linux-kernel - Re: [PATCH v4] irqchip/gicv3-its: Avoid memory over allocation for ITEs

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Message-ID: <87lgqfmdy7.fsf@on-the-bus.cambridge.arm.com>
Date:   Tue, 02 May 2017 17:16:32 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Shanker Donthineni <shankerd@...eaurora.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Vikram Sethi <vikrams@...eaurora.org>
Subject: Re: [PATCH v4] irqchip/gicv3-its: Avoid memory over allocation for ITEs

On Sun, Apr 30 2017 at  3:36:15 pm BST, Shanker Donthineni <shankerd@...eaurora.org> wrote:
> We are always allocating extra 255Bytes of memory to handle ITE
> physical address alignment requirement. The kmalloc() satisfies
> the ITE alignment since the ITS driver is requesting a minimum
> size of ITS_ITT_ALIGN bytes.
>
> Let's try to allocate the exact amount of memory that is required
> for ITEs to avoid wastage.
>
> Signed-off-by: Shanker Donthineni <shankerd@...eaurora.org>
> ---
> Changes:
> v2: removed 'Change-Id: Ia8084189833f2081ff13c392deb5070c46a64038' from commit.
> v3: changed from IITE to ITE.
> v3: removed fallback since kmalloc() guarantees the right alignment.
>
>  drivers/irqchip/irq-gic-v3-its.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index 45ea1933..72e56f03 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -261,7 +261,6 @@ static struct its_collection *its_build_mapd_cmd(struct its_cmd_block *cmd,
>  	u8 size = ilog2(desc->its_mapd_cmd.dev->nr_ites);
>  
>  	itt_addr = virt_to_phys(desc->its_mapd_cmd.dev->itt);
> -	itt_addr = ALIGN(itt_addr, ITS_ITT_ALIGN);
>  
>  	its_encode_cmd(cmd, GITS_CMD_MAPD);
>  	its_encode_devid(cmd, desc->its_mapd_cmd.dev->device_id);
> @@ -1329,13 +1328,14 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>  	 */
>  	nr_ites = max(2UL, roundup_pow_of_two(nvecs));
>  	sz = nr_ites * its->ite_size;
> -	sz = max(sz, ITS_ITT_ALIGN) + ITS_ITT_ALIGN - 1;
> +	sz = max(sz, ITS_ITT_ALIGN);
>  	itt = kzalloc(sz, GFP_KERNEL);
>  	lpi_map = its_lpi_alloc_chunks(nvecs, &lpi_base, &nr_lpis);
>  	if (lpi_map)
>  		col_map = kzalloc(sizeof(*col_map) * nr_lpis, GFP_KERNEL);
>  
> -	if (!dev || !itt || !lpi_map || !col_map) {
> +	if (!dev || !itt || !lpi_map || !col_map ||
> +	    !IS_ALIGNED(virt_to_phys(itt), ITS_ITT_ALIGN)) {
>  		kfree(dev);
>  		kfree(itt);
>  		kfree(lpi_map);

I'm confused. Either the alignment is guaranteed (and you should
document why it is so), or it is not, and we need to handle the
non-alignment (instead of failing).

Thanks,

	M.
-- 
Jazz is not dead, it just smell funny.