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. 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. Reviewed-by: Catalin Marinas <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: [email protected] Cc: "H. Peter Anvin" <[email protected]> Cc: Marek Szyprowski <[email protected]> Cc: Robin Murphy <[email protected]> Signed-off-by: Aneesh Kumar K.V (Arm) <[email protected]> --- arch/x86/mm/mem_encrypt.c | 24 ------------------------ kernel/dma/swiotlb.c | 27 +++++++++++++++++++++++++-- 2 files changed, 25 insertions(+), 26 deletions(-) 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/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 75ee63cd354e..e626cca63ad1 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -33,6 +33,7 @@ #include <linux/kmsan-checks.h> #include <linux/iommu-helper.h> #include <linux/init.h> +#include <linux/math64.h> #include <linux/memblock.h> #include <linux/mm.h> #include <linux/pfn.h> @@ -80,6 +81,7 @@ 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, @@ -478,7 +480,25 @@ swiotlb_adjust_pool_size(enum swiotlb_pool_policy policy) size = min(swiotlb_default_pool_size(), size); break; case SWIOTLB_POOL_CC_GUEST: - return; + /* + * 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. + * + * 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 = div_u64((u64)memblock_phys_mem_size() * 6, 100); + size = clamp_val(size, IO_TLB_DEFAULT_SIZE, SZ_1G); + break; case SWIOTLB_POOL_NONE: WARN(true, "Cannot adjust SWIOTLB size without a pool\n"); return; @@ -496,7 +516,8 @@ 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)) @@ -2142,6 +2163,8 @@ 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
