linux-kernel - Re: [PATCH v2 17/29] arm_mpam: Extend reset logic to allow devices to be reset any time

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Message-ID: <20250912130216.00006d92@huawei.com>
Date: Fri, 12 Sep 2025 13:02:16 +0100
From: Jonathan Cameron <jonathan.cameron@...wei.com>
To: James Morse <james.morse@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-acpi@...r.kernel.org>, D Scott Phillips OS
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 Deacon" <will@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 17/29] arm_mpam: Extend reset logic to allow devices
 to be reset any time

On Wed, 10 Sep 2025 20:42:57 +0000
James Morse <james.morse@....com> wrote:

> cpuhp callbacks aren't the only time the MSC configuration may need to
> be reset. Resctrl has an API call to reset a class.
> If an MPAM error interrupt arrives it indicates the driver has
> misprogrammed an MSC. The safest thing to do is reset all the MSCs
> and disable MPAM.
> 
> Add a helper to reset RIS via their class. Call this from mpam_disable(),
> which can be scheduled from the error interrupt handler.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---
> Changes since v1:
>  * more complete use of _srcu helpers.
>  * Use guard macro for srcu.

I'm not seeing a strong reason for doing this for the case here and not
for cases in earlier patches like in mpam_cpu_online()  I'm a fan of using
these broadly in a given code base, so would guard(srcu) in those earlier patches
as well.

Anyhow, one other trivial thing inline that you can ignore or not as you wish.

Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>


>  * Dropped a might_sleep() - something else will bark.
> ---
>  drivers/resctrl/mpam_devices.c | 56 ++++++++++++++++++++++++++++++++--
>  1 file changed, 54 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index e7faf453b5d7..a9d3c4b09976 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -842,8 +842,6 @@ static int mpam_reset_ris(void *arg)
>  	u16 partid, partid_max;
>  	struct mpam_msc_ris *ris = arg;
>  
> -	mpam_assert_srcu_read_lock_held();
> -
>  	if (ris->in_reset_state)
>  		return 0;
>  
> @@ -1340,8 +1338,56 @@ static void mpam_enable_once(void)
>  	       mpam_partid_max + 1, mpam_pmg_max + 1);
>  }
>  
> +static void mpam_reset_component_locked(struct mpam_component *comp)
> +{
> +	struct mpam_msc *msc;
> +	struct mpam_vmsc *vmsc;
> +	struct mpam_msc_ris *ris;
> +
> +	lockdep_assert_cpus_held();
> +
> +	guard(srcu)(&mpam_srcu);
> +	list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
> +				 srcu_read_lock_held(&mpam_srcu)) {
> +		msc = vmsc->msc;

Might be worth reducing scope of msc and ris

> +
> +		list_for_each_entry_srcu(ris, &vmsc->ris, vmsc_list,
> +					 srcu_read_lock_held(&mpam_srcu)) {
> +			if (!ris->in_reset_state)
> +				mpam_touch_msc(msc, mpam_reset_ris, ris);
> +			ris->in_reset_state = true;
> +		}
> +	}
> +}