Memory-encrypted guests use shared or unencrypted memory for DMA and may route all DMA through SWIOTLB. The default pool can therefore be too small for I/O-intensive workloads.
Move the existing x86 guest-sizing policy into the SWIOTLB core. For SWIOTLB_POOL_CC_GUEST, size the pool to 6% of guest memory, clamped between the normal default and 1 GiB. Preserve an explicit swiotlb= size. Provide swiotlb_adjusted_size() so early users, including the x86 crash kernel reservation, can account for the prospective guest pool size before SWIOTLB initialization. Use the same area-aware alignment for both the prospective and allocated sizes. Host memory encryption still selects a normal-sized shared pool and does not use the guest-sizing policy. A restricted DMA pool already provides shared bounce buffers for its devices. Record its presence during reserved-memory initialization and do not select the confidential-guest default-pool policy solely because guest memory encryption is active. Signed-off-by: Aneesh Kumar K.V (Arm) <[email protected]> --- arch/x86/include/asm/crash_reserve.h | 4 +-- arch/x86/mm/mem_encrypt.c | 24 -------------- include/linux/swiotlb.h | 6 ++++ kernel/dma/swiotlb.c | 49 +++++++++++++++++++++++++++- 4 files changed, 56 insertions(+), 27 deletions(-) diff --git a/arch/x86/include/asm/crash_reserve.h b/arch/x86/include/asm/crash_reserve.h index 7835b2cdff04..9f6b06e2f9bd 100644 --- a/arch/x86/include/asm/crash_reserve.h +++ b/arch/x86/include/asm/crash_reserve.h @@ -18,7 +18,7 @@ * no good way to detect the paging mode of the target kernel which will be * loaded for dumping. */ -extern unsigned long swiotlb_size_or_default(void); +unsigned long __init swiotlb_adjusted_size(void); #ifdef CONFIG_X86_32 # define CRASH_ADDR_LOW_MAX SZ_512M @@ -33,7 +33,7 @@ extern unsigned long swiotlb_size_or_default(void); static inline unsigned long crash_low_size_default(void) { #ifdef CONFIG_X86_64 - return max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20); + return max(swiotlb_adjusted_size() + (8UL << 20), 256UL << 20); #else return 0; #endif diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c index 95bae74fdab2..912f22ca838f 100644 --- a/arch/x86/mm/mem_encrypt.c +++ b/arch/x86/mm/mem_encrypt.c @@ -101,9 +101,6 @@ void __init mem_encrypt_init(void) void __init mem_encrypt_setup_arch(void) { - phys_addr_t total_mem = memblock_phys_mem_size(); - unsigned long size; - /* * Do RMP table fixups after the e820 tables have been setup by * e820__memory_setup(). @@ -114,27 +111,6 @@ void __init mem_encrypt_setup_arch(void) if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) return; - /* - * For SEV and TDX, all DMA has to occur via shared/unencrypted pages. - * Kernel uses SWIOTLB to make this happen without changing device - * drivers. However, depending on the workload being run, the - * default 64MB of SWIOTLB may not be enough and SWIOTLB may - * run out of buffers for DMA, resulting in I/O errors and/or - * performance degradation especially with high I/O workloads. - * - * Adjust the default size of SWIOTLB using a percentage of guest - * memory for SWIOTLB buffers. Also, as the SWIOTLB bounce buffer - * memory is allocated from low memory, ensure that the adjusted size - * is within the limits of low available memory. - * - * The percentage of guest memory used here for SWIOTLB buffers - * is more of an approximation of the static adjustment which - * 64MB for <1G, and ~128M to 256M for 1G-to-4G, i.e., the 6% - */ - size = total_mem * 6 / 100; - size = clamp_val(size, IO_TLB_DEFAULT_SIZE, SZ_1G); - swiotlb_adjust_size(size); - /* Set restricted memory access for virtio. */ virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc); } diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h index d69370c08094..be3962a33fc6 100644 --- a/include/linux/swiotlb.h +++ b/include/linux/swiotlb.h @@ -193,6 +193,7 @@ void swiotlb_dev_init(struct device *dev); size_t swiotlb_max_mapping_size(struct device *dev); bool is_swiotlb_allocated(void); bool is_swiotlb_active(struct device *dev); +unsigned long __init swiotlb_adjusted_size(void); void __init swiotlb_adjust_size(unsigned long size); phys_addr_t default_swiotlb_base(void); phys_addr_t default_swiotlb_limit(void); @@ -232,6 +233,11 @@ static inline bool is_swiotlb_active(struct device *dev) return false; } +static inline unsigned long __init swiotlb_adjusted_size(void) +{ + return 0; +} + static inline void swiotlb_adjust_size(unsigned long size) { } diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 90e0bfd0715c..c4611b2c4540 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -80,6 +80,7 @@ struct io_tlb_slot { static bool swiotlb_force_bounce; static bool swiotlb_force_disable; +static bool restricted_dma_pool_present __initdata; enum swiotlb_pool_policy { SWIOTLB_POOL_NONE, @@ -478,6 +479,48 @@ static bool __init swiotlb_kmalloc_needs_bounce(void) (dma_get_cache_alignment() > 1); } +/** + * swiotlb_adjusted_size() - get the prospective adjusted SWIOTLB size + * + * Return the size that confidential-computing guest sizing would select for + * the default pool, without changing the configured SWIOTLB size. An + * explicit swiotlb= size is always preserved. An explicit area count is + * included in the size calculation. Automatic area sizing is initialized + * later from the running kernel's possible CPU map and any resulting size + * adjustment is therefore not reflected in the returned size. + */ +unsigned long __init swiotlb_adjusted_size(void) +{ + unsigned long nslabs, size = swiotlb_size_or_default(); + + if (swiotlb_default_size_changed() || + !cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) + return size; + /* + * For SEV and TDX and CCA, all DMA has to occur via + * shared/unencrypted pages. Kernel uses SWIOTLB to make this + * happen without changing device drivers. However, depending on + * the workload being run, the default 64MB of SWIOTLB may not be + * enough and SWIOTLB may run out of buffers for DMA, resulting in + * I/O errors and/or performance degradation especially with high + * I/O workloads. + * + * Adjust the default size of SWIOTLB using a percentage of guest + * memory for SWIOTLB buffers. Also, as the SWIOTLB bounce buffer + * memory is allocated from low memory, ensure that the adjusted + * size is within the limits of low available memory. + * + * The percentage of guest memory used here for SWIOTLB buffers is + * more of an approximation of the static adjustment which 64MB for + * <1G, and ~128M to 256M for 1G-to-4G, i.e., the 6% + */ + size = memblock_phys_mem_size() * 6 / 100; + size = clamp_val(size, IO_TLB_DEFAULT_SIZE, SZ_1G); + nslabs = swiotlb_aligned_nslabs(size); + + return nslabs << IO_TLB_SHIFT; +} + static void __init swiotlb_adjust_pool_size(enum swiotlb_pool_policy policy) { @@ -494,6 +537,7 @@ swiotlb_adjust_pool_size(enum swiotlb_pool_policy policy) break; } case SWIOTLB_POOL_CC_GUEST: + swiotlb_adjust_size(swiotlb_adjusted_size()); break; case SWIOTLB_POOL_NONE: WARN(true, "Cannot adjust SWIOTLB size without a pool\n"); @@ -509,7 +553,8 @@ swiotlb_select_pool_policy(unsigned int flags) if (swiotlb_force_disable) return SWIOTLB_POOL_NONE; - if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) + if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) && + !restricted_dma_pool_present) return SWIOTLB_POOL_CC_GUEST; if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) @@ -2155,6 +2200,8 @@ static int __init rmem_swiotlb_setup(unsigned long node, of_get_flat_dt_prop(node, "no-map", NULL)) return -EINVAL; + restricted_dma_pool_present = true; + pr_info("Reserved memory: created restricted DMA pool at %pa, size %ld MiB\n", &rmem->base, (unsigned long)rmem->size / SZ_1M); return 0; -- 2.43.0
