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SubjectRe: [PATCH v2] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.
On Mon, Dec 09, 2019 at 11:13:46PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
>
> For SEV, all DMA to and from guest has to use shared
> (un-encrypted) pages. SEV uses SWIOTLB to make this happen
> without requiring changes to device drivers. However,
> depending on workload being run, the default 64MB of SWIOTLB
> might not be enough and SWIOTLB may run out of buffers to
> use for DMA, resulting in I/O errors.
>
> Increase the default size of SWIOTLB for SEV guests using
> a minimum value of 128MB and a maximum value of 512MB,
> determining on amount of provisioned guest memory.
>
> The SWIOTLB default size adjustment is added as an
> architecture specific interface/callback to allow
> architectures such as those supporting memory encryption
> to adjust/expand SWIOTLB size for their use.

What if this was made dynamic? That is if there is a memory
pressure you end up expanding the SWIOTLB dynamically?

Also is it worth doing this calculation based on memory or
more on the # of PCI devices + their MMIO ranges size?

>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
> Changes in v2:
> - Fix compile errors as
> Reported-by: kbuild test robot <lkp@intel.com>
>
> arch/x86/Kconfig | 1 +
> arch/x86/mm/mem_encrypt.c | 36 ++++++++++++++++++++++++++++++++++++
> include/linux/dma-direct.h | 10 ++++++++++
> kernel/dma/Kconfig | 3 +++
> kernel/dma/swiotlb.c | 14 ++++++++++++--
> 5 files changed, 62 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5e8949953660..e75622e58d34 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1522,6 +1522,7 @@ config AMD_MEM_ENCRYPT
> select DYNAMIC_PHYSICAL_MASK
> select ARCH_USE_MEMREMAP_PROT
> select ARCH_HAS_FORCE_DMA_UNENCRYPTED
> + select ARCH_HAS_ADJUST_SWIOTLB_DEFAULT
> ---help---
> Say yes to enable support for the encryption of system memory.
> This requires an AMD processor that supports Secure Memory
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index a03614bd3e1a..f4bd4b431ba1 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -376,6 +376,42 @@ bool force_dma_unencrypted(struct device *dev)
> return false;
> }
>
> +#define TOTAL_MEM_1G 0x40000000U
> +#define TOTAL_MEM_4G 0x100000000U
> +
> +/*
> + * Override for SWIOTLB default size adjustment -
> + * ARCH_HAS_ADJUST_SWIOTLB_DEFAULT
> + */
> +unsigned long adjust_swiotlb_default_size(unsigned long default_size)
> +{
> + /*
> + * For SEV, all DMA has to occur via shared/unencrypted pages.
> + * SEV uses SWOTLB to make this happen without changing device
> + * drivers. However, depending on the workload being run, the
> + * default 64MB of SWIOTLB may not be enough & SWIOTLB may
> + * run out of buffers for using DMA, resulting in I/O errors.
> + * Increase the default size of SWIOTLB for SEV guests using
> + * a minimum value of 128MB and a maximum value of 512GB,
> + * depending on amount of provisioned guest memory.
> + */
> + if (sev_active()) {
> + unsigned long total_mem = get_num_physpages() << PAGE_SHIFT;
> +
> + if (total_mem <= TOTAL_MEM_1G)
> + default_size = default_size * 2;
> + else if (total_mem <= TOTAL_MEM_4G)
> + default_size = default_size * 4;
> + else
> + default_size = default_size * 8;
> +
> + pr_info_once("SEV is active, SWIOTLB default size set to %luMB\n",
> + default_size >> 20);
> + }
> +
> + return default_size;
> +}
> +
> /* Architecture __weak replacement functions */
> void __init mem_encrypt_free_decrypted_mem(void)
> {
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index 24b8684aa21d..85507d21493f 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -35,6 +35,16 @@ static inline bool force_dma_unencrypted(struct device *dev)
> }
> #endif /* CONFIG_ARCH_HAS_FORCE_DMA_UNENCRYPTED */
>
> +#ifdef CONFIG_ARCH_HAS_ADJUST_SWIOTLB_DEFAULT
> +unsigned long adjust_swiotlb_default_size(unsigned long default_size);
> +#else
> +static inline unsigned long adjust_swiotlb_default_size
> + (unsigned long default_size)
> +{
> + return default_size;
> +}
> +#endif /* CONFIG_ARCH_HAS_ADJUST_SWIOTLB_DEFAULT */
> +
> /*
> * If memory encryption is supported, phys_to_dma will set the memory encryption
> * bit in the DMA address, and dma_to_phys will clear it. The raw __phys_to_dma
> diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> index 4c103a24e380..851c4500ff88 100644
> --- a/kernel/dma/Kconfig
> +++ b/kernel/dma/Kconfig
> @@ -54,6 +54,9 @@ config ARCH_HAS_DMA_PREP_COHERENT
> config ARCH_HAS_FORCE_DMA_UNENCRYPTED
> bool
>
> +config ARCH_HAS_ADJUST_SWIOTLB_DEFAULT
> + bool
> +
> config DMA_NONCOHERENT_CACHE_SYNC
> bool
>
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 9280d6f8271e..7dd72bd88f1c 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -155,11 +155,21 @@ void swiotlb_set_max_segment(unsigned int val)
> #define IO_TLB_DEFAULT_SIZE (64UL<<20)
> unsigned long swiotlb_size_or_default(void)
> {
> + unsigned long default_size = IO_TLB_DEFAULT_SIZE;
> unsigned long size;
>
> + /*
> + * If swiotlb size/amount of slabs are not defined on kernel command
> + * line, then give a chance to architectures to adjust swiotlb
> + * size, this may be required by some architectures such as those
> + * supporting memory encryption.
> + */
> + if (!io_tlb_nslabs)
> + default_size = adjust_swiotlb_default_size(default_size);
> +
> size = io_tlb_nslabs << IO_TLB_SHIFT;
>
> - return size ? size : (IO_TLB_DEFAULT_SIZE);
> + return size ? size : default_size;
> }
>
> void swiotlb_print_info(void)
> @@ -245,7 +255,7 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
> void __init
> swiotlb_init(int verbose)
> {
> - size_t default_size = IO_TLB_DEFAULT_SIZE;
> + unsigned long default_size = swiotlb_size_or_default();
> unsigned char *vstart;
> unsigned long bytes;
>
> --
> 2.17.1
>

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