From 34ea8fa084dd96a2e130ec871ade9ed3003f7eea Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 2 Apr 2025 10:49:05 -0400 Subject: [PATCH] tracing: Have reserve_mem use phys_to_virt() and separate from memmap buffer The reserve_mem kernel command line option may pass back a physical address, but the memory is still part of the normal memory just like using memblock_alloc() would be. This means that the physical memory returned by the reserve_mem command line option can be converted directly to virtual memory by simply using phys_to_virt(). When freeing the buffer there's no need to call vunmap() anymore as the memory allocated by reserve_mem is freed by the call to reserve_mem_release_by_name(). Because the persistent ring buffer can also be allocated via the memmap option, which *is* different than normal memory as it cannot be added back to the buddy system, it must be treated differently. It still needs to be virtually mapped to have access to it. It also can not be freed nor can it ever be memory mapped to user space. Create a new trace_array flag called TRACE_ARRAY_FL_MEMMAP which gets set if the buffer is created by the memmap option, and this will prevent the buffer from being memory mapped by user space. Also increment the ref count for memmap'ed buffers so that they can never be freed. Link: https://lore.kernel.org/all/Z-wFszhJ_9o4dc8O@kernel.org/ Cc: Linus Torvalds Cc: Masami Hiramatsu Cc: Mark Rutland Cc: Mathieu Desnoyers Cc: Andrew Morton Cc: Vincent Donnefort Cc: Vlastimil Babka Cc: Jann Horn Link: https://lore.kernel.org/20250402144953.583750106@goodmis.org Suggested-by: Mike Rapoport Signed-off-by: Steven Rostedt (Google) --- kernel/trace/trace.c | 23 ++++++++++++++++------- kernel/trace/trace.h | 1 + 2 files changed, 17 insertions(+), 7 deletions(-) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 96129985e81c..e58b72e61573 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8492,6 +8492,10 @@ static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma) struct trace_iterator *iter = &info->iter; int ret = 0; + /* A memmap'ed buffer is not supported for user space mmap */ + if (iter->tr->flags & TRACE_ARRAY_FL_MEMMAP) + return -ENODEV; + /* Currently the boot mapped buffer is not supported for mmap */ if (iter->tr->flags & TRACE_ARRAY_FL_BOOT) return -ENODEV; @@ -9600,9 +9604,6 @@ static void free_trace_buffers(struct trace_array *tr) #ifdef CONFIG_TRACER_MAX_TRACE free_trace_buffer(&tr->max_buffer); #endif - - if (tr->range_addr_start) - vunmap((void *)tr->range_addr_start); } static void init_trace_flags_index(struct trace_array *tr) @@ -10696,6 +10697,7 @@ static inline void do_allocate_snapshot(const char *name) { } __init static void enable_instances(void) { struct trace_array *tr; + bool memmap_area = false; char *curr_str; char *name; char *str; @@ -10764,6 +10766,7 @@ __init static void enable_instances(void) name); continue; } + memmap_area = true; } else if (tok) { if (!reserve_mem_find_by_name(tok, &start, &size)) { start = 0; @@ -10784,7 +10787,10 @@ __init static void enable_instances(void) continue; } - addr = map_pages(start, size); + if (memmap_area) + addr = map_pages(start, size); + else + addr = (unsigned long)phys_to_virt(start); if (addr) { pr_info("Tracing: mapped boot instance %s at physical memory %pa of size 0x%lx\n", name, &start, (unsigned long)size); @@ -10811,10 +10817,13 @@ __init static void enable_instances(void) update_printk_trace(tr); /* - * If start is set, then this is a mapped buffer, and - * cannot be deleted by user space, so keep the reference - * to it. + * memmap'd buffers can not be freed. */ + if (memmap_area) { + tr->flags |= TRACE_ARRAY_FL_MEMMAP; + tr->ref++; + } + if (start) { tr->flags |= TRACE_ARRAY_FL_BOOT | TRACE_ARRAY_FL_LAST_BOOT; tr->range_name = no_free_ptr(rname); diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index ab7c7a1930cc..9d9dcfad6269 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -446,6 +446,7 @@ enum { TRACE_ARRAY_FL_BOOT = BIT(1), TRACE_ARRAY_FL_LAST_BOOT = BIT(2), TRACE_ARRAY_FL_MOD_INIT = BIT(3), + TRACE_ARRAY_FL_MEMMAP = BIT(4), }; #ifdef CONFIG_MODULES