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From: Marc Zyngier <maz@kernel.org>
To: Zenghui Yu <yuzenghui@huawei.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Jason Cooper <jason@lakedaemon.net>,
	jiayanlei@huawei.com, linux-kernel@vger.kernel.org,
	Robert Richter <rrichter@marvell.com>,
	Jayachandran C <jnair@marvell.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	liangboyan@hisilicon.com, kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v2 12/36] irqchip/gic-v4.1: Implement the v4.1 flavour of VMAPP
Date: Wed, 13 Nov 2019 10:56:22 +0109
Message-ID: <c3830faf33c7f8b983ad4863fe02b86b@www.loen.fr> (raw)
In-Reply-To: <c9ef4c0f-bb34-82ff-c286-8430c1c7c583@huawei.com>

Hi Zenghui,

On 2019-11-13 09:11, Zenghui Yu wrote:
> Hi Marc,
>
> On 2019/10/27 22:42, Marc Zyngier wrote:
>> The ITS VMAPP command gains some new fields with GICv4.1:
>> - a default doorbell, which allows a single doorbell to be used for
>>    all the VLPIs routed to a given VPE
>> - a pointer to the configuration table (instead of having it in a 
>> register
>>    that gets context switched)
>> - a flag indicating whether this is the first map or the last unmap 
>> for
>>    this particulat VPE
>> - a flag indicating whether the pending table is known to be zeroed, 
>> or not
>> Plumb in the new fields in the VMAPP builder, and add the map/unmap
>> refcounting so that the ITS can do the right thing.
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>
> [...]
>
>> @@ -605,19 +626,45 @@ static struct its_vpe 
>> *its_build_vmapp_cmd(struct its_node *its,
>>   					   struct its_cmd_block *cmd,
>>   					   struct its_cmd_desc *desc)
>>   {
>> -	unsigned long vpt_addr;
>> +	unsigned long vpt_addr, vconf_addr;
>>   	u64 target;
>> -
>> -	vpt_addr = 
>> virt_to_phys(page_address(desc->its_vmapp_cmd.vpe->vpt_page));
>> -	target = desc->its_vmapp_cmd.col->target_address + 
>> its->vlpi_redist_offset;
>> +	bool alloc;
>>
>>   	its_encode_cmd(cmd, GITS_CMD_VMAPP);
>>   	its_encode_vpeid(cmd, desc->its_vmapp_cmd.vpe->vpe_id);
>>   	its_encode_valid(cmd, desc->its_vmapp_cmd.valid);
>> +
>> +	if (!desc->its_vmapp_cmd.valid) {
>> +		if (is_v4_1(its)) {
>> +			alloc = 
>> !atomic_dec_return(&desc->its_vmapp_cmd.vpe->vmapp_count);
>> +			its_encode_alloc(cmd, alloc);
>> +		}
>> +
>> +		goto out;
>> +	}
>> +
>> +	vpt_addr = 
>> virt_to_phys(page_address(desc->its_vmapp_cmd.vpe->vpt_page));
>> +	target = desc->its_vmapp_cmd.col->target_address + 
>> its->vlpi_redist_offset;
>> +
>>   	its_encode_target(cmd, target);
>>   	its_encode_vpt_addr(cmd, vpt_addr);
>>   	its_encode_vpt_size(cmd, LPI_NRBITS - 1);
>>   +	if (!is_v4_1(its))
>> +		goto out;
>> +
>> +	vconf_addr = 
>> virt_to_phys(page_address(desc->its_vmapp_cmd.vpe->its_vm->vprop_page));
>> +
>> +	alloc = 
>> atomic_inc_and_test(&desc->its_vmapp_cmd.vpe->vmapp_count);
>
> As the comment block on top of atomic_inc_and_test(atomic *v) says,
>
>  * Atomically increments @v by 1
>  * and returns true if the result is zero, or false for all
>  * other cases.
>  */
>
> We will always get the 'alloc' as false here, even if this is the
> first mapping of this vPE.  This is not as expected, I think.

As usual, a very good observation!

Indeed, I cocked up the logic here, as we need to test the value before
the increment (and not after). What we want is probably something like:

   alloc = !atomic_fetch_inc(&desc->its_vmapp_cmd.vpe->vmapp_count);

> And on the other hand, I wonder what is the reason for 'vmapp_count'
> to be atomic_t?

