linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Don't need VSYNC if VMAPP with {V, Alloc}=={0, x}

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Message-ID: <8532b19b-361e-2234-92db-83f4d56bae19@huawei.com>
Date: Tue, 2 Apr 2024 21:32:40 +0800
From: Tangnianyao <tangnianyao@...wei.com>
To: Marc Zyngier <maz@...nel.org>
CC: <tglx@...utronix.de>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <guoyang2@...wei.com>,
	<wangwudi@...ilicon.com>
Subject: Re: [PATCH] irqchip/gic-v3-its: Don't need VSYNC if VMAPP with {V,
 Alloc}=={0, x}



On 4/2/2024 20:35, Marc Zyngier wrote:
> On Tue, 02 Apr 2024 12:41:47 +0100,
> t00849498 <tangnianyao@...wei.com> wrote:
>> From GIC spec, a VMAPP with {V, Alloc}=={0, x} is self-synchronizing,
> It'd be nice to quote the part of the spec (5.3.19).
yes, that's quote from GIC spec.
>> This means the ITS command queue does not show the command as
>> consumed until all of its effects are completed. A VSYNC with unmapped
>> vpeid is not needed.
>>
>> Signed-off-by: t00849498 <tangnianyao@...wei.com>
> Previous contributions with the same email address had the name
> "Nianyao Tang" associated with it. Was it wrong in the past? Or is the
> above wrong?
Sorry, the above name is wrong, should be "Nianyao Tang".
>
>> ---
>>  drivers/irqchip/irq-gic-v3-its.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index fca888b36680..a0ca5dcbb245 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -789,6 +789,7 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
>>  	unsigned long vpt_addr, vconf_addr;
>>  	u64 target;
>>  	bool alloc;
>> +	bool unmap_v4_1 = !desc->its_vmapp_cmd.valid && is_v4_1(its);
>>
>>  	its_encode_cmd(cmd, GITS_CMD_VMAPP);
>>  	its_encode_vpeid(cmd, desc->its_vmapp_cmd.vpe->vpe_id);
>> @@ -832,6 +833,9 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
>>  out:
>>  	its_fixup_cmd(cmd);
>>  
>> +	if (unmap_v4_1)
>> +		return NULL;
>> +
>>  	return valid_vpe(its, desc->its_vmapp_cmd.vpe);
>>  }
>>  
> This is a bit ugly. We already have a whole block dedicated to
> handling VMAPP with V=0 and GICv4.1, and it'd be more readable to keep
> all that code together. Something like the untested patch below.

Thank you for quick fix, it would be great to remove this VSYNC. ITS handling VSYNC unmap
vpeid may waste some time, trigger exception and needed to be handled.

> Thanks,
>
> 	M.
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index fca888b36680..2a537cbfcb07 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -786,6 +786,7 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
>  					   struct its_cmd_block *cmd,
>  					   struct its_cmd_desc *desc)
>  {
> +	struct its_vpe *vpe = valid_vpe(its, desc->its_vmapp_cmd.vpe);
>  	unsigned long vpt_addr, vconf_addr;
>  	u64 target;
>  	bool alloc;
> @@ -798,6 +799,11 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
>  		if (is_v4_1(its)) {
>  			alloc = !atomic_dec_return(&desc->its_vmapp_cmd.vpe->vmapp_count);
>  			its_encode_alloc(cmd, alloc);
> +			/*
> +			 * Unmapping a VPE is self-synchronizing on GICv4.1,
> +			 * no need to issue a VSYNC.
> +			 */
> +			vpe = NULL;
>  		}
>  
>  		goto out;
> @@ -832,7 +838,7 @@ static struct its_vpe *its_build_vmapp_cmd(struct its_node *its,
>  out:
>  	its_fixup_cmd(cmd);
>  
> -	return valid_vpe(its, desc->its_vmapp_cmd.vpe);
> +	return vpe;
>  }
>  
>  static struct its_vpe *its_build_vmapti_cmd(struct its_node *its,
>