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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 and/or performance degradation for > > high I/O workloads. > > > > Increase the default size of SWIOTLB for SEV guests > > using a minimum value of 128MB and a maximum value > > > > 64MB for a 1GB VM is not enough? > > > of 512MB, determining on amount of provisioned guest > > I like the implementation on how this is done.. but > the choices of memory and how much seems very much > random. Could there be some math behind this? > Earlier the patch was based on using a % of guest memory, as below: +#define SEV_ADJUST_SWIOTLB_SIZE_PERCENT 5 +#define SEV_ADJUST_SWIOTLB_SIZE_MAX (1UL << 30) ... ... + if (sev_active() && !io_tlb_nslabs) { + unsigned long total_mem = get_num_physpages() << PAGE_SHIFT; + + default_size = total_mem * + SEV_ADJUST_SWIOTLB_SIZE_PERCENT / 100; + + default_size = ALIGN(default_size, 1 << IO_TLB_SHIFT); + + default_size = clamp_val(default_size, IO_TLB_DEFAULT_SIZE, + SEV_ADJUST_SWIOTLB_SIZE_MAX); + } But, then it is difficult to predict what % of guest memory to use ? Then there are other factors to consider, such as vcpu_count or if there is going to be high I/O workload, etc. But that all makes it very complicated, what we basically want is a range from 128M to 512M and that's why the current patch which picks up this range from the amount of allocated guest memory keeps it simple. Thanks, Ashish > > memory. > > > > Using late_initcall() interface to invoke > > swiotlb_adjust() does not work as the size > > adjustment needs to be done before mem_encrypt_init() > > and reserve_crashkernel() which use the allocated > > SWIOTLB buffer size, hence calling it explicitly > > from setup_arch(). > > > > 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. > > > > Signed-off-by: Ashish Kalra > > --- > > arch/x86/kernel/setup.c | 2 ++ > > arch/x86/mm/mem_encrypt.c | 42 +++++++++++++++++++++++++++++++++++++++ > > include/linux/swiotlb.h | 1 + > > kernel/dma/swiotlb.c | 27 +++++++++++++++++++++++++ > > 4 files changed, 72 insertions(+) > > > > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > > index 3511736fbc74..b073d58dd4a3 100644 > > --- a/arch/x86/kernel/setup.c > > +++ b/arch/x86/kernel/setup.c > > @@ -1166,6 +1166,8 @@ void __init setup_arch(char **cmdline_p) > > if (boot_cpu_has(X86_FEATURE_GBPAGES)) > > hugetlb_cma_reserve(PUD_SHIFT - PAGE_SHIFT); > > > > + swiotlb_adjust(); > > + > > /* > > * Reserve memory for crash kernel after SRAT is parsed so that it > > * won't consume hotpluggable memory. > > diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c > > index 3f248f0d0e07..e0deb157cddd 100644 > > --- a/arch/x86/mm/mem_encrypt.c > > +++ b/arch/x86/mm/mem_encrypt.c > > @@ -489,7 +489,49 @@ static void print_mem_encrypt_feature_info(void) > > pr_cont("\n"); > > } > > > > +#define TOTAL_MEM_1G 0x40000000UL > > +#define TOTAL_MEM_4G 0x100000000UL > > + > > +#define SIZE_128M (128UL<<20) > > +#define SIZE_256M (256UL<<20) > > +#define SIZE_512M (512UL<<20) > > + > > /* Architecture __weak replacement functions */ > > +unsigned long __init arch_swiotlb_adjust(unsigned long iotlb_default_size) > > +{ > > + unsigned long size = 0; > > + > > + /* > > + * 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 DMA, resulting in I/O errors and/or > > + * performance degradation especially with high I/O workloads. > > + * Increase the default size of SWIOTLB for SEV guests using > > + * a minimum value of 128MB and a maximum value of 512MB, > > + * depending on amount of provisioned guest memory. > > + */ > > + if (sev_active()) { > > + phys_addr_t total_mem = memblock_phys_mem_size(); > > + > > + if (total_mem <= TOTAL_MEM_1G) > > + size = clamp(iotlb_default_size * 2, SIZE_128M, > > + SIZE_128M); > > + else if (total_mem <= TOTAL_MEM_4G) > > + size = clamp(iotlb_default_size * 4, SIZE_256M, > > + SIZE_256M); > > + else > > + size = clamp(iotlb_default_size * 8, SIZE_512M, > > + SIZE_512M); > > + > > + pr_info("SEV adjusted max SWIOTLB size = %luMB", > > + size >> 20); > > + } > > + > > + return size; > > +} > > + > > void __init mem_encrypt_init(void) > > { > > if (!sme_me_mask) > > diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h > > index 046bb94bd4d6..01ae6d891327 100644 > > --- a/include/linux/swiotlb.h > > +++ b/include/linux/swiotlb.h > > @@ -33,6 +33,7 @@ extern void swiotlb_init(int verbose); > > 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); > > +extern void __init swiotlb_adjust(void); > > extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs); > > extern void __init swiotlb_update_mem_attributes(void); > > > > diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c > > index c19379fabd20..66a9e627bb51 100644 > > --- a/kernel/dma/swiotlb.c > > +++ b/kernel/dma/swiotlb.c > > @@ -163,6 +163,33 @@ unsigned long swiotlb_size_or_default(void) > > return size ? size : (IO_TLB_DEFAULT_SIZE); > > } > > > > +unsigned long __init __weak arch_swiotlb_adjust(unsigned long size) > > +{ > > + return 0; > > +} > > + > > +void __init swiotlb_adjust(void) > > +{ > > + unsigned long size; > > + > > + /* > > + * If swiotlb parameter has not been specified, give a chance to > > + * architectures such as those supporting memory encryption to > > + * adjust/expand SWIOTLB size for their use. > > + */ > > + if (!io_tlb_nslabs) { > > + size = arch_swiotlb_adjust(IO_TLB_DEFAULT_SIZE); > > + if (size) { > > + size = ALIGN(size, 1 << IO_TLB_SHIFT); > > + io_tlb_nslabs = size >> IO_TLB_SHIFT; > > + io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE); > > + > > + pr_info("architecture adjusted SWIOTLB slabs = %lu\n", > > + io_tlb_nslabs); > > + } > > + } > > +} > > + > > void swiotlb_print_info(void) > > { > > unsigned long bytes = io_tlb_nslabs << IO_TLB_SHIFT; > > -- > > 2.17.1 > > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu