From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien.grall@arm.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
Vijay Kilari <vijay.kilari@gmail.com>,
Andre Przywara <andre.przywara@arm.com>,
Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>,
xen-devel@lists.xenproject.org,
Shanker Donthineni <shankerd@codeaurora.org>
Subject: Re: [PATCH v10 11/32] ARM: GICv3: forward pending LPIs to guests
Date: Wed, 31 May 2017 10:56:41 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1705311054040.18759@sstabellini-ThinkPad-X260> (raw)
In-Reply-To: <dc411b80-7e35-ee24-003f-5bad5bdd9723@arm.com>
On Wed, 31 May 2017, Julien Grall wrote:
> Hi Stefano,
>
> On 30/05/17 23:07, Stefano Stabellini wrote:
> > On Tue, 30 May 2017, Julien Grall wrote:
> > > > };
> > > > };
> > > >
> > > > @@ -136,6 +135,80 @@ uint64_t gicv3_get_redist_address(unsigned int cpu,
> > > > bool use_pta)
> > > > return per_cpu(lpi_redist, cpu).redist_id << 16;
> > > > }
> > > >
> > > > +static void vgic_vcpu_inject_lpi(struct domain *d, unsigned int virq)
> > > > +{
> > > > + struct pending_irq *p = irq_to_pending(d->vcpu[0], virq);
> > > > + struct vcpu *v = NULL;
> > > > +
> > > > + if ( !p )
> > > > + return;
> > > > +
> > > > + if ( p->lpi_vcpu_id < d->max_vcpus )
> > > > + v = d->vcpu[read_atomic(&p->lpi_vcpu_id)];
> > >
> > > Hmmm, what does prevent lpi_vcpu_id to change between the check and the
> > > read?
> >
> > Supposedly we are going to set lpi_vcpu_id only to good values? Meaning
> > that we are going to do the lpi_vcpu_id checks at the time of setting
> > lpi_vcpu_id. Thus, even if lpi_vcpu_id changes, it is not a problem. In
> > fact, if that is true, can we even drop the if ( p->lpi_vcpu_id <
> > d->max_vcpus ) test here?
>
> I am not too confident to say lpi_vcpu_id will always be valid with the
> current locking in the vGIC.
Fair enough, but I wouldn't solve a bug with unnecessary code soon to be
removed. The problem lies elsewhere and should be fixed elsewhere. We
could even add an ASSERT(p->lpi_vcpu_id < d->max_vcpus) here, would
that work for you?
> There is a potential race between its_discard_event and this function. The
> former may reset pending_irq whilst reading lpi_vcpu_id as we cannot take the
> vCPU lock yet.
>
> But all of this is racy anyway because of the locking. This will get solved by
> the vGIC rework after the merge.
>
> So For the time being I would keep the check. We can revisit it later if
> necessary.
This is one of those things that are unimportant because they work
either way.
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next prev parent reply other threads:[~2017-05-31 17:56 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-26 17:35 [PATCH v10 00/32] arm64: Dom0 ITS emulation Andre Przywara
2017-05-26 17:35 ` [PATCH v10 01/32] ARM: vGIC: avoid rank lock when reading priority Andre Przywara
2017-05-30 10:47 ` Julien Grall
2017-05-30 21:39 ` Stefano Stabellini
2017-05-31 10:42 ` Julien Grall
2017-06-02 17:44 ` Julien Grall
2017-06-06 17:06 ` Andre Przywara
2017-06-06 17:11 ` Julien Grall
2017-06-06 17:20 ` Andre Przywara
2017-06-06 17:21 ` Julien Grall
2017-06-06 18:39 ` Stefano Stabellini
2017-05-26 17:35 ` [PATCH v10 02/32] ARM: GICv3: setup number of LPI bits for a GICv3 guest Andre Przywara
2017-05-30 10:54 ` Julien Grall
2017-06-06 10:19 ` Andre Przywara
2017-05-26 17:35 ` [PATCH v10 03/32] ARM: vGIC: move irq_to_pending() calls under the VGIC VCPU lock Andre Przywara
2017-05-30 11:08 ` Julien Grall
2017-05-30 21:46 ` Stefano Stabellini
2017-05-31 10:44 ` Julien Grall
2017-06-06 17:24 ` Andre Przywara
2017-06-06 18:46 ` Stefano Stabellini
2017-06-07 10:49 ` Andre Przywara
2017-05-26 17:35 ` [PATCH v10 04/32] ARM: vGIC: rework gic_remove_from_queues() Andre Przywara
2017-05-30 11:15 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 05/32] ARM: vGIC: introduce gic_remove_irq() Andre Przywara
2017-05-30 11:31 ` Julien Grall
2017-06-06 10:19 ` Andre Przywara
2017-05-26 17:35 ` [PATCH v10 06/32] ARM: GIC: Add checks for NULL pointer pending_irq's Andre Przywara
2017-05-30 11:38 ` Julien Grall
2017-06-06 10:19 ` Andre Przywara
2017-06-07 11:19 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 07/32] ARM: GICv3: introduce separate pending_irq structs for LPIs Andre Przywara
2017-05-26 17:35 ` [PATCH v10 08/32] ARM: GIC: export and extend vgic_init_pending_irq() Andre Przywara
2017-05-26 17:35 ` [PATCH v10 09/32] ARM: vGIC: cache virtual LPI priority in struct pending_irq Andre Przywara
2017-05-26 17:35 ` [PATCH v10 10/32] ARM: vGIC: add LPI VCPU ID to " Andre Przywara
2017-05-26 17:35 ` [PATCH v10 11/32] ARM: GICv3: forward pending LPIs to guests Andre Przywara
2017-05-30 11:56 ` Julien Grall
2017-05-30 22:07 ` Stefano Stabellini
2017-05-31 11:09 ` Julien Grall
2017-05-31 17:56 ` Stefano Stabellini [this message]
2017-05-31 18:39 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 12/32] ARM: GICv3: enable ITS and LPIs on the host Andre Przywara
2017-05-30 11:58 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 13/32] ARM: vGICv3: handle virtual LPI pending and property tables Andre Przywara
2017-05-26 17:35 ` [PATCH v10 14/32] ARM: introduce vgic_access_guest_memory() Andre Przywara
2017-05-26 17:35 ` [PATCH v10 15/32] ARM: vGICv3: re-use vgic_reg64_check_access Andre Przywara
2017-05-26 17:35 ` [PATCH v10 16/32] ARM: vGIC: advertise LPI support Andre Przywara
2017-05-30 12:59 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 17/32] ARM: vITS: add command handling stub and MMIO emulation Andre Przywara
2017-06-01 18:13 ` Julien Grall
2017-06-08 9:57 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 18/32] ARM: vITS: introduce translation table walks Andre Przywara
2017-06-02 16:25 ` Julien Grall
2017-06-08 9:35 ` Julien Grall
2017-06-08 9:45 ` Andre Przywara
2017-05-26 17:35 ` [PATCH v10 19/32] ARM: vITS: provide access to struct pending_irq Andre Przywara
2017-06-02 16:32 ` Julien Grall
2017-06-02 16:45 ` Julien Grall
2017-06-06 10:19 ` Andre Przywara
2017-06-06 11:13 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 20/32] ARM: vITS: handle INT command Andre Przywara
2017-06-02 16:37 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 21/32] ARM: vITS: handle MAPC command Andre Przywara
2017-05-26 17:35 ` [PATCH v10 22/32] ARM: vITS: handle CLEAR command Andre Przywara
2017-06-02 16:40 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 23/32] ARM: vITS: handle MAPD command Andre Przywara
2017-06-02 16:46 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 24/32] ARM: GICv3: handle unmapped LPIs Andre Przywara
2017-06-02 16:55 ` Julien Grall
2017-06-02 20:45 ` Stefano Stabellini
2017-06-08 9:45 ` Julien Grall
2017-06-08 13:51 ` Andre Przywara
2017-05-26 17:35 ` [PATCH v10 25/32] ARM: vITS: handle MAPTI/MAPI command Andre Przywara
2017-06-02 17:12 ` Julien Grall
2017-06-07 17:49 ` Andre Przywara
2017-06-12 16:33 ` Julien Grall
2017-06-09 11:17 ` Andre Przywara
2017-06-09 19:14 ` Stefano Stabellini
2017-06-12 16:10 ` Andre Przywara
2017-05-26 17:35 ` [PATCH v10 26/32] ARM: vITS: handle MOVI command Andre Przywara
2017-05-30 22:35 ` Stefano Stabellini
2017-05-31 11:23 ` Julien Grall
2017-05-31 17:53 ` Stefano Stabellini
2017-05-31 18:49 ` Julien Grall
2017-06-02 17:17 ` Julien Grall
2017-06-02 20:36 ` Stefano Stabellini
2017-05-26 17:35 ` [PATCH v10 27/32] ARM: vITS: handle DISCARD command Andre Przywara
2017-06-02 17:21 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 28/32] ARM: vITS: handle INV command Andre Przywara
2017-05-30 22:23 ` Stefano Stabellini
2017-05-26 17:35 ` [PATCH v10 29/32] ARM: vITS: handle INVALL command Andre Przywara
2017-06-02 17:27 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 30/32] ARM: vITS: increase mmio_count for each ITS Andre Przywara
2017-05-26 17:35 ` [PATCH v10 31/32] ARM: vITS: create and initialize virtual ITSes for Dom0 Andre Przywara
2017-06-02 17:31 ` Julien Grall
2017-05-26 17:35 ` [PATCH v10 32/32] ARM: vITS: create ITS subnodes for Dom0 DT Andre Przywara
2017-06-02 17:33 ` Julien Grall
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