The rational is that we could end-up with multiple VMAPP commands 
emitted
in parallel, for example. That's probably not strictly necessary right 
now,
but I'm trying to be cautious.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...
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  reply index

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-27 14:41 [PATCH v2 00/36] irqchip/gic-v4: GICv4.1 architecture support Marc Zyngier
2019-10-27 14:41 ` [PATCH v2 01/36] KVM: arm64: vgic-v4: Move the GICv4 residency flow to be driven by vcpu_load/put Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 02/36] irqchip/gic-v3-its: Factor out wait_for_syncr primitive Marc Zyngier
2019-10-28  9:20   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 03/36] irqchip/gic-v3-its: Allow LPI invalidation via the DirectLPI interface Marc Zyngier
2019-10-31  8:49   ` Zenghui Yu
2019-11-01 13:26     ` Marc Zyngier
2019-11-05 10:30       ` Zenghui Yu
2019-11-05 12:12         ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 04/36] irqchip/gic-v3-its: Make is_v4 use a TYPER copy Marc Zyngier
2019-10-28  9:34   ` Zenghui Yu
2019-10-28 10:52     ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 05/36] irqchip/gic-v3-its: Kill its->ite_size and use TYPER copy instead Marc Zyngier
2019-10-28  9:40   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 06/36] irqchip/gic-v3-its: Kill its->device_ids " Marc Zyngier
2019-10-31  6:33   ` Zenghui Yu
2019-10-31  8:30     ` Marc Zyngier
2019-10-31  9:08       ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 07/36] irqchip/gic-v3-its: Add get_vlpi_map() helper Marc Zyngier
2019-10-31  3:54   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 08/36] irqchip/gic-v3: Detect GICv4.1 supporting RVPEID Marc Zyngier
2019-10-31 11:34   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 09/36] irqchip/gic-v3: Add GICv4.1 VPEID size discovery Marc Zyngier
2019-10-31 12:02   ` Zenghui Yu
2019-11-01 15:13     ` Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 10/36] irqchip/gic-v3: Workaround Cavium TX1 erratum when reading GICD_TYPER2 Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 11/36] irqchip/gic-v4.1: VPE table (aka GICR_VPROPBASER) allocation Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 12/36] irqchip/gic-v4.1: Implement the v4.1 flavour of VMAPP Marc Zyngier
2019-11-01 10:58   ` Zenghui Yu
2019-11-13  8:02   ` Zenghui Yu
2019-11-13  9:47     ` Marc Zyngier [this message]
2019-10-27 14:42 ` [PATCH v2 13/36] irqchip/gic-v4.1: Don't use the VPE proxy if RVPEID is set Marc Zyngier
2019-11-01 11:05   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 14/36] irqchip/gic-v4.1: Implement the v4.1 flavour of VMOVP Marc Zyngier
2019-11-01 11:10   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 15/36] irqchip/gic-v4.1: Plumb skeletal VPE irqchip Marc Zyngier
2019-11-01 11:13   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 16/36] irqchip/gic-v4.1: Add mask/unmask doorbell callbacks Marc Zyngier
2019-11-01 11:23   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 17/36] irqchip/gic-v4.1: Add VPE residency callback Marc Zyngier
2019-11-01 11:34   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 18/36] irqchip/gic-v4.1: Add VPE eviction callback Marc Zyngier
2019-11-01 11:39   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 19/36] irqchip/gic-v4.1: Add VPE INVALL callback Marc Zyngier
2019-11-01 11:51   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 20/36] irqchip/gic-v4.1: Suppress per-VLPI doorbell Marc Zyngier
2019-11-01 12:17   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 21/36] irqchip/gic-v4.1: Allow direct invalidation of VLPIs Marc Zyngier
2019-11-01 12:30   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 22/36] irqchip/gic-v4.1: Advertise support v4.1 to KVM Marc Zyngier
2019-11-01 12:55   ` Zenghui Yu
2019-10-27 14:42 ` [PATCH v2 23/36] irqchip/gic-v4.1: Map the ITS SGIR register page Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 24/36] irqchip/gic-v4.1: Plumb skeletal VSGI irqchip Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 25/36] irqchip/gic-v4.1: Add initial SGI configuration Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 26/36] irqchip/gic-v4.1: Plumb mask/unmask SGI callbacks Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 27/36] irqchip/gic-v4.1: Plumb get/set_irqchip_state " Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 28/36] irqchip/gic-v4.1: Plumb set_vcpu_affinity " Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 29/36] irqchip/gic-v4.1: Move doorbell management to the GICv4 abstraction layer Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 30/36] irqchip/gic-v4.1: Add VSGI allocation/teardown Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 31/36] irqchip/gic-v4.1: Add VSGI property setup Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 32/36] irqchip/gic-v4.1: Eagerly vmap vPEs Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 33/36] KVM: arm64: GICv4.1: Let doorbells be auto-enabled Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 34/36] KVM: arm64: GICv4.1: Add direct injection capability to SGI registers Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 35/36] KVM: arm64: GICv4.1: Configure SGIs as HW interrupts Marc Zyngier
2019-10-27 14:42 ` [PATCH v2 36/36] KVM: arm64: GICv4.1: Expose HW-based SGIs in debugfs Marc Zyngier

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