On Fri, 14 Feb 2025 13:04:42 -0500 Steven Rostedt <[email protected]> wrote:
> From: Steven Rostedt <[email protected]> > > The persistent ring buffer uses vmap()'d memory to map the reserved memory > from boot. But the user space mmap() to the ring buffer requires > virt_to_page() to return a valid page. But that only works for core kernel > addresses and not for vmap() addresses. > > If virt_addr_valid() fails on the page to be mapped, use vmalloc_to_page() > instead. > > Also, the persistent memory uses the page->id for its own purpose where as > the user mmap buffer currently uses that for the subbuf array mapped to > user space. If the buffer is a persistent buffer, use the page index into > that buffer as the identifier instead of the page->id. > > That is, the page->id for a persistent buffer, represents the order of the > buffer is in the link list. ->id == 0 means it is the reader page. > When a reader page is swapped, the new reader page's ->id gets zero, and > the old reader page gets the ->id of the page that it swapped with. > > The user space mapping has the ->id is the index of where it was mapped in > user space and does not change while it is mapped. > > Since the persistent buffer is fixed in its location, the index of where > a page is in the memory range can be used as the "id" to put in the meta > page array, and it can be mapped in the same order to user space as it is > in the persistent memory. Looks good and works for me. Reviewed-by: Masami Hiramatsu (Google) <[email protected]> Tested-by: Masami Hiramatsu (Google) <[email protected]> Thank you, > > Signed-off-by: Steven Rostedt (Google) <[email protected]> > --- > kernel/trace/ring_buffer.c | 49 ++++++++++++++++++++++++++++++++------ > kernel/trace/trace.c | 4 ---- > 2 files changed, 42 insertions(+), 11 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index bb6089c2951e..87caf9d48edb 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -5950,12 +5950,18 @@ static void rb_clear_buffer_page(struct buffer_page > *page) > static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) > { > struct trace_buffer_meta *meta = cpu_buffer->meta_page; > + struct page *page; > > if (!meta) > return; > > meta->reader.read = cpu_buffer->reader_page->read; > - meta->reader.id = cpu_buffer->reader_page->id; > + /* For boot buffers, the id is the index */ > + if (cpu_buffer->ring_meta) > + meta->reader.id = rb_meta_subbuf_idx(cpu_buffer->ring_meta, > + > cpu_buffer->reader_page->page); > + else > + meta->reader.id = cpu_buffer->reader_page->id; > meta->reader.lost_events = cpu_buffer->lost_events; > > meta->entries = local_read(&cpu_buffer->entries); > @@ -5963,7 +5969,12 @@ static void rb_update_meta_page(struct > ring_buffer_per_cpu *cpu_buffer) > meta->read = cpu_buffer->read; > > /* Some archs do not have data cache coherency between kernel and > user-space */ > - flush_dcache_folio(virt_to_folio(cpu_buffer->meta_page)); > + if (virt_addr_valid(cpu_buffer->meta_page)) > + page = virt_to_page(cpu_buffer->meta_page); > + else > + page = vmalloc_to_page(cpu_buffer->meta_page); > + > + flush_dcache_folio(page_folio(page)); > } > > static void > @@ -6883,23 +6894,38 @@ static void rb_setup_ids_meta_page(struct > ring_buffer_per_cpu *cpu_buffer, > struct trace_buffer_meta *meta = cpu_buffer->meta_page; > unsigned int nr_subbufs = cpu_buffer->nr_pages + 1; > struct buffer_page *first_subbuf, *subbuf; > + int cnt = 0; > int id = 0; > > - subbuf_ids[id] = (unsigned long)cpu_buffer->reader_page->page; > - cpu_buffer->reader_page->id = id++; > + if (cpu_buffer->ring_meta) > + id = rb_meta_subbuf_idx(cpu_buffer->ring_meta, > + cpu_buffer->reader_page->page); > + else > + cpu_buffer->reader_page->id = id; > + > + subbuf_ids[id++] = (unsigned long)cpu_buffer->reader_page->page; > + cnt++; > > first_subbuf = subbuf = rb_set_head_page(cpu_buffer); > do { > + if (cpu_buffer->ring_meta) > + id = rb_meta_subbuf_idx(cpu_buffer->ring_meta, > + subbuf->page); > + else > + subbuf->id = id; > + > if (WARN_ON(id >= nr_subbufs)) > break; > > subbuf_ids[id] = (unsigned long)subbuf->page; > - subbuf->id = id; > > rb_inc_page(&subbuf); > id++; > + cnt++; > } while (subbuf != first_subbuf); > > + WARN_ON(cnt != nr_subbufs); > + > /* install subbuf ID to kern VA translation */ > cpu_buffer->subbuf_ids = subbuf_ids; > > @@ -7064,7 +7090,10 @@ static int __rb_map_vma(struct ring_buffer_per_cpu > *cpu_buffer, > goto out; > } > > - page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]); > + if (virt_addr_valid(cpu_buffer->subbuf_ids[s])) > + page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]); > + else > + page = vmalloc_to_page((void > *)cpu_buffer->subbuf_ids[s]); > > for (; off < (1 << (subbuf_order)); off++, page++) { > if (p >= nr_pages) > @@ -7210,6 +7239,7 @@ int ring_buffer_map_get_reader(struct trace_buffer > *buffer, int cpu) > unsigned long missed_events; > unsigned long reader_size; > unsigned long flags; > + struct page *page; > > cpu_buffer = rb_get_mapped_buffer(buffer, cpu); > if (IS_ERR(cpu_buffer)) > @@ -7278,7 +7308,12 @@ int ring_buffer_map_get_reader(struct trace_buffer > *buffer, int cpu) > > out: > /* Some archs do not have data cache coherency between kernel and > user-space */ > - flush_dcache_folio(virt_to_folio(cpu_buffer->reader_page->page)); > + if (virt_addr_valid(cpu_buffer->meta_page)) > + page = virt_to_page(cpu_buffer->meta_page); > + else > + page = vmalloc_to_page(cpu_buffer->meta_page); > + > + flush_dcache_folio(page_folio(page)); > > rb_update_meta_page(cpu_buffer); > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 0e6d517e74e0..25ff37aab00f 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -8279,10 +8279,6 @@ static int tracing_buffers_mmap(struct file *filp, > struct vm_area_struct *vma) > struct trace_iterator *iter = &info->iter; > int ret = 0; > > - /* Currently the boot mapped buffer is not supported for mmap */ > - if (iter->tr->flags & TRACE_ARRAY_FL_BOOT) > - return -ENODEV; > - > ret = get_snapshot_map(iter->tr); > if (ret) > return ret; > -- > 2.47.2 > -- Masami Hiramatsu (Google) <[email protected]>
