Re: [PATCH kernel 2/2] powerpc/pseries/dma: Enable swiotlb

[Thiago Jung Bauermann <bauerman@linux.ibm.com>]

Hello Alexey,

Thanks!

I have similar changes in my "Secure Virtual Machine Enablement"
patches, which I am currently preparing for posting again real soon now.

This is the last version:

https://lore.kernel.org/linuxppc-dev/20180824162535.22798-1-bauerman@linux.ibm.com/

Alexey Kardashevskiy <aik@ozlabs.ru> writes:

> So far the pseries platforms has always been using IOMMU making SWIOTLB
> unnecessary. Now we want secure guests which means devices can only
> access certain areas of guest physical memory; we are going to use
> SWIOTLB for this purpose.
>
> This allows SWIOTLB for pseries. By default there is no change in behavior.
>
> This enables SWIOTLB when the "swiotlb" kernel parameter is set to "force".
>
> With the SWIOTLB enabled, the kernel creates a directly mapped DMA window
> (using the usual DDW mechanism) and implements SWIOTLB on top of that.
>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  arch/powerpc/platforms/pseries/setup.c | 5 +++++
>  arch/powerpc/platforms/pseries/Kconfig | 1 +
>  2 files changed, 6 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
> index e4f0dfd4ae33..30d72b587ac5 100644
> --- a/arch/powerpc/platforms/pseries/setup.c
> +++ b/arch/powerpc/platforms/pseries/setup.c
> @@ -42,6 +42,7 @@
>  #include <linux/of.h>
>  #include <linux/of_pci.h>
>  #include <linux/memblock.h>
> +#include <linux/swiotlb.h>
>
>  #include <asm/mmu.h>
>  #include <asm/processor.h>
> @@ -71,6 +72,7 @@
>  #include <asm/isa-bridge.h>
>  #include <asm/security_features.h>
>  #include <asm/asm-const.h>
> +#include <asm/swiotlb.h>
>
>  #include "pseries.h"
>  #include "../../../../drivers/pci/pci.h"
> @@ -797,6 +799,9 @@ static void __init pSeries_setup_arch(void)
>  	}
>
>  	ppc_md.pcibios_root_bridge_prepare = pseries_root_bridge_prepare;
> +
> +	if (swiotlb_force == SWIOTLB_FORCE)
> +		ppc_swiotlb_enable = 1;
>  }

Yep! I have this here, enabled when booting as a secure guest:

https://lore.kernel.org/linuxppc-dev/20180824162535.22798-6-bauerman@linux.ibm.com/

And also another patch which makes it so that if booting as a secure
guest it acts as if the swiotlb kernel parameter was set to force:

https://lore.kernel.org/linuxppc-dev/20180824162535.22798-11-bauerman@linux.ibm.com/

>  static void pseries_panic(char *str)
> diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
> index 9c6b3d860518..b9e8b608de01 100644
> --- a/arch/powerpc/platforms/pseries/Kconfig
> +++ b/arch/powerpc/platforms/pseries/Kconfig
> @@ -23,6 +23,7 @@ config PPC_PSERIES
>  	select ARCH_RANDOM
>  	select PPC_DOORBELL
>  	select FORCE_SMP
> +	select SWIOTLB
>  	default y
>
>  config PPC_SPLPAR

I put this in a PPC_SVM config option:

https://lore.kernel.org/linuxppc-dev/20180824162535.22798-3-bauerman@linux.ibm.com/

--
Thiago Jung Bauermann
IBM Linux Technology Center