Re: [RFC PATCH v2 1/2] dma: swiotlb: Centralize default pool initialization and sizing

The addressing_limited argument to swiotlb_init() no longer describes
all the reasons why a default swiotlb pool may be needed. Confidential
computing systems need a shared pool even without addressing limitations,
while some systems need a smaller pool for bouncing unaligned kmalloc
buffers.

Replace the argument with SWIOTLB_INIT_ADDRESSING_LIMIT and
SWIOTLB_INIT_CC_SHARED reason flags, and add swiotlb_should_init() to
determine whether initialization is required for limited DMA addressing,
confidential-computing shared DMA, unaligned kmalloc bouncing, or
swiotlb=force.

Have architectures report addressing-limit and confidential-computing
requirements before swiotlb_init(). Mark CC pools shared before their
memory attributes are updated, and keep both addressing-limited and
CC-shared pools at their normal size instead of applying the reduced
kmalloc-only sizing policy.

Move the reduced kmalloc-bounce sizing policy from arm64 and RISC-V into
the SWIOTLB core. This keeps architecture code responsible for reporting
why a pool is needed while centralizing initialization and sizing
decisions.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 arch/arm/mm/init.c                   |  6 +++-
 arch/arm64/mm/init.c                 | 18 ++++------
 arch/loongarch/kernel/setup.c        |  2 +-
 arch/mips/cavium-octeon/dma-octeon.c |  2 +-
 arch/mips/loongson64/dma.c           |  2 +-
 arch/mips/sibyte/common/dma.c        |  2 +-
 arch/powerpc/kernel/dma-swiotlb.c    |  4 ++-
 arch/powerpc/mm/mem.c                | 15 +++++++-
 arch/powerpc/platforms/pseries/svm.c | 10 ------
 arch/powerpc/sysdev/fsl_pci.c        |  1 +
 arch/riscv/mm/init.c                 | 18 +++-------
 arch/s390/mm/init.c                  |  2 +-
 arch/x86/include/asm/iommu.h         |  2 ++
 arch/x86/kernel/amd_gart_64.c        |  1 +
 arch/x86/kernel/pci-dma.c            | 17 +++++----
 arch/x86/mm/mem_encrypt.c            |  4 +++
 include/linux/swiotlb.h              | 12 ++++---
 kernel/dma/swiotlb.c                 | 52 ++++++++++++++++++++++++----
 18 files changed, 109 insertions(+), 61 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 0cc1bf04686d..aca97a4e5dcd 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c

@@ -223,7 +223,11 @@ static inline void poison_init_mem(void *s, size_t count)
 void __init arch_mm_preinit(void)
 {
 #ifdef CONFIG_ARM_LPAE
-	swiotlb_init(max_pfn > arm_dma_pfn_limit, SWIOTLB_VERBOSE);
+	unsigned int flags = SWIOTLB_VERBOSE;
+
+	if (max_pfn > arm_dma_pfn_limit)
+		flags |= SWIOTLB_INIT_ADDRESSING_LIMIT;
+	swiotlb_init(flags);
 #endif
 
 #ifdef CONFIG_SA1111

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index e308a7cabd12..9f5b366d2086 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c

@@ -338,19 +338,15 @@ void __init arch_setup_zero_pages(void)
 void __init arch_mm_preinit(void)
 {
 	unsigned int flags = SWIOTLB_VERBOSE;
+	/* pKVM uses restricted-dma-pool */
+	bool cc_guest = is_realm_world();
 
-	if (max_pfn <= PFN_DOWN(arm64_dma_phys_limit)) {
-		/*
-		 * If no bouncing needed for ZONE_DMA, reduce the swiotlb
-		 * buffer for kmalloc() bouncing to 1MB per 1GB of RAM.
-		 */
-		unsigned long size =
-			DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
-
-		swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
-	}
+	if (cc_guest)
+		flags |= SWIOTLB_INIT_CC_SHARED;
+	else if (max_pfn > PFN_DOWN(arm64_dma_phys_limit))
+		flags |= SWIOTLB_INIT_ADDRESSING_LIMIT;
 
-	swiotlb_init(true, flags);
+	swiotlb_init(flags);