linux-kernel - Re: [PATCH v2 03/36] irqchip/gic-v3-its: Allow LPI invalidation via the DirectLPI interface

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Date:   Tue, 05 Nov 2019 13:21:34 +0109
From:   Marc Zyngier <maz@...nel.org>
To:     Zenghui Yu <yuzenghui@...wei.com>
Cc:     <kvmarm@...ts.cs.columbia.edu>, <linux-kernel@...r.kernel.org>,
        Eric Auger <eric.auger@...hat.com>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Andrew Murray <andrew.murray@....com>,
        Jayachandran C <jnair@...vell.com>,
        Robert Richter <rrichter@...vell.com>
Subject: Re: [PATCH v2 03/36] irqchip/gic-v3-its: Allow LPI invalidation via  the DirectLPI interface

On 2019-11-05 11:39, Zenghui Yu wrote:
> Hi Marc,
>
> On 2019/11/1 21:26, Marc Zyngier wrote:
>> On Thu, 31 Oct 2019 08:49:32 +0000,
>> Zenghui Yu <yuzenghui@...wei.com> wrote:
>>>
>>> But this patch really drives me to look through all callsites of
>>> dev_event_to_col(), the abstraction which can be used _only_ with
>>> physical LPI mappings.
>>>
>>> I find that when building the INV command, we use 
>>> dev_event_to_col()
>>> to find the "sync_obj" and then pass it to the following SYNC 
>>> command.
>>> But the "INV+SYNC" will be performed both on physical LPI and 
>>> *VLPI*
>>> (lpi_update_config/its_send_inv).
>>> So I have two questions about the way we sending INV on VLPI:
>>>
>>> 1) Which "sync" command should be followed?  SYNC or VSYNC?
>>> (we currently use SYNC, while the spec says, SYNC "ensures all
>>> outstanding ITS operations associated with *physical* interrupts
>>> for the Redistributor are globally observed ...")
>>>
>>> 2) The "sync_obj" we are currently using seems to be wrong.
>> I think you're right on both counts (where were you when I wrote the
>> initial GICv4 support? ;-). I think the confusion stems from the 
>> fact
>
> (I'm a bit late here :-).
>
>> that there is no 'VINV' command, and we simply overlooked the sync
>> object issue. It is quite likely that existing implementations don't
>> care much about the difference (otherwise we'd have seen the problem
>> before), but it doesn't hurt to do the right thing.
>> I have the following patch as part of a set of fixes that I'm about 
>> to
>> post (once I get a chance to test them), let me know what you think.
>>
>> 	M.
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
>> b/drivers/irqchip/irq-gic-v3-its.c
>> index a47ed2ba2907..75ab3716a870 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -702,6 +702,24 @@ static struct its_vpe 
>> *its_build_vmovp_cmd(struct its_node *its,
>>   	return valid_vpe(its, desc->its_vmovp_cmd.vpe);
>>   }
>>   +static struct its_vpe *its_build_vinv_cmd(struct its_node *its,
>> +					  struct its_cmd_block *cmd,
>> +					  struct its_cmd_desc *desc)
>> +{
>> +	struct its_vlpi_map *map;
>> +
>> +	map = dev_event_to_vlpi_map(desc->its_inv_cmd.dev,
>> +				    desc->its_inv_cmd.event_id);
>
> Indeed!  I think we need this kind of abstraction for VLPI.

Yeah, I finally realised we'd needed something like that, and made
it part of the get_vlpi_map() patch.

>
>> +
>> +	its_encode_cmd(cmd, GITS_CMD_INV);
>> +	its_encode_devid(cmd, desc->its_inv_cmd.dev->device_id);
>> +	its_encode_event_id(cmd, desc->its_inv_cmd.event_id);
>> +
>> +	its_fixup_cmd(cmd);
>> +
>> +	return valid_vpe(its, map->vpe);
>> +}
>> +
>>   static u64 its_cmd_ptr_to_offset(struct its_node *its,
>>   				 struct its_cmd_block *ptr)
>>   {
>> @@ -1068,6 +1086,20 @@ static void its_send_vinvall(struct its_node 
>> *its, struct its_vpe *vpe)
>>   	its_send_single_vcommand(its, its_build_vinvall_cmd, &desc);
>>   }
>>   +static void its_send_vinv(struct its_device *dev, u32 event_id)
>> +{
>> +	struct its_cmd_desc desc;
>> +
>> +	/*
>> +	 * There is no real VINV command. This is just a normal INV,
>> +	 * with a VSYNC instead of a SYNC.
>> +	 */
>> +	desc.its_inv_cmd.dev = dev;
>> +	desc.its_inv_cmd.event_id = event_id;
>> +
>> +	its_send_single_vcommand(dev->its, its_build_vinv_cmd, &desc);
>> +}
>> +
>>   /*
>>    * irqchip functions - assumes MSI, mostly.
>>    */
>> @@ -1142,8 +1174,10 @@ static void lpi_update_config(struct irq_data 
>> *d, u8 clr, u8 set)
>>   	lpi_write_config(d, clr, set);
>>   	if (gic_rdists->has_direct_lpi && !irqd_is_forwarded_to_vcpu(d))
>>   		direct_lpi_inv(d);
>> -	else
>> +	else if (!irqd_is_forwarded_to_vcpu(d))
>>   		its_send_inv(its_dev, its_get_event_id(d));
>> +	else
>> +		its_send_vinv(its_dev, its_get_event_id(d));
>
> Yeah, this is exactly what I was having in the mind when reporting 
> this
> problem - "maybe we should have a SW emulated VINV+VSYNC for VLPI".
> So I think this patch has done the right thing.
>
> And what about the INT and CLEAR?  In response to guest's INT/CLEAR
> commands, hypervisor (I mean KVM) will bother the ITS driver to send
> INT/CLEAR for VLPIs.  They're both followed by SYNC and might need 
> the
> same fixes?

Yup. Please see this series[1], which has grown quite a few fixups,
including some pretty old ones (I've just pushed an update, and should
post it shortly).

Thanks,

         M.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/gic-5.5-wip
-- 
Jazz is not dead. It just smells funny...