Re: [PATCH 05/15] Add io_uring IO interface

On 1/17/19 5:02 AM, Roman Penyaev wrote:

Hi Jens,

On 2019-01-16 18:49, Jens Axboe wrote:

[...]

quoted

+static void *io_mem_alloc(size_t size)
+{
+	gfp_t gfp_flags = GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_COMP 
|
+				__GFP_NORETRY;
+
+	return (void *) __get_free_pages(gfp_flags, get_order(size));

Since these pages are shared between kernel and userspace, do we need
to care about d-cache aliasing on armv6 (or other "strange" archs
which I've never seen) with vivt or vipt cpu caches?

E.g. vmalloc_user() targets this problem by aligning kernel address
on SHMLBA, so no flush_dcache_page() is required.

I'm honestly not sure, it'd be trivial enough to stick a
flush_dcache_page() into the few areas we'd need it. The rings are
already page (SHMLBA) aligned.

-- 
Jens Axboe