On Fri, May 14, 2021 at 10:50:55AM +0200, David Hildenbrand wrote:

On 13.05.21 20:47, Mike Rapoport wrote:

quoted

From: Mike Rapoport <redacted>

Removing of the pages from the direct map may cause its fragmentation
on architectures that use large pages to map the physical memory
which affects the system performance. However, the original Kconfig
text for CONFIG_DIRECT_GBPAGES said that gigabyte pages in the direct
map "... can improve the kernel's performance a tiny bit ..." (commit
00d1c5e05736 ("x86: add gbpages switches")) and the recent report [1]
showed that "... although 1G mappings are a good default choice,
there is no compelling evidence that it must be the only choice".
Hence, it is sufficient to have secretmem disabled by default with
the ability of a system administrator to enable it at boot time.

Maybe add a link to the Intel performance evaluation.

 
" ... the recent report [1]" and the link below.
 

quoted

Pages in the secretmem regions are unevictable and unmovable to
avoid accidental exposure of the sensitive data via swap or during
page migration.

 
...

quoted

A page that was a part of the secret memory area is cleared when it
is freed to ensure the data is not exposed to the next user of that
page.

You could skip that with init_on_free (and eventually also with
init_on_alloc) set to avoid double clearing.

Right, but for now I'd prefer to keep this explicit in the secretmem
implementation. We may add the check for init_on_free/init_on_alloc later
on.

quoted

[1]
https://lore.kernel.org/linux-mm/213b4567-46ce-f116-9cdf-bbd0c884eb3c@linux.intel.com/ (local)

-- 
Sincerely yours,
Mike.