linux-kernel - Re: [PATCH v3 4/5] ring-buffer: Use flush_kernel_vmap_range() over flush_dcache

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Message-ID: <20250401163910.256c3177@gandalf.local.home>
Date: Tue, 1 Apr 2025 16:39:10 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, Mathieu
 Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Vincent Donnefort <vdonnefort@...gle.com>,
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Jann
 Horn <jannh@...gle.com>
Subject: Re: [PATCH v3 4/5] ring-buffer: Use flush_kernel_vmap_range() over
 flush_dcache_folio()

On Tue, 01 Apr 2025 16:25:53 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

>  
>  static void
> @@ -7319,7 +7319,8 @@ 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));
> +	flush_kernel_vmap_range(cpu_buffer->reader_page->page,
> +				buffer->subbuf_size + BUF_PAGE_HDR_SIZE);
>  
>  	rb_update_meta_page(cpu_buffer);
>  

This patch actually fixes a bug (I need to update the change log).

The previous code only flushed a page. But if the sub-buffer size was 2 or
more pages, it would not flush the rest of the sub-buffer.

-- Steve