Re: [PATCH v3 2/8] s390/cio: introduce DMA pools to cio

Cornelia Huck
2019-06-03T11:37:57Z

On Wed, 29 May 2019 14:26:51 +0200
Michael Mueller <mimu@linux.ibm.com> wrote:

> From: Halil Pasic <pasic@linux.ibm.com>
>
> To support protected virtualization cio will need to make sure the
> memory used for communication with the hypervisor is DMA memory.
>
> Let us introduce one global pool for cio.
>
> Our DMA pools are implemented as a gen_pool backed with DMA pages. The
> idea is to avoid each allocation effectively wasting a page, as we
> typically allocate much less than PAGE_SIZE.
>
> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> Reviewed-by: Sebastian Ott <sebott@linux.ibm.com>
> Signed-off-by: Michael Mueller <mimu@linux.ibm.com>
> ---
> arch/s390/Kconfig | 1 +
> arch/s390/include/asm/cio.h | 11 ++++
> drivers/s390/cio/css.c | 120 ++++++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 128 insertions(+), 4 deletions(-)

(...)

> diff --git a/arch/s390/include/asm/cio.h b/arch/s390/include/asm/cio.h
> index 1727180e8ca1..43c007d2775a 100644
> --- a/arch/s390/include/asm/cio.h
> +++ b/arch/s390/include/asm/cio.h
> @@ -328,6 +328,17 @@ static inline u8 pathmask_to_pos(u8 mask)
> void channel_subsystem_reinit(void);
> extern void css_schedule_reprobe(void);
>
> +extern void *cio_dma_zalloc(size_t size);
> +extern void cio_dma_free(void *cpu_addr, size_t size);
> +extern struct device *cio_get_dma_css_dev(void);
> +
> +struct gen_pool;

That forward declaration is a bit ugly... I guess the alternative was
include hell?

> +void *cio_gp_dma_zalloc(struct gen_pool *gp_dma, struct device *dma_dev,
> + size_t size);
> +void cio_gp_dma_free(struct gen_pool *gp_dma, void *cpu_addr, size_t size);
> +void cio_gp_dma_destroy(struct gen_pool *gp_dma, struct device *dma_dev);
> +struct gen_pool *cio_gp_dma_create(struct device *dma_dev, int nr_pages);
> +
> /* Function from drivers/s390/cio/chsc.c */
> int chsc_sstpc(void *page, unsigned int op, u16 ctrl, u64 *clock_delta);
> int chsc_sstpi(void *page, void *result, size_t size);
> diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
> index aea502922646..b97618497848 100644
> --- a/drivers/s390/cio/css.c
> +++ b/drivers/s390/cio/css.c
> @@ -20,6 +20,8 @@
> #include <linux/reboot.h>
> #include <linux/suspend.h>
> #include <linux/proc_fs.h>
> +#include <linux/genalloc.h>
> +#include <linux/dma-mapping.h>
> #include <asm/isc.h>
> #include <asm/crw.h>
>
> @@ -224,6 +226,8 @@ struct subchannel *css_alloc_subchannel(struct subchannel_id schid,
> INIT_WORK(&sch->todo_work, css_sch_todo);
> sch->dev.release = &css_subchannel_release;
> device_initialize(&sch->dev);

It might be helpful to add a comment why you use 31 bit here...

> + sch->dev.coherent_dma_mask = DMA_BIT_MASK(31);
> + sch->dev.dma_mask = &sch->dev.coherent_dma_mask;
> return sch;
>
> err:
> @@ -899,6 +903,8 @@ static int __init setup_css(int nr)
> dev_set_name(&css->device, "css%x", nr);
> css->device.groups = cssdev_attr_groups;
> css->device.release = channel_subsystem_release;

...and 64 bit here.

> + css->device.coherent_dma_mask = DMA_BIT_MASK(64);
> + css->device.dma_mask = &css->device.coherent_dma_mask;
>
> mutex_init(&css->mutex);
> css->cssid = chsc_get_cssid(nr);

(...)

> @@ -1059,16 +1168,19 @@ static int __init css_bus_init(void)
> if (ret)
> goto out_unregister;
> ret = register_pm_notifier(&css_power_notifier);
> - if (ret) {
> - unregister_reboot_notifier(&css_reboot_notifier);
> - goto out_unregister;
> - }
> + if (ret)
> + goto out_unregister_rn;
> + ret = cio_dma_pool_init();
> + if (ret)
> + goto out_unregister_rn;

Don't you also need to unregister the pm notifier on failure here?

Other than that, I noticed only cosmetic issues; seems reasonable to me.

> css_init_done = 1;
>
> /* Enable default isc for I/O subchannels. */
> isc_register(IO_SCH_ISC);
>
> return 0;
> +out_unregister_rn:
> + unregister_reboot_notifier(&css_reboot_notifier);
> out_unregister:
> while (i-- > 0) {
> struct channel_subsystem *css = channel_subsystems[i];