]
> @@ -1892,6 +1900,9 @@ static void __init xen_hvm_guest_init(void)
>  
>  	init_hvm_pv_info();
>  
> +	if (xen_pvh_domain())
> +		x86_platform.legacy.rtc = 0;

Can't you fetch that from the FADT boot flags field? (See "5.2.9.3 IA-PC Boot
Architecture Flags" in ACPI 6.1 spec).

Roger.