Linux Virtualization - Apr 2019 - [RFC PATCH 03/12] s390/mm: force swiotlb for protected virtualization

On Fri,  5 Apr 2019 01:16:13 +0200
Halil Pasic <pasic at linux.ibm.com> wrote:
> On s390 protected virtualization guests also have to use bounce I/O
> buffers.  That requires some plumbing.
> 
> Let us make sure any device using DMA API accordingly is spared from the
> problems that hypervisor attempting I/O to a non-shared secure page would
> bring.
I have problems parsing this sentence :(

Do you mean that we want to exclude pages for I/O from encryption?
> 
> Signed-off-by: Halil Pasic <pasic at linux.ibm.com>
> ---
>  arch/s390/Kconfig                   |  4 ++++
>  arch/s390/include/asm/Kbuild        |  1 -
>  arch/s390/include/asm/dma-mapping.h | 13 +++++++++++
>  arch/s390/include/asm/mem_encrypt.h | 18 +++++++++++++++
>  arch/s390/mm/init.c                 | 44
+++++++++++++++++++++++++++++++++++++
>  5 files changed, 79 insertions(+), 1 deletion(-)
>  create mode 100644 arch/s390/include/asm/dma-mapping.h
>  create mode 100644 arch/s390/include/asm/mem_encrypt.h
(...)
> @@ -126,6 +129,45 @@ void mark_rodata_ro(void)
>  	pr_info("Write protected read-only-after-init data: %luk\n",
size >> 10);
>  }
>  
> +int set_memory_encrypted(unsigned long addr, int numpages)
> +{
> +	/* also called for the swiotlb bounce buffers, make all pages shared */
> +	/* TODO: do ultravisor calls */
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(set_memory_encrypted);
> +
> +int set_memory_decrypted(unsigned long addr, int numpages)
> +{
> +	/* also called for the swiotlb bounce buffers, make all pages shared */
> +	/* TODO: do ultravisor calls */
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(set_memory_decrypted);
> +
> +/* are we a protected virtualization guest? */
> +bool sev_active(void)
> +{
> +	/*
> +	 * TODO: Do proper detection using ultravisor, for now let us fake we
> +	 *  have it so the code gets exercised.
That's the swiotlb stuff, right?

(The patches will obviously need some reordering before it is actually
getting merged.)
> +	 */
> +	return true;
> +}
> +EXPORT_SYMBOL_GPL(sev_active);
> +
> +/* protected virtualization */
> +static void pv_init(void)
> +{
> +	if (!sev_active())
> +		return;
> +
> +	/* make sure bounce buffers are shared */
> +	swiotlb_init(1);
> +	swiotlb_update_mem_attributes();
> +	swiotlb_force = SWIOTLB_FORCE;
> +}
> +
>  void __init mem_init(void)
>  {
>  	cpumask_set_cpu(0, &init_mm.context.cpu_attach_mask);
> @@ -134,6 +176,8 @@ void __init mem_init(void)
>  	set_max_mapnr(max_low_pfn);
>          high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
>  
> +	pv_init();
> +
>  	/* Setup guest page hinting */
>  	cmma_init();
>