Re: [PATCH v9 00/10] arm64: Unmap FF-A lent memory from direct map

[Vincent Donnefort <vdonnefort@google.com>]

This is of course v1, not v9...

On Wed, Sep 02, 2026 at 11:47:02AM +0100, Vincent Donnefort wrote:
> This series is a follow-up to the discussion that has started here [1].
> While standalone, it also provides primitives reusable for the VPR DMA
> heap.
> 
> 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 the "arm,ffa-lend-pool" CMA
> driver to manage unmapping and remapping on lend/reclaim transitions:
> 
> 1. memblock & OF reserved memory ("ll-map"):
>    - Introduce MEMBLOCK_LLMAP and the DT "ll-map" property for reserved-memory
>      nodes to force last-level (PTE) mappings only for a specific region.
> 
> 2. set_memory infrastructure:
>    - Introduce can_set_direct_map_range() to check if a specific address
>      range is mapped with last-level entries and can be modified safely.
>    - Introduce __set_direct_map_*() variants that bypass redundant checks
>      when the caller has already validated the range.
> 
> 3. "arm,ffa-lend-pool" driver
>    - Introduce the "arm,ffa-lend-pool" CMA reserved-memory driver, which
>      unmaps pages prior to lending (ffa_prepare_lend()) and restores them
>      when reclaimed (ffa_lend_reclaimed()).
> 
> 4. Optee support
>    - Hook OP-TEE dynamic protected memory pools to "arm,ffa-lend-pool" for
>      both SMC (via DT memory-region phandle) and FF-A (via
>      ffa_lend_pool_attach()) transports.
> 
> 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
> 
> Vincent Donnefort (10):
>   memblock: Introduce MEMBLOCK_LLMAP
>   of: reserved_mem: Introduce "ll-map" property
>   set_memory.h: Introduce can_set_direct_map_range()
>   set_memory.h: Introduce __set_direct_map*()
>   arm64: can_set_direct_map() if BBML3
>   arm64: Implement can_set_direct_map_range()
>   arm64: Implement __set_direct_map*()
>   arm64: Add support for MEMBLOCK_LLMAP
>   firmware: arm_ffa: Introduce ffa-lend-pool
>   optee: Add support for arm,ffa-lend-pool
> 
>  arch/arm64/include/asm/set_memory.h  |   7 +
>  arch/arm64/mm/mmu.c                  |  23 ++-
>  arch/arm64/mm/pageattr.c             |  67 +++++++-
>  drivers/firmware/arm_ffa/Kconfig     |   5 +
>  drivers/firmware/arm_ffa/Makefile    |   1 +
>  drivers/firmware/arm_ffa/lend_pool.c | 223 +++++++++++++++++++++++++++
>  drivers/of/of_reserved_mem.c         | 104 ++++++++++---
>  drivers/tee/optee/ffa_abi.c          |  13 +-
>  drivers/tee/optee/protmem.c          |   8 -
>  drivers/tee/optee/smc_abi.c          |  17 +-
>  drivers/tee/tee_shm.c                |  11 +-
>  include/linux/arm_ffa.h              |  21 +++
>  include/linux/memblock.h             |   9 ++
>  include/linux/set_memory.h           |  39 +++++
>  mm/memblock.c                        |  50 ++++++
>  15 files changed, 545 insertions(+), 53 deletions(-)
>  create mode 100644 drivers/firmware/arm_ffa/lend_pool.c
> 
> 
> base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
> -- 
> 2.55.0.970.g62bdec98f9-goog
> 

-- 
Vincent