linux-kernel - Re: [PATCH 5/8] xen/pvh: Prevent PVH guests from using PIC, RTC and IOAPIC

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Message-ID: <16d3a435-25c2-33b6-27a8-713dd9e54b7e@oracle.com>
Date:   Wed, 26 Oct 2016 10:50:21 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Roger Pau Monné <roger.pau@...rix.com>
Cc:     david.vrabel@...rix.com, JGross@...e.com,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 5/8] xen/pvh: Prevent PVH guests from using PIC, RTC and
 IOAPIC

On 10/26/2016 06:42 AM, Roger Pau Monné wrote:
> On Fri, Oct 14, 2016 at 02:05:15PM -0400, Boris Ostrovsky wrote:
>> Make sure they don't use these devices since they are not emulated
>> for unprivileged PVH guest.
>>
>> Also don't initialize hypercall page for them in init_hvm_pv_info()
>> since this has already been done.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> ---
>>  arch/x86/xen/enlighten.c | 24 +++++++++++++++++-------
>>  1 file changed, 17 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
>> index d38d568..6c1a330 100644
>> --- a/arch/x86/xen/enlighten.c
>> +++ b/arch/x86/xen/enlighten.c
>> @@ -1803,10 +1803,21 @@ static void __init init_hvm_pv_info(void)
>>  	minor = eax & 0xffff;
>>  	printk(KERN_INFO "Xen version %d.%d.\n", major, minor);
>>  
>> -	cpuid(base + 2, &pages, &msr, &ecx, &edx);
>> +	xen_domain_type = XEN_HVM_DOMAIN;
>>  
>> -	pfn = __pa(hypercall_page);
>> -	wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
>> +	/* PVH set up hypercall page earlier in xen_prepare_pvh() */
>> +	if (xen_pvh_domain()) {
>> +		pv_info.name = "Xen PVH";
>> +#ifdef CONFIG_ACPI
>> +		/* No PIC or IOAPIC */
> Shouldn't this be fetched from the MADT ACPI table if ACPI is available 
> (rsdp_paddr != 0 in start_info)?


At this point we haven't parsed ACPI yet (with or without rsdp_paddr,
which we don't set anyway for domU) so we don't know whether we have PIC
or IOAPIC.

Having said that, I will probably remove this ("acpi_irq_model =
ACPI_IRQ_MODEL_PLATFORM", together with the comment) since I am working
on adding SCI support via an event channel and ACPI_IRQ_MODEL_PIC model,
which is default, seems to work OK.

Alternatively, I may keep ACPI_IRQ_MODEL_PLATFORM but then I'd need to
make changes to acpi_gsi_to_irq().

-boris