This series is a follow-up to the discussion that has started here [1].
When memory is lent to the Secure world via FF-A, CPU speculative accesses from NS to the lent pages can still occur as long as it retains a cacheable mapping to it.
Ideally, lent memory would be "no-map" but that would mean giving up MiBs of useful memory, so let's try to do better with the help of a CMA pool.
On arm64, modifying the direct map at runtime is generally restricted because the linear map defaults to block mapping and splitting blocks at runtime may trigger fatal page fault, unless the CPU implements BBML3 or the entire direct map was mapped at page granularity from boot. Forcing last-level mappings system-wide incurs a severe penalty we want to avoid. Instead, this series introduces targeted last-level mappings for designated memory regions, along with a generic "lendable-dma-pool" CMA driver to manage unmapping and remapping on lend/reclaim transitions:
1. memblock: - Introduce MEMBLOCK_PTEMAP to force PTE mappings only for a specific region.
2. dma-mapping: - Introduce the "lendable-dma-pool" CMA reserved-memory driver, along with generic dma_zap_direct_map() and dma_restore_direct_map() APIs to unmap pages from the direct map and restore them.
3. arm64 direct map support: - Implement the "lendable-dma-pool" hooks.
4. OP-TEE support: - Hook OP-TEE dynamic protected memory allocation (tee_shm_alloc_dma_mem()) to dma_zap_direct_map() and dma_restore_direct_map().
Testing: ========
Tested with QEMU v8 using OP-TEE OS (built with CFG_CORE_DYN_PROTMEM=y) under both SMC and FF-A transports [2]
static void dump_direct_map(const char *label) { printf("\n=== %s ===\n", label); fflush(stdout); system("sed -n '/Linear Mapping start/,/Linear Mapping end/p' /sys/kernel/debug/kernel_page_tables"); fflush(stdout); }
int main(int argc, char *argv[]) { int heap_fd; int dmabuf_fd; struct dma_heap_allocation_data data = { 0 }; size_t size = 1024 * 1024; /* 1MB */
if (argc > 1) size = strtoul(argv[1], NULL, 0);
dump_direct_map("BEFORE ALLOCATION");
heap_fd = open("/dev/dma_heap/protected,secure-video", O_RDWR); if (heap_fd < 0) { perror("open /dev/dma_heap/protected,secure-video"); return 1; }
printf("\nOpened /dev/dma_heap/protected,secure-video\n"); printf("Allocating %zu bytes of protected memory via DMA heap...\n", size);
data.len = size; data.fd_flags = O_RDWR | O_CLOEXEC; if (ioctl(heap_fd, DMA_HEAP_IOCTL_ALLOC, &data) < 0) { perror("ioctl DMA_HEAP_IOCTL_ALLOC"); close(heap_fd); return 1; }
dmabuf_fd = data.fd; printf("Successfully allocated %zu bytes! dmabuf_fd = %d\n", size, dmabuf_fd);
dump_direct_map("DURING LEND (EXPECT HOLE IN DIRECT MAP)");
printf("\nReleasing dmabuf_fd...\n"); close(dmabuf_fd); close(heap_fd);
dump_direct_map("AFTER RECLAIM (RESTORED DIRECT MAP)");
return 0; }
[1] https://lore.kernel.org/all/20260807-tegra-vpr-v4-7-5510d16af89e@nvidia.com/ [2] https://optee.readthedocs.io/en/latest/building/gits/build.html#qemu-v8
Changelog:
v3: - Replace "arm,ffa-lend-pool" and OP-TEE "memory-region" DT binding with generic "lendable-dma-pool" compatible with "linux,cma-default" (Sumit). - move conflict check to flag-setting time in memblock_setclr_flag() (Mike) - Rebase onto v7.4-rc1.
v2 (https://lore.kernel.org/all/20260921110050.3977591-1-vdonnefort@google.com/): - Rename MEMBLOCK_LLMAP to MEMBLOCK_PTEMAP (Mike) - Warn on conflicting MEMBLOCK_NOMAP and MEMBLOCK_PTEMAP flags (Mike) - Drop DT "ll-map" property and mark MEMBLOCK_PTEMAP from ffa_lend_pool_setup() (Rob, Thierry) - Drop "reusable" and "no-map" property checks from ffa_lend_pool_setup() (Rob) - dt-bindings: Document arm,ffa-lend-pool (Rob) - Rework the Optee support with a separate ffa_lend_pool.c file. - use walk_kernel_page_table_range_lockless() for can_set_direct_map_range() to fix folded page table (Sashiko) - Add missing TLB flush in ffa_prepare_lend() - Disable hibernation - Rebase on linux-next (next-20260918) to use the new set_direct_map*() ranges (Mike)
v1 (https://lore.kernel.org/all/20260902104712.2399797-1-vdonnefort@google.com/)
Vincent Donnefort (8): memblock: Introduce MEMBLOCK_PTEMAP arm64: Add support for MEMBLOCK_PTEMAP dma-contiguous: Expose rmem_cma_ops dt-bindings: reserved-memory: Add lendable-dma-pool dma-mapping: Introduce lendable-dma-pool arm64: Introduce direct_map_is_ptemap() arm64: Add support for lendable-dma-pool optee: Add support for lendable-dma-pool
.../reserved-memory/lendable-dma-pool.yaml | 58 +++++ arch/arm64/Kconfig | 1 + arch/arm64/include/asm/set_memory.h | 6 + arch/arm64/mm/dma-mapping.c | 71 +++++ arch/arm64/mm/mmu.c | 22 +- arch/arm64/mm/pageattr.c | 121 ++++++++- drivers/tee/optee/protmem.c | 48 +++- include/linux/dma-map-ops.h | 9 + include/linux/dma-mapping.h | 16 ++ include/linux/memblock.h | 9 + kernel/dma/Kconfig | 3 + kernel/dma/Makefile | 1 + kernel/dma/contiguous.c | 4 +- kernel/dma/contiguous.h | 10 + kernel/dma/lendable.c | 243 ++++++++++++++++++ mm/memblock.c | 39 ++- 16 files changed, 630 insertions(+), 31 deletions(-) create mode 100644 Documentation/devicetree/bindings/reserved-memory/lendable-dma-pool.yaml create mode 100644 kernel/dma/contiguous.h create mode 100644 kernel/dma/lendable.c
base-commit: 6628e7d4c6b25c8d18f1345e3a20d21829aae7e4