linux-kernel - Re: [PATCH] xen/pv: Add PV specific legacy

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Date:   Thu, 21 Mar 2019 17:49:43 +0000
From:   Jennifer Herbert <Jennifer.Herbert@...rix.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>, <x86@...nel.org>,
        <xen-devel@...ts.xenproject.org>, <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>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] xen/pv: Add PV specific legacy_pic struct to expose
 legacy IRQs.



On 19/03/19 23:06, Boris Ostrovsky wrote:
> On 3/19/19 4:02 PM, Jennifer Herbert wrote:
>> The ACPI tables doesn't always contain all IRQs for legacy devices
>> such as RTC.  Since no PIC controller is visible for a PV linux guest,
>> under Xen, legacy_pic currently defaults to the null_legacy_pic - with
>> reports no legacy IRQs.  Since the commit "rtc: cmos: Do not assume
>> irq 8 for rtc when there are no legacy irqs" by Hans de Goede
>> (commit id: a1e23a42f1bdc00e32fc4869caef12e4e6272f26), the rtc now
>> incorrectly decides it has no irq it can use, for some hardware.
>>
>> This patch rectifies the problem by providing a xen legacy_pic
>> struct, which is much like the null_legacy_pic except that it
>> reports NR_IRQS_LEGACY irqs.
> I assume this is for dom0?
>
> Could there be the same problem with PVH dom0? (and if yes then this
> should probably go into arch/x86/xen/enlighten.c).
>
> -boris
>

I am doing this to fix a problem with dom0.  DomU doesn't seem to have 
an RTC, and so it is unaffected.

I'm not familiar with PVH, but have now done some experiments.  The RTC 
on PVH seems broken - but not quite in the same way as PV. More research 
is needed, however simply doing the same trick I did with PV will not 
fix the issue.

I'll look further into it.

Cheer,

-jenny