On Sat, Aug 15, 2020 at 05:45:36PM -0300, Thiago Jung Bauermann wrote:
> POWER secure guests (i.e., guests which use the Protection Execution
> Facility) need to use SWIOTLB to be able to do I/O with the hypervisor, but
> they don't need the SWIOTLB memory to be in low addresses since the
> hypervisor doesn't have any addressing limitation.
>
> This solves a SWIOTLB initialization problem we are seeing in secure guests
> with 128 GB of RAM: they are configured with 4 GB of crashkernel reserved
> memory, which leaves no space for SWIOTLB in low addresses.
What about just open coding the allocation and using
swiotlb_init_with_tbl?
>
> Signed-off-by: Thiago Jung Bauermann <bauer...@linux.ibm.com>
> ---
> arch/powerpc/mm/mem.c | 7 ++++++-
> include/linux/swiotlb.h | 8 +++++++-
> kernel/dma/swiotlb.c | 10 +++++++---
> 3 files changed, 20 insertions(+), 5 deletions(-)
>
> Normally I would split changes like this into one patch touching generic
> code and another for the arch-specific part, but in this case I thought it
> would be unneeded complexity. I can split though if people prefer it that
> way.
>
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index c2c11eb8dcfc..13f2e3aff8b5 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -50,6 +50,7 @@
> #include <asm/swiotlb.h>
> #include <asm/rtas.h>
> #include <asm/kasan.h>
> +#include <asm/svm.h>
>
> #include <mm/mmu_decl.h>
>
> @@ -290,7 +291,11 @@ void __init mem_init(void)
> * back to to-down.
> */
> memblock_set_bottom_up(true);
> - swiotlb_init(0);
> + /*
> + * SVM guests can use the SWIOTLB wherever it is in memory,
> + * even if not DMA-able.
> + */
> + swiotlb_init_anywhere(0, is_secure_guest());
> #endif
>
> high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 046bb94bd4d6..433f3dbb35b5 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -29,7 +29,13 @@ enum swiotlb_force {
> */
> #define IO_TLB_SHIFT 11
>
> -extern void swiotlb_init(int verbose);
> +void __init swiotlb_init_anywhere(int verbose, bool allocate_anywhere);
> +
> +static inline void swiotlb_init(int verbose)
> +{
> + swiotlb_init_anywhere(verbose, false);
> +}
> +
> int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
> extern unsigned long swiotlb_nr_tbl(void);
> unsigned long swiotlb_size_or_default(void);
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index c19379fabd20..27070aa59e34 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -244,7 +244,7 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long
> nslabs, int verbose)
> * structures for the software IO TLB used to implement the DMA API.
> */
> void __init
> -swiotlb_init(int verbose)
> +swiotlb_init_anywhere(int verbose, bool allocate_anywhere)
> {
> size_t default_size = IO_TLB_DEFAULT_SIZE;
> unsigned char *vstart;
> @@ -257,8 +257,12 @@ swiotlb_init(int verbose)
>
> bytes = io_tlb_nslabs << IO_TLB_SHIFT;
>
> - /* Get IO TLB memory from the low pages */
> - vstart = memblock_alloc_low(PAGE_ALIGN(bytes), PAGE_SIZE);
> + if (allocate_anywhere)
> + vstart = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
> + else
> + /* Get IO TLB memory from the low pages */
> + vstart = memblock_alloc_low(PAGE_ALIGN(bytes), PAGE_SIZE);
> +
> if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, verbose))
> return;
>
---end quoted text---
