linux-kernel - Re: [PATCH] drivers: irqchip: Allocate alignment addr by ITS_BASER.Page

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Message-ID: <87tu7h4d78.wl-maz@kernel.org>
Date:   Sat, 16 Jul 2022 10:30:19 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     wangwudi <wangwudi@...ilicon.com>
Cc:     <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] drivers: irqchip: Allocate alignment addr by ITS_BASER.Page_size

On Sat, 16 Jul 2022 08:05:36 +0100,
wangwudi <wangwudi@...ilicon.com> wrote:
> 
> The description of the ITS_BASER.Physical_Address field in the ARM GIC spec is as 
> follows:
> "The address must be aligned to the size specified in the Page Size field."
> The Page_Size field in ITS_BASER might be RO.
> 
> Currently, the address is aligned based on the system page_size, not the HW 
> Page_Size field. In some case, this is in contradiction with the spec.
> 
> For example:
> ITS_BASER.Page_Size indicate 16K, and kernel page size is 4K.
> If HW need 4K-size memory, the driver may alloc a 4K aligned address.
> This has been proven in hardware.

Ah, interesting bug. Thanks for bringing this up. Can you describe how
this occurs? I suspect you are using indirect tables.

> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Marc Zyngier <maz@...nel.org>
> Signed-off-by: wangwudi <wangwudi@...ilicon.com>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 5ff09de6c48f..0e25e887d45c 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -2310,6 +2310,9 @@ static int its_setup_baser(struct its_node *its, struct its_baser *baser,
>  		order = get_order(GITS_BASER_PAGES_MAX * psz);
>  	}
>  
> +	if ((psz > PAGE_SIZE) && (PAGE_ORDER_TO_SIZE(order) < psz)) {
> +		order = get_order(psz);
> +	}
>  	page = alloc_pages_node(its->numa_node, GFP_KERNEL | __GFP_ZERO, order);
>  	if (!page)
>  		return -ENOMEM;

However, I don't see how you end-up with the incorrect value here.

* No indirect table:
	alloc_its_tables():
		order = get_order(baser->psz);

* Indirect tables:
	alloc_its_tables():
		order = get_order(baser->psz);
	its_parse_indirect_baser():
		new_order = *order;
		new_order = max_t(u32, get_order(esz << ids), new_order);

So in both cases, we should end-up with order >= get_order(psz).

Clearly, I'm missing a path, but your commit message doesn't make it
obvious. Can you please enlighten me?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.