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

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Date:   Wed, 26 Oct 2016 12:06:31 -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 11:18 AM, Roger Pau Monné wrote:
> On Wed, Oct 26, 2016 at 10:50:21AM -0400, Boris Ostrovsky wrote:
>> 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.
> I guess I'm missing something, but if we are providing ACPI tables to a PVH
> DomU rsdp_paddr should be set, or else we are failing to comply with our own
> start info specification.

acpi_find_root_pointer() searches low MB of memory for the RSDP
signature. This is standard ACPICA's method of finding it, I'd think
that FreeBSD does the same thing. And that's how a non-UEFI system is
expected to find it as required by the ACPI spec ("Root System
Description Pointer (RSDP)" section)

RSDP structure is placed at RSDP_ADDRESS (which is just under 1MB at
0xfffc0) by libxl__dom_load_acpi().


>  
>> 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.
> Hm, right, that might be an option.

I'd actually prefer not to use ACPI_IRQ_MODEL_PIC since it implies that
we have a PIC (which we don't). It just so happens that using it in
Linux works for PVH as well.

>  Do you know how hardware-reduced ACPI 
> implementations (which IIRC also don't have a SCI interrupt) deliver events 
> to the OS? Or it's simply not possible in that case?

I believe you need _AEI object for that. At least that's what section
"4.1.1.1 GPIO-Signaled Events" suggests.


-boris