From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
<xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v3 06/11] x86/hvm: allowing registering EOI callbacks for GSIs
Date: Mon, 19 Apr 2021 10:31:26 +0200 [thread overview]
Message-ID: <YH0/3v6WKEQOQoay@Air-de-Roger> (raw)
In-Reply-To: <afb9ad03-d946-55c3-5f51-62683b69f0dc@suse.com>
On Fri, Apr 16, 2021 at 09:29:26AM +0200, Jan Beulich wrote:
> On 15.04.2021 18:04, Roger Pau Monné wrote:
> > On Wed, Apr 07, 2021 at 07:08:06PM +0200, Roger Pau Monné wrote:
> >> On Wed, Apr 07, 2021 at 05:51:14PM +0200, Jan Beulich wrote:
> >>> On 31.03.2021 12:32, Roger Pau Monne wrote:
> >>>> --- a/xen/arch/x86/hvm/irq.c
> >>>> +++ b/xen/arch/x86/hvm/irq.c
> >>>> +void hvm_gsi_execute_callbacks(unsigned int gsi)
> >>>> +{
> >>>> + struct hvm_irq *hvm_irq = hvm_domain_irq(current->domain);
> >>>> + struct hvm_gsi_eoi_callback *cb;
> >>>> +
> >>>> + read_lock(&hvm_irq->gsi_callbacks_lock);
> >>>> + list_for_each_entry ( cb, &hvm_irq->gsi_callbacks[gsi], list )
> >>>> + cb->callback(gsi, cb->data);
> >>>> + read_unlock(&hvm_irq->gsi_callbacks_lock);
> >>>> +}
> >>>
> >>> Just as an observation (for now at least) - holding the lock here
> >>> means the callbacks cannot re-register themselves.
> >>
> >> Well, re-registering would be weird, as the callback is not
> >> unregistered after execution. What is likely more relevant is that the
> >> callback cannot unregister itself. I haven't found a need for this so
> >> far, so I think it's fine.
> >
> > I'm afraid I was wrong here - rtc_pf_callback could attempt to
> > unregister the timer, and thus end up calling
> > hvm_gsi_unregister_callback inside of a callback.
> >
> > I need to figure a way to solve this. We already run the RTC in no ack
> > mode (which is correct because of the flag we expose in the WAET ACPI
> > table), and hence I wonder if we still need to keep the code for the
> > strict_mode around, since it's not used at all. Would you be OK with
> > me removing the mode_strict related code?
>
> Not sure, to be honest. Years ago I did submit a patch correcting this
> ("x86/HVM: tie RTC emulation mode to enabling of Viridian emulation"),
> as we shouldn't assume all guests to even know of WAET.
It's very likely guest that don't even know about WAET to continue
working fine even in the no_ack mode. In fact the current code for
strict_mode will inject 10 interrupts without REG_C being read, as
there's no check for the value of REG_C before injecting the
interrupt.
> Hence running
> uniformly in rtc_mode_no_ack isn't really correct. I'm still carrying
> this patch, as Tim (iirc) had asked not to tie the behavior to the
> Viridian param, but give it its own one. Which I still didn't get to.
>
> Of course, if we decided to drop mode_strict support, I could also
> drop that patch ...
AFAICT the no_ack mode it's been used since Xen 4.3, and so far we had
no complains, so I think it's safe to just remove the code for
strict_mode. It can always be fetched from the repository history if
there's a need to support strict_mode in the future.
Thanks, Roger.
next prev parent reply other threads:[~2021-04-19 8:31 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-31 10:32 [PATCH v3 00/11] x86/intr: introduce EOI callbacks and fix vPT Roger Pau Monne
2021-03-31 10:32 ` [PATCH v3 01/11] x86/hvm: drop vcpu parameter from vlapic EOI callbacks Roger Pau Monne
2021-03-31 16:02 ` Jan Beulich
2021-03-31 16:24 ` Andrew Cooper
2021-04-01 9:12 ` Roger Pau Monné
2021-04-01 11:06 ` Jan Beulich
2021-04-07 7:41 ` Roger Pau Monné
2021-04-07 8:19 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 02/11] x86/hvm: drop domain parameter from vioapic/vpic " Roger Pau Monne
2021-03-31 16:04 ` Jan Beulich
2021-04-01 9:15 ` Roger Pau Monné
2021-04-01 9:28 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 03/11] x86/vlapic: introduce an EOI callback mechanism Roger Pau Monne
2021-03-31 11:47 ` Andrew Cooper
2021-03-31 12:50 ` Roger Pau Monné
2021-04-07 14:55 ` Jan Beulich
2021-04-07 16:27 ` Roger Pau Monné
2021-04-08 6:20 ` Jan Beulich
2021-04-08 9:12 ` Roger Pau Monné
2021-04-08 10:49 ` Jan Beulich
2021-04-08 10:56 ` Roger Pau Monné
2021-03-31 10:32 ` [PATCH v3 04/11] x86/vmsi: use the newly introduced EOI callbacks Roger Pau Monne
2021-04-07 14:59 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 05/11] x86/vioapic: switch to use the EOI callback mechanism Roger Pau Monne
2021-04-07 15:19 ` Jan Beulich
2021-04-07 16:46 ` Roger Pau Monné
2021-04-08 6:27 ` Jan Beulich
2021-04-08 8:59 ` Roger Pau Monné
2021-04-08 10:52 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 06/11] x86/hvm: allowing registering EOI callbacks for GSIs Roger Pau Monne
2021-04-07 15:51 ` Jan Beulich
2021-04-07 17:08 ` Roger Pau Monné
2021-04-08 6:34 ` Jan Beulich
2021-04-15 16:04 ` Roger Pau Monné
2021-04-16 7:29 ` Jan Beulich
2021-04-19 8:31 ` Roger Pau Monné [this message]
2021-04-08 12:52 ` Roger Pau Monné
2021-04-08 14:31 ` Jan Beulich
2021-04-08 15:06 ` Roger Pau Monné
2021-03-31 10:32 ` [PATCH v3 07/11] x86/dpci: move code Roger Pau Monne
2021-03-31 10:33 ` [PATCH v3 08/11] x86/dpci: switch to use a GSI EOI callback Roger Pau Monne
2021-04-08 14:49 ` Jan Beulich
2021-04-08 15:23 ` Roger Pau Monné
2021-03-31 10:33 ` [PATCH v3 09/11] x86/vpt: switch interrupt injection model Roger Pau Monne
2021-04-14 10:28 ` Jan Beulich
2021-04-14 13:37 ` Roger Pau Monné
2021-04-14 14:05 ` Jan Beulich
2021-04-14 14:20 ` Roger Pau Monné
2021-03-31 10:33 ` [PATCH v3 10/11] x86/vpt: remove vPT timers per-vCPU lists Roger Pau Monne
2021-04-14 10:38 ` Jan Beulich
2021-03-31 10:33 ` [PATCH v3 11/11] x86/vpt: introduce a per-vPT lock Roger Pau Monne
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