Re: [PATCH v2 4/8] s390/airq: use DMA memory for adapter interrupts

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 23 May 2019 18:22:05 +0200
Michael Mueller <mimu@linux.ibm.com> wrote:

> From: Halil Pasic <pasic@linux.ibm.com>
> 
> Protected virtualization guests have to use shared pages for airq
> notifier bit vectors, because hypervisor needs to write these bits.
> 
> Let us make sure we allocate DMA memory for the notifier bit vectors by
> replacing the kmem_cache with a dma_cache and kalloc() with
> cio_dma_zalloc().
> 
> Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
> ---
>  arch/s390/include/asm/airq.h |  2 ++
>  drivers/s390/cio/airq.c      | 32 ++++++++++++++++++++------------
>  drivers/s390/cio/cio.h       |  2 ++
>  drivers/s390/cio/css.c       |  1 +
>  4 files changed, 25 insertions(+), 12 deletions(-)

(...)

> diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
> index 789f6ecdbbcc..f09521771a32 100644
> --- a/drivers/s390/cio/css.c
> +++ b/drivers/s390/cio/css.c
> @@ -1173,6 +1173,7 @@ static int __init css_bus_init(void)
>  		goto out_unregister;
>  	}
>  	cio_dma_pool_init();
> +	airq_init();
>  	css_init_done = 1;
>  
>  	/* Enable default isc for I/O subchannels. */

Not directly related to this patch (I don't really have any comment
here), but I started looking at the code again and now I'm wondering
about chsc. I think it came up before, but I can't remember if chsc
needed special treatment... Anyway, css_bus_init() uses some chscs
early (before cio_dma_pool_init), so we could not use the pools there,
even if we wanted to. Do chsc commands either work, or else fail
benignly on a protected virt guest?