From: luojiaxing <luojiaxing@huawei.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Shenming Lu <lushenming@huawei.com>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Eric Auger <eric.auger@redhat.com>,
<linux-arm-kernel@lists.infradead.org>,
<kvmarm@lists.cs.columbia.edu>, <kvm@vger.kernel.org>,
<linux-kernel@vger.kernel.org>,
Christoffer Dall <christoffer.dall@arm.com>,
Alex Williamson <alex.williamson@redhat.com>,
Kirti Wankhede <kwankhede@nvidia.com>,
Cornelia Huck <cohuck@redhat.com>, "Neo Jia" <cjia@nvidia.com>,
<wanghaibin.wang@huawei.com>, <yuzenghui@huawei.com>
Subject: Re: [RFC PATCH v1 1/4] irqchip/gic-v4.1: Plumb get_irqchip_state VLPI callback
Date: Tue, 1 Dec 2020 17:38:12 +0800 [thread overview]
Message-ID: <316fe41d-f004-f004-4f31-6fe6e7ff64b7@huawei.com> (raw)
In-Reply-To: <875z5p6ayp.wl-maz@kernel.org>
On 2020/11/28 18:18, Marc Zyngier wrote:
> On Sat, 28 Nov 2020 07:19:48 +0000,
> luojiaxing <luojiaxing@huawei.com> wrote:
>> Hi, shenming
>>
>>
>> I got few questions about this patch.
>>
>> Although it's a bit late and not very appropriate, I'd like to ask
>> before you send next version.
>>
>> On 2020/11/23 14:54, Shenming Lu wrote:
>>> From: Zenghui Yu <yuzenghui@huawei.com>
>>>
>>> Up to now, the irq_get_irqchip_state() callback of its_irq_chip
>>> leaves unimplemented since there is no architectural way to get
>>> the VLPI's pending state before GICv4.1. Yeah, there has one in
>>> v4.1 for VLPIs.
>>
>> I checked the invoking scenario of irq_get_irqchip_state and found no
>> scenario related to vLPI.
>>
>> For example, synchronize_irq(), it pass IRQCHIP_STATE_ACTIVE to which,
>> so in your patch, you will directly return and other is for vSGI,
>> GICD_ISPENDR, GICD_ICPENDR and so on.
> You do realise that LPIs have no active state, right?
yes, I know
> And that LPIs
> have a radically different programming interface to the rest of the GIC?
I found out that my mailbox software filtered out the other two patches,
which led me to look at the patch alone, so it was weird. I already got
the answer now.
>> The only one I am not sure is vgic_get_phys_line_level(), is it your
>> purpose to fill this callback, or some scenarios I don't know about
>> that use this callback.
> LPIs only offer edge signalling, so the concept of "line level" means
> absolutely nothing.
>
>>
>>> With GICv4.1, after unmapping the vPE, which cleans and invalidates
>>> any caching of the VPT, we can get the VLPI's pending state by
>>> peeking at the VPT. So we implement the irq_get_irqchip_state()
>>> callback of its_irq_chip to do it.
>>>
>>> Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
>>> Signed-off-by: Shenming Lu <lushenming@huawei.com>
>>> ---
>>> drivers/irqchip/irq-gic-v3-its.c | 38 ++++++++++++++++++++++++++++++++
>>> 1 file changed, 38 insertions(+)
>>>
>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>>> index 0fec31931e11..287003cacac7 100644
>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>> @@ -1695,6 +1695,43 @@ static void its_irq_compose_msi_msg(struct irq_data *d, struct msi_msg *msg)
>>> iommu_dma_compose_msi_msg(irq_data_get_msi_desc(d), msg);
>>> }
>>> +static bool its_peek_vpt(struct its_vpe *vpe, irq_hw_number_t
>>> hwirq)
>>> +{
>>> + int mask = hwirq % BITS_PER_BYTE;
>>> + void *va;
>>> + u8 *pt;
>>> +
>>> + va = page_address(vpe->vpt_page);
>>> + pt = va + hwirq / BITS_PER_BYTE;
>>> +
>>> + return !!(*pt & (1U << mask));
>>
>> How can you confirm that the interrupt pending status is the latest?
>> Is it possible that the interrupt pending status is still cached in
>> the GICR but not synchronized to the memory.
> That's a consequence of the vPE having been unmapped:
>
> "A VMAPP with {V,Alloc}=={0,1} cleans and invalidates any caching of
> the Virtual Pending Table and Virtual Configuration Table associated
> with the vPEID held in the GIC."
Yes, in addition to that, if a vPE is scheduled out of the PE, the cache
clearing and write-back to VPT are also performed, I think.
However, I feel a litter confusing to read this comment at first ,
because it is not only VMAPP that causes cache clearing.
I don't know why VMAPP was mentioned here until I check the other two
patches ("KVM: arm64: GICv4.1: Try to save hw pending state in
save_pending_tables").
So I think may be it's better to add some background description here.
Thanks
Jiaxing
>
> An implementation that wouldn't follow this simple rule would simply
> be totally broken, and unsupported.
>
> M.
>
next prev parent reply other threads:[~2020-12-01 9:39 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-23 6:54 [RFC PATCH v1 0/4] KVM: arm64: Add VLPI migration support on GICv4.1 Shenming Lu
2020-11-23 6:54 ` [RFC PATCH v1 1/4] irqchip/gic-v4.1: Plumb get_irqchip_state VLPI callback Shenming Lu
2020-11-23 9:01 ` Marc Zyngier
2020-11-24 7:38 ` Shenming Lu
2020-11-24 8:08 ` Marc Zyngier
2020-11-28 7:19 ` luojiaxing
2020-11-28 10:18 ` Marc Zyngier
2020-12-01 9:38 ` luojiaxing [this message]
2020-12-01 10:58 ` Marc Zyngier
2020-11-23 6:54 ` [RFC PATCH v1 2/4] KVM: arm64: GICv4.1: Try to save hw pending state in save_pending_tables Shenming Lu
2020-11-23 9:18 ` Marc Zyngier
2020-11-24 7:40 ` Shenming Lu
2020-11-24 8:26 ` Marc Zyngier
2020-11-24 13:10 ` Shenming Lu
2020-11-23 6:54 ` [RFC PATCH v1 3/4] KVM: arm64: GICv4.1: Restore VLPI's pending state to physical side Shenming Lu
2020-11-23 9:27 ` Marc Zyngier
2020-11-24 8:10 ` Shenming Lu
2020-11-24 8:44 ` Marc Zyngier
2020-11-24 13:12 ` Shenming Lu
2020-11-30 7:23 ` Shenming Lu
2020-12-01 10:55 ` Marc Zyngier
2020-12-01 11:40 ` Shenming Lu
2020-12-01 11:50 ` Marc Zyngier
2020-12-01 12:15 ` Shenming Lu
2020-12-08 8:25 ` Shenming Lu
2020-12-16 10:35 ` Auger Eric
2020-12-17 4:19 ` Shenming Lu
2020-11-23 6:54 ` [RFC PATCH v1 4/4] KVM: arm64: GICv4.1: Give a chance to save VLPI's pending state Shenming Lu
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