[PATCH v6 6/8] dma: swiotlb: Centralize memory-encryption pool sizing

[Aneesh Kumar K.V (Arm)]

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 <catalin.marinas at arm.com>
Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at kernel.org>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Borislav Petkov <bp at alien8.de>
Cc: x86 at kernel.org
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: Marek Szyprowski <m.szyprowski at samsung.com>
Cc: Robin Murphy <robin.murphy at arm.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar at kernel.org>
---
 